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32 results

hugetlb.c

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  • hugetlb.c 156.02 KiB
    // SPDX-License-Identifier: GPL-2.0-only
    /*
     * Generic hugetlb support.
     * (C) Nadia Yvette Chambers, April 2004
     */
    #include <linux/list.h>
    #include <linux/init.h>
    #include <linux/mm.h>
    #include <linux/seq_file.h>
    #include <linux/sysctl.h>
    #include <linux/highmem.h>
    #include <linux/mmu_notifier.h>
    #include <linux/nodemask.h>
    #include <linux/pagemap.h>
    #include <linux/mempolicy.h>
    #include <linux/compiler.h>
    #include <linux/cpuset.h>
    #include <linux/mutex.h>
    #include <linux/memblock.h>
    #include <linux/sysfs.h>
    #include <linux/slab.h>
    #include <linux/sched/mm.h>
    #include <linux/mmdebug.h>
    #include <linux/sched/signal.h>
    #include <linux/rmap.h>
    #include <linux/string_helpers.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    #include <linux/jhash.h>
    #include <linux/numa.h>
    #include <linux/llist.h>
    #include <linux/cma.h>
    
    #include <asm/page.h>
    #include <asm/pgalloc.h>
    #include <asm/tlb.h>
    
    #include <linux/io.h>
    #include <linux/hugetlb.h>
    #include <linux/hugetlb_cgroup.h>
    #include <linux/node.h>
    #include <linux/userfaultfd_k.h>
    #include <linux/page_owner.h>
    #include "internal.h"
    
    int hugetlb_max_hstate __read_mostly;
    unsigned int default_hstate_idx;
    struct hstate hstates[HUGE_MAX_HSTATE];
    
    #ifdef CONFIG_CMA
    static struct cma *hugetlb_cma[MAX_NUMNODES];
    #endif
    static unsigned long hugetlb_cma_size __initdata;
    
    /*
     * Minimum page order among possible hugepage sizes, set to a proper value
     * at boot time.
     */
    static unsigned int minimum_order __read_mostly = UINT_MAX;
    
    __initdata LIST_HEAD(huge_boot_pages);
    
    /* for command line parsing */
    static struct hstate * __initdata parsed_hstate;
    static unsigned long __initdata default_hstate_max_huge_pages;
    static bool __initdata parsed_valid_hugepagesz = true;
    static bool __initdata parsed_default_hugepagesz;
    
    /*
     * Protects updates to hugepage_freelists, hugepage_activelist, nr_huge_pages,
     * free_huge_pages, and surplus_huge_pages.
     */
    DEFINE_SPINLOCK(hugetlb_lock);
    
    /*
     * Serializes faults on the same logical page.  This is used to
     * prevent spurious OOMs when the hugepage pool is fully utilized.
     */
    static int num_fault_mutexes;
    struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp;
    
    static inline bool PageHugeFreed(struct page *head)
    {
    	return page_private(head + 4) == -1UL;
    }
    
    static inline void SetPageHugeFreed(struct page *head)
    {
    	set_page_private(head + 4, -1UL);
    }
    
    static inline void ClearPageHugeFreed(struct page *head)
    {
    	set_page_private(head + 4, 0);
    }
    
    /* Forward declaration */
    static int hugetlb_acct_memory(struct hstate *h, long delta);
    
    static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
    {
    	bool free = (spool->count == 0) && (spool->used_hpages == 0);
    
    	spin_unlock(&spool->lock);
    
    	/* If no pages are used, and no other handles to the subpool
    	 * remain, give up any reservations based on minimum size and
    	 * free the subpool */
    	if (free) {
    		if (spool->min_hpages != -1)
    			hugetlb_acct_memory(spool->hstate,
    						-spool->min_hpages);
    		kfree(spool);
    	}
    }
    
    struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
    						long min_hpages)
    {
    	struct hugepage_subpool *spool;
    
    	spool = kzalloc(sizeof(*spool), GFP_KERNEL);
    	if (!spool)
    		return NULL;
    
    	spin_lock_init(&spool->lock);
    	spool->count = 1;
    	spool->max_hpages = max_hpages;
    	spool->hstate = h;
    	spool->min_hpages = min_hpages;
    
    	if (min_hpages != -1 && hugetlb_acct_memory(h, min_hpages)) {
    		kfree(spool);
    		return NULL;
    	}
    	spool->rsv_hpages = min_hpages;
    
    	return spool;
    }
    
    void hugepage_put_subpool(struct hugepage_subpool *spool)
    {
    	spin_lock(&spool->lock);
    	BUG_ON(!spool->count);
    	spool->count--;
    	unlock_or_release_subpool(spool);
    }
    
    /*
     * Subpool accounting for allocating and reserving pages.
     * Return -ENOMEM if there are not enough resources to satisfy the
     * request.  Otherwise, return the number of pages by which the
     * global pools must be adjusted (upward).  The returned value may
     * only be different than the passed value (delta) in the case where
     * a subpool minimum size must be maintained.
     */
    static long hugepage_subpool_get_pages(struct hugepage_subpool *spool,
    				      long delta)
    {
    	long ret = delta;
    
    	if (!spool)
    		return ret;
    
    	spin_lock(&spool->lock);
    
    	if (spool->max_hpages != -1) {		/* maximum size accounting */
    		if ((spool->used_hpages + delta) <= spool->max_hpages)
    			spool->used_hpages += delta;
    		else {
    			ret = -ENOMEM;
    			goto unlock_ret;
    		}
    	}
    
    	/* minimum size accounting */
    	if (spool->min_hpages != -1 && spool->rsv_hpages) {
    		if (delta > spool->rsv_hpages) {
    			/*
    			 * Asking for more reserves than those already taken on
    			 * behalf of subpool.  Return difference.
    			 */
    			ret = delta - spool->rsv_hpages;
    			spool->rsv_hpages = 0;
    		} else {
    			ret = 0;	/* reserves already accounted for */
    			spool->rsv_hpages -= delta;
    		}
    	}
    
    unlock_ret:
    	spin_unlock(&spool->lock);
    	return ret;
    }
    
    /*
     * Subpool accounting for freeing and unreserving pages.
     * Return the number of global page reservations that must be dropped.
     * The return value may only be different than the passed value (delta)
     * in the case where a subpool minimum size must be maintained.
     */
    static long hugepage_subpool_put_pages(struct hugepage_subpool *spool,
    				       long delta)
    {
    	long ret = delta;
    
    	if (!spool)
    		return delta;
    
    	spin_lock(&spool->lock);
    
    	if (spool->max_hpages != -1)		/* maximum size accounting */
    		spool->used_hpages -= delta;
    
    	 /* minimum size accounting */
    	if (spool->min_hpages != -1 && spool->used_hpages < spool->min_hpages) {
    		if (spool->rsv_hpages + delta <= spool->min_hpages)
    			ret = 0;
    		else
    			ret = spool->rsv_hpages + delta - spool->min_hpages;
    
    		spool->rsv_hpages += delta;
    		if (spool->rsv_hpages > spool->min_hpages)
    			spool->rsv_hpages = spool->min_hpages;
    	}
    
    	/*
    	 * If hugetlbfs_put_super couldn't free spool due to an outstanding
    	 * quota reference, free it now.
    	 */
    	unlock_or_release_subpool(spool);
    
    	return ret;
    }
    
    static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
    {
    	return HUGETLBFS_SB(inode->i_sb)->spool;
    }
    
    static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
    {
    	return subpool_inode(file_inode(vma->vm_file));
    }
    
    /* Helper that removes a struct file_region from the resv_map cache and returns
     * it for use.
     */
    static struct file_region *
    get_file_region_entry_from_cache(struct resv_map *resv, long from, long to)
    {
    	struct file_region *nrg = NULL;
    
    	VM_BUG_ON(resv->region_cache_count <= 0);
    
    	resv->region_cache_count--;
    	nrg = list_first_entry(&resv->region_cache, struct file_region, link);
    	list_del(&nrg->link);
    
    	nrg->from = from;
    	nrg->to = to;
    
    	return nrg;
    }
    
    static void copy_hugetlb_cgroup_uncharge_info(struct file_region *nrg,
    					      struct file_region *rg)
    {
    #ifdef CONFIG_CGROUP_HUGETLB
    	nrg->reservation_counter = rg->reservation_counter;
    	nrg->css = rg->css;
    	if (rg->css)
    		css_get(rg->css);
    #endif
    }
    
    /* Helper that records hugetlb_cgroup uncharge info. */
    static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
    						struct hstate *h,
    						struct resv_map *resv,
    						struct file_region *nrg)
    {
    #ifdef CONFIG_CGROUP_HUGETLB
    	if (h_cg) {
    		nrg->reservation_counter =
    			&h_cg->rsvd_hugepage[hstate_index(h)];
    		nrg->css = &h_cg->css;
    		if (!resv->pages_per_hpage)
    			resv->pages_per_hpage = pages_per_huge_page(h);
    		/* pages_per_hpage should be the same for all entries in
    		 * a resv_map.
    		 */
    		VM_BUG_ON(resv->pages_per_hpage != pages_per_huge_page(h));
    	} else {
    		nrg->reservation_counter = NULL;
    		nrg->css = NULL;
    	}
    #endif
    }
    
    static bool has_same_uncharge_info(struct file_region *rg,
    				   struct file_region *org)
    {
    #ifdef CONFIG_CGROUP_HUGETLB
    	return rg && org &&
    	       rg->reservation_counter == org->reservation_counter &&
    	       rg->css == org->css;
    
    #else
    	return true;
    #endif
    }
    
    static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
    {
    	struct file_region *nrg = NULL, *prg = NULL;
    
    	prg = list_prev_entry(rg, link);
    	if (&prg->link != &resv->regions && prg->to == rg->from &&
    	    has_same_uncharge_info(prg, rg)) {
    		prg->to = rg->to;
    
    		list_del(&rg->link);
    		kfree(rg);
    
    		rg = prg;
    	}
    
    	nrg = list_next_entry(rg, link);
    	if (&nrg->link != &resv->regions && nrg->from == rg->to &&
    	    has_same_uncharge_info(nrg, rg)) {
    		nrg->from = rg->from;
    
    		list_del(&rg->link);
    		kfree(rg);
    	}
    }
    
    /*
     * Must be called with resv->lock held.
     *
     * Calling this with regions_needed != NULL will count the number of pages
     * to be added but will not modify the linked list. And regions_needed will
     * indicate the number of file_regions needed in the cache to carry out to add
     * the regions for this range.
     */
    static long add_reservation_in_range(struct resv_map *resv, long f, long t,
    				     struct hugetlb_cgroup *h_cg,
    				     struct hstate *h, long *regions_needed)
    {
    	long add = 0;
    	struct list_head *head = &resv->regions;
    	long last_accounted_offset = f;
    	struct file_region *rg = NULL, *trg = NULL, *nrg = NULL;
    
    	if (regions_needed)
    		*regions_needed = 0;
    
    	/* In this loop, we essentially handle an entry for the range
    	 * [last_accounted_offset, rg->from), at every iteration, with some
    	 * bounds checking.
    	 */
    	list_for_each_entry_safe(rg, trg, head, link) {
    		/* Skip irrelevant regions that start before our range. */
    		if (rg->from < f) {
    			/* If this region ends after the last accounted offset,
    			 * then we need to update last_accounted_offset.
    			 */
    			if (rg->to > last_accounted_offset)
    				last_accounted_offset = rg->to;
    			continue;
    		}
    
    		/* When we find a region that starts beyond our range, we've
    		 * finished.
    		 */
    		if (rg->from > t)
    			break;
    
    		/* Add an entry for last_accounted_offset -> rg->from, and
    		 * update last_accounted_offset.
    		 */
    		if (rg->from > last_accounted_offset) {
    			add += rg->from - last_accounted_offset;
    			if (!regions_needed) {
    				nrg = get_file_region_entry_from_cache(
    					resv, last_accounted_offset, rg->from);
    				record_hugetlb_cgroup_uncharge_info(h_cg, h,
    								    resv, nrg);
    				list_add(&nrg->link, rg->link.prev);
    				coalesce_file_region(resv, nrg);
    			} else
    				*regions_needed += 1;
    		}
    
    		last_accounted_offset = rg->to;
    	}
    
    	/* Handle the case where our range extends beyond
    	 * last_accounted_offset.
    	 */
    	if (last_accounted_offset < t) {
    		add += t - last_accounted_offset;
    		if (!regions_needed) {
    			nrg = get_file_region_entry_from_cache(
    				resv, last_accounted_offset, t);
    			record_hugetlb_cgroup_uncharge_info(h_cg, h, resv, nrg);
    			list_add(&nrg->link, rg->link.prev);
    			coalesce_file_region(resv, nrg);
    		} else
    			*regions_needed += 1;
    	}
    
    	VM_BUG_ON(add < 0);
    	return add;
    }
    
    /* Must be called with resv->lock acquired. Will drop lock to allocate entries.
     */
    static int allocate_file_region_entries(struct resv_map *resv,
    					int regions_needed)
    	__must_hold(&resv->lock)
    {
    	struct list_head allocated_regions;
    	int to_allocate = 0, i = 0;
    	struct file_region *trg = NULL, *rg = NULL;
    
    	VM_BUG_ON(regions_needed < 0);
    
    	INIT_LIST_HEAD(&allocated_regions);
    
    	/*
    	 * Check for sufficient descriptors in the cache to accommodate
    	 * the number of in progress add operations plus regions_needed.
    	 *
    	 * This is a while loop because when we drop the lock, some other call
    	 * to region_add or region_del may have consumed some region_entries,
    	 * so we keep looping here until we finally have enough entries for
    	 * (adds_in_progress + regions_needed).
    	 */
    	while (resv->region_cache_count <
    	       (resv->adds_in_progress + regions_needed)) {
    		to_allocate = resv->adds_in_progress + regions_needed -
    			      resv->region_cache_count;
    
    		/* At this point, we should have enough entries in the cache
    		 * for all the existings adds_in_progress. We should only be
    		 * needing to allocate for regions_needed.
    		 */
    		VM_BUG_ON(resv->region_cache_count < resv->adds_in_progress);
    
    		spin_unlock(&resv->lock);
    		for (i = 0; i < to_allocate; i++) {
    			trg = kmalloc(sizeof(*trg), GFP_KERNEL);
    			if (!trg)
    				goto out_of_memory;
    			list_add(&trg->link, &allocated_regions);
    		}
    
    		spin_lock(&resv->lock);
    
    		list_splice(&allocated_regions, &resv->region_cache);
    		resv->region_cache_count += to_allocate;
    	}
    
    	return 0;
    
    out_of_memory:
    	list_for_each_entry_safe(rg, trg, &allocated_regions, link) {
    		list_del(&rg->link);
    		kfree(rg);
    	}
    	return -ENOMEM;
    }
    
    /*
     * Add the huge page range represented by [f, t) to the reserve
     * map.  Regions will be taken from the cache to fill in this range.
     * Sufficient regions should exist in the cache due to the previous
     * call to region_chg with the same range, but in some cases the cache will not
     * have sufficient entries due to races with other code doing region_add or
     * region_del.  The extra needed entries will be allocated.
     *
     * regions_needed is the out value provided by a previous call to region_chg.
     *
     * Return the number of new huge pages added to the map.  This number is greater
     * than or equal to zero.  If file_region entries needed to be allocated for
     * this operation and we were not able to allocate, it returns -ENOMEM.
     * region_add of regions of length 1 never allocate file_regions and cannot
     * fail; region_chg will always allocate at least 1 entry and a region_add for
     * 1 page will only require at most 1 entry.
     */
    static long region_add(struct resv_map *resv, long f, long t,
    		       long in_regions_needed, struct hstate *h,
    		       struct hugetlb_cgroup *h_cg)
    {
    	long add = 0, actual_regions_needed = 0;
    
    	spin_lock(&resv->lock);
    retry:
    
    	/* Count how many regions are actually needed to execute this add. */
    	add_reservation_in_range(resv, f, t, NULL, NULL,
    				 &actual_regions_needed);
    
    	/*
    	 * Check for sufficient descriptors in the cache to accommodate
    	 * this add operation. Note that actual_regions_needed may be greater
    	 * than in_regions_needed, as the resv_map may have been modified since
    	 * the region_chg call. In this case, we need to make sure that we
    	 * allocate extra entries, such that we have enough for all the
    	 * existing adds_in_progress, plus the excess needed for this
    	 * operation.
    	 */
    	if (actual_regions_needed > in_regions_needed &&
    	    resv->region_cache_count <
    		    resv->adds_in_progress +
    			    (actual_regions_needed - in_regions_needed)) {
    		/* region_add operation of range 1 should never need to
    		 * allocate file_region entries.
    		 */
    		VM_BUG_ON(t - f <= 1);
    
    		if (allocate_file_region_entries(
    			    resv, actual_regions_needed - in_regions_needed)) {
    			return -ENOMEM;
    		}
    
    		goto retry;
    	}
    
    	add = add_reservation_in_range(resv, f, t, h_cg, h, NULL);
    
    	resv->adds_in_progress -= in_regions_needed;
    
    	spin_unlock(&resv->lock);
    	VM_BUG_ON(add < 0);
    	return add;
    }
    
    /*
     * Examine the existing reserve map and determine how many
     * huge pages in the specified range [f, t) are NOT currently
     * represented.  This routine is called before a subsequent
     * call to region_add that will actually modify the reserve
     * map to add the specified range [f, t).  region_chg does
     * not change the number of huge pages represented by the
     * map.  A number of new file_region structures is added to the cache as a
     * placeholder, for the subsequent region_add call to use. At least 1
     * file_region structure is added.
     *
     * out_regions_needed is the number of regions added to the
     * resv->adds_in_progress.  This value needs to be provided to a follow up call
     * to region_add or region_abort for proper accounting.
     *
     * Returns the number of huge pages that need to be added to the existing
     * reservation map for the range [f, t).  This number is greater or equal to
     * zero.  -ENOMEM is returned if a new file_region structure or cache entry
     * is needed and can not be allocated.
     */
    static long region_chg(struct resv_map *resv, long f, long t,
    		       long *out_regions_needed)
    {
    	long chg = 0;
    
    	spin_lock(&resv->lock);
    
    	/* Count how many hugepages in this range are NOT represented. */
    	chg = add_reservation_in_range(resv, f, t, NULL, NULL,
    				       out_regions_needed);
    
    	if (*out_regions_needed == 0)
    		*out_regions_needed = 1;
    
    	if (allocate_file_region_entries(resv, *out_regions_needed))
    		return -ENOMEM;
    
    	resv->adds_in_progress += *out_regions_needed;
    
    	spin_unlock(&resv->lock);
    	return chg;
    }
    
    /*
     * Abort the in progress add operation.  The adds_in_progress field
     * of the resv_map keeps track of the operations in progress between
     * calls to region_chg and region_add.  Operations are sometimes
     * aborted after the call to region_chg.  In such cases, region_abort
     * is called to decrement the adds_in_progress counter. regions_needed
     * is the value returned by the region_chg call, it is used to decrement
     * the adds_in_progress counter.
     *
     * NOTE: The range arguments [f, t) are not needed or used in this
     * routine.  They are kept to make reading the calling code easier as
     * arguments will match the associated region_chg call.
     */
    static void region_abort(struct resv_map *resv, long f, long t,
    			 long regions_needed)
    {
    	spin_lock(&resv->lock);
    	VM_BUG_ON(!resv->region_cache_count);
    	resv->adds_in_progress -= regions_needed;
    	spin_unlock(&resv->lock);
    }
    
    /*
     * Delete the specified range [f, t) from the reserve map.  If the
     * t parameter is LONG_MAX, this indicates that ALL regions after f
     * should be deleted.  Locate the regions which intersect [f, t)
     * and either trim, delete or split the existing regions.
     *
     * Returns the number of huge pages deleted from the reserve map.
     * In the normal case, the return value is zero or more.  In the
     * case where a region must be split, a new region descriptor must
     * be allocated.  If the allocation fails, -ENOMEM will be returned.
     * NOTE: If the parameter t == LONG_MAX, then we will never split
     * a region and possibly return -ENOMEM.  Callers specifying
     * t == LONG_MAX do not need to check for -ENOMEM error.
     */
    static long region_del(struct resv_map *resv, long f, long t)
    {
    	struct list_head *head = &resv->regions;
    	struct file_region *rg, *trg;
    	struct file_region *nrg = NULL;
    	long del = 0;
    
    retry:
    	spin_lock(&resv->lock);
    	list_for_each_entry_safe(rg, trg, head, link) {
    		/*
    		 * Skip regions before the range to be deleted.  file_region
    		 * ranges are normally of the form [from, to).  However, there
    		 * may be a "placeholder" entry in the map which is of the form
    		 * (from, to) with from == to.  Check for placeholder entries
    		 * at the beginning of the range to be deleted.
    		 */
    		if (rg->to <= f && (rg->to != rg->from || rg->to != f))
    			continue;
    
    		if (rg->from >= t)
    			break;
    
    		if (f > rg->from && t < rg->to) { /* Must split region */
    			/*
    			 * Check for an entry in the cache before dropping
    			 * lock and attempting allocation.
    			 */
    			if (!nrg &&
    			    resv->region_cache_count > resv->adds_in_progress) {
    				nrg = list_first_entry(&resv->region_cache,
    							struct file_region,
    							link);
    				list_del(&nrg->link);
    				resv->region_cache_count--;
    			}
    
    			if (!nrg) {
    				spin_unlock(&resv->lock);
    				nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
    				if (!nrg)
    					return -ENOMEM;
    				goto retry;
    			}
    
    			del += t - f;
    			hugetlb_cgroup_uncharge_file_region(
    				resv, rg, t - f);
    
    			/* New entry for end of split region */
    			nrg->from = t;
    			nrg->to = rg->to;
    
    			copy_hugetlb_cgroup_uncharge_info(nrg, rg);
    
    			INIT_LIST_HEAD(&nrg->link);
    
    			/* Original entry is trimmed */
    			rg->to = f;
    
    			list_add(&nrg->link, &rg->link);
    			nrg = NULL;
    			break;
    		}
    
    		if (f <= rg->from && t >= rg->to) { /* Remove entire region */
    			del += rg->to - rg->from;
    			hugetlb_cgroup_uncharge_file_region(resv, rg,
    							    rg->to - rg->from);
    			list_del(&rg->link);
    			kfree(rg);
    			continue;
    		}
    
    		if (f <= rg->from) {	/* Trim beginning of region */
    			hugetlb_cgroup_uncharge_file_region(resv, rg,
    							    t - rg->from);
    
    			del += t - rg->from;
    			rg->from = t;
    		} else {		/* Trim end of region */
    			hugetlb_cgroup_uncharge_file_region(resv, rg,
    							    rg->to - f);
    
    			del += rg->to - f;
    			rg->to = f;
    		}
    	}
    
    	spin_unlock(&resv->lock);
    	kfree(nrg);
    	return del;
    }
    
    /*
     * A rare out of memory error was encountered which prevented removal of
     * the reserve map region for a page.  The huge page itself was free'ed
     * and removed from the page cache.  This routine will adjust the subpool
     * usage count, and the global reserve count if needed.  By incrementing
     * these counts, the reserve map entry which could not be deleted will
     * appear as a "reserved" entry instead of simply dangling with incorrect
     * counts.
     */
    void hugetlb_fix_reserve_counts(struct inode *inode)
    {
    	struct hugepage_subpool *spool = subpool_inode(inode);
    	long rsv_adjust;
    
    	rsv_adjust = hugepage_subpool_get_pages(spool, 1);
    	if (rsv_adjust) {
    		struct hstate *h = hstate_inode(inode);
    
    		hugetlb_acct_memory(h, 1);
    	}
    }
    
    /*
     * Count and return the number of huge pages in the reserve map
     * that intersect with the range [f, t).
     */
    static long region_count(struct resv_map *resv, long f, long t)
    {
    	struct list_head *head = &resv->regions;
    	struct file_region *rg;
    	long chg = 0;
    
    	spin_lock(&resv->lock);
    	/* Locate each segment we overlap with, and count that overlap. */
    	list_for_each_entry(rg, head, link) {
    		long seg_from;
    		long seg_to;
    
    		if (rg->to <= f)
    			continue;
    		if (rg->from >= t)
    			break;
    
    		seg_from = max(rg->from, f);
    		seg_to = min(rg->to, t);
    
    		chg += seg_to - seg_from;
    	}
    	spin_unlock(&resv->lock);
    
    	return chg;
    }
    
    /*
     * Convert the address within this vma to the page offset within
     * the mapping, in pagecache page units; huge pages here.
     */
    static pgoff_t vma_hugecache_offset(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long address)
    {
    	return ((address - vma->vm_start) >> huge_page_shift(h)) +
    			(vma->vm_pgoff >> huge_page_order(h));
    }
    
    pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
    				     unsigned long address)
    {
    	return vma_hugecache_offset(hstate_vma(vma), vma, address);
    }
    EXPORT_SYMBOL_GPL(linear_hugepage_index);
    
    /*
     * Return the size of the pages allocated when backing a VMA. In the majority
     * cases this will be same size as used by the page table entries.
     */
    unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
    {
    	if (vma->vm_ops && vma->vm_ops->pagesize)
    		return vma->vm_ops->pagesize(vma);
    	return PAGE_SIZE;
    }
    EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
    
    /*
     * Return the page size being used by the MMU to back a VMA. In the majority
     * of cases, the page size used by the kernel matches the MMU size. On
     * architectures where it differs, an architecture-specific 'strong'
     * version of this symbol is required.
     */
    __weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
    {
    	return vma_kernel_pagesize(vma);
    }
    
    /*
     * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
     * bits of the reservation map pointer, which are always clear due to
     * alignment.
     */
    #define HPAGE_RESV_OWNER    (1UL << 0)
    #define HPAGE_RESV_UNMAPPED (1UL << 1)
    #define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED)
    
    /*
     * These helpers are used to track how many pages are reserved for
     * faults in a MAP_PRIVATE mapping. Only the process that called mmap()
     * is guaranteed to have their future faults succeed.
     *
     * With the exception of reset_vma_resv_huge_pages() which is called at fork(),
     * the reserve counters are updated with the hugetlb_lock held. It is safe
     * to reset the VMA at fork() time as it is not in use yet and there is no
     * chance of the global counters getting corrupted as a result of the values.
     *
     * The private mapping reservation is represented in a subtly different
     * manner to a shared mapping.  A shared mapping has a region map associated
     * with the underlying file, this region map represents the backing file
     * pages which have ever had a reservation assigned which this persists even
     * after the page is instantiated.  A private mapping has a region map
     * associated with the original mmap which is attached to all VMAs which
     * reference it, this region map represents those offsets which have consumed
     * reservation ie. where pages have been instantiated.
     */
    static unsigned long get_vma_private_data(struct vm_area_struct *vma)
    {
    	return (unsigned long)vma->vm_private_data;
    }
    
    static void set_vma_private_data(struct vm_area_struct *vma,
    							unsigned long value)
    {
    	vma->vm_private_data = (void *)value;
    }
    
    static void
    resv_map_set_hugetlb_cgroup_uncharge_info(struct resv_map *resv_map,
    					  struct hugetlb_cgroup *h_cg,
    					  struct hstate *h)
    {
    #ifdef CONFIG_CGROUP_HUGETLB
    	if (!h_cg || !h) {
    		resv_map->reservation_counter = NULL;
    		resv_map->pages_per_hpage = 0;
    		resv_map->css = NULL;
    	} else {
    		resv_map->reservation_counter =
    			&h_cg->rsvd_hugepage[hstate_index(h)];
    		resv_map->pages_per_hpage = pages_per_huge_page(h);
    		resv_map->css = &h_cg->css;
    	}
    #endif
    }
    
    struct resv_map *resv_map_alloc(void)
    {
    	struct resv_map *resv_map = kmalloc(sizeof(*resv_map), GFP_KERNEL);
    	struct file_region *rg = kmalloc(sizeof(*rg), GFP_KERNEL);
    
    	if (!resv_map || !rg) {
    		kfree(resv_map);
    		kfree(rg);
    		return NULL;
    	}
    
    	kref_init(&resv_map->refs);
    	spin_lock_init(&resv_map->lock);
    	INIT_LIST_HEAD(&resv_map->regions);
    
    	resv_map->adds_in_progress = 0;
    	/*
    	 * Initialize these to 0. On shared mappings, 0's here indicate these
    	 * fields don't do cgroup accounting. On private mappings, these will be
    	 * re-initialized to the proper values, to indicate that hugetlb cgroup
    	 * reservations are to be un-charged from here.
    	 */
    	resv_map_set_hugetlb_cgroup_uncharge_info(resv_map, NULL, NULL);
    
    	INIT_LIST_HEAD(&resv_map->region_cache);
    	list_add(&rg->link, &resv_map->region_cache);
    	resv_map->region_cache_count = 1;
    
    	return resv_map;
    }
    
    void resv_map_release(struct kref *ref)
    {
    	struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
    	struct list_head *head = &resv_map->region_cache;
    	struct file_region *rg, *trg;
    
    	/* Clear out any active regions before we release the map. */
    	region_del(resv_map, 0, LONG_MAX);
    
    	/* ... and any entries left in the cache */
    	list_for_each_entry_safe(rg, trg, head, link) {
    		list_del(&rg->link);
    		kfree(rg);
    	}
    
    	VM_BUG_ON(resv_map->adds_in_progress);
    
    	kfree(resv_map);
    }
    
    static inline struct resv_map *inode_resv_map(struct inode *inode)
    {
    	/*
    	 * At inode evict time, i_mapping may not point to the original
    	 * address space within the inode.  This original address space
    	 * contains the pointer to the resv_map.  So, always use the
    	 * address space embedded within the inode.
    	 * The VERY common case is inode->mapping == &inode->i_data but,
    	 * this may not be true for device special inodes.
    	 */
    	return (struct resv_map *)(&inode->i_data)->private_data;
    }
    
    static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
    {
    	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
    	if (vma->vm_flags & VM_MAYSHARE) {
    		struct address_space *mapping = vma->vm_file->f_mapping;
    		struct inode *inode = mapping->host;
    
    		return inode_resv_map(inode);
    
    	} else {
    		return (struct resv_map *)(get_vma_private_data(vma) &
    							~HPAGE_RESV_MASK);
    	}
    }
    
    static void set_vma_resv_map(struct vm_area_struct *vma, struct resv_map *map)
    {
    	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
    	VM_BUG_ON_VMA(vma->vm_flags & VM_MAYSHARE, vma);
    
    	set_vma_private_data(vma, (get_vma_private_data(vma) &
    				HPAGE_RESV_MASK) | (unsigned long)map);
    }
    
    static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags)
    {
    	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
    	VM_BUG_ON_VMA(vma->vm_flags & VM_MAYSHARE, vma);
    
    	set_vma_private_data(vma, get_vma_private_data(vma) | flags);
    }
    
    static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag)
    {
    	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
    
    	return (get_vma_private_data(vma) & flag) != 0;
    }
    
    /* Reset counters to 0 and clear all HPAGE_RESV_* flags */
    void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
    {
    	VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
    	if (!(vma->vm_flags & VM_MAYSHARE))
    		vma->vm_private_data = (void *)0;
    }
    
    /* Returns true if the VMA has associated reserve pages */
    static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
    {
    	if (vma->vm_flags & VM_NORESERVE) {
    		/*
    		 * This address is already reserved by other process(chg == 0),
    		 * so, we should decrement reserved count. Without decrementing,
    		 * reserve count remains after releasing inode, because this
    		 * allocated page will go into page cache and is regarded as
    		 * coming from reserved pool in releasing step.  Currently, we
    		 * don't have any other solution to deal with this situation
    		 * properly, so add work-around here.
    		 */
    		if (vma->vm_flags & VM_MAYSHARE && chg == 0)
    			return true;
    		else
    			return false;
    	}
    
    	/* Shared mappings always use reserves */
    	if (vma->vm_flags & VM_MAYSHARE) {
    		/*
    		 * We know VM_NORESERVE is not set.  Therefore, there SHOULD
    		 * be a region map for all pages.  The only situation where
    		 * there is no region map is if a hole was punched via
    		 * fallocate.  In this case, there really are no reserves to
    		 * use.  This situation is indicated if chg != 0.
    		 */
    		if (chg)
    			return false;
    		else
    			return true;
    	}
    
    	/*
    	 * Only the process that called mmap() has reserves for
    	 * private mappings.
    	 */
    	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
    		/*
    		 * Like the shared case above, a hole punch or truncate
    		 * could have been performed on the private mapping.
    		 * Examine the value of chg to determine if reserves
    		 * actually exist or were previously consumed.
    		 * Very Subtle - The value of chg comes from a previous
    		 * call to vma_needs_reserves().  The reserve map for
    		 * private mappings has different (opposite) semantics
    		 * than that of shared mappings.  vma_needs_reserves()
    		 * has already taken this difference in semantics into
    		 * account.  Therefore, the meaning of chg is the same
    		 * as in the shared case above.  Code could easily be
    		 * combined, but keeping it separate draws attention to
    		 * subtle differences.
    		 */
    		if (chg)
    			return false;
    		else
    			return true;
    	}
    
    	return false;
    }
    
    static void enqueue_huge_page(struct hstate *h, struct page *page)
    {
    	int nid = page_to_nid(page);
    	list_move(&page->lru, &h->hugepage_freelists[nid]);
    	h->free_huge_pages++;
    	h->free_huge_pages_node[nid]++;
    	SetPageHugeFreed(page);
    }
    
    static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
    {
    	struct page *page;
    	bool nocma = !!(current->flags & PF_MEMALLOC_NOCMA);
    
    	list_for_each_entry(page, &h->hugepage_freelists[nid], lru) {
    		if (nocma && is_migrate_cma_page(page))
    			continue;
    
    		if (PageHWPoison(page))
    			continue;
    
    		list_move(&page->lru, &h->hugepage_activelist);
    		set_page_refcounted(page);
    		ClearPageHugeFreed(page);
    		h->free_huge_pages--;
    		h->free_huge_pages_node[nid]--;
    		return page;
    	}
    
    	return NULL;
    }
    
    static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask, int nid,
    		nodemask_t *nmask)
    {
    	unsigned int cpuset_mems_cookie;
    	struct zonelist *zonelist;
    	struct zone *zone;
    	struct zoneref *z;
    	int node = NUMA_NO_NODE;
    
    	zonelist = node_zonelist(nid, gfp_mask);
    
    retry_cpuset:
    	cpuset_mems_cookie = read_mems_allowed_begin();
    	for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nmask) {
    		struct page *page;
    
    		if (!cpuset_zone_allowed(zone, gfp_mask))
    			continue;
    		/*
    		 * no need to ask again on the same node. Pool is node rather than
    		 * zone aware
    		 */
    		if (zone_to_nid(zone) == node)
    			continue;
    		node = zone_to_nid(zone);
    
    		page = dequeue_huge_page_node_exact(h, node);
    		if (page)
    			return page;
    	}
    	if (unlikely(read_mems_allowed_retry(cpuset_mems_cookie)))
    		goto retry_cpuset;
    
    	return NULL;
    }
    
    static struct page *dequeue_huge_page_vma(struct hstate *h,
    				struct vm_area_struct *vma,
    				unsigned long address, int avoid_reserve,
    				long chg)
    {
    	struct page *page;
    	struct mempolicy *mpol;
    	gfp_t gfp_mask;
    	nodemask_t *nodemask;
    	int nid;
    
    	/*
    	 * A child process with MAP_PRIVATE mappings created by their parent
    	 * have no page reserves. This check ensures that reservations are
    	 * not "stolen". The child may still get SIGKILLed
    	 */
    	if (!vma_has_reserves(vma, chg) &&
    			h->free_huge_pages - h->resv_huge_pages == 0)
    		goto err;
    
    	/* If reserves cannot be used, ensure enough pages are in the pool */
    	if (avoid_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
    		goto err;
    
    	gfp_mask = htlb_alloc_mask(h);
    	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
    	page = dequeue_huge_page_nodemask(h, gfp_mask, nid, nodemask);
    	if (page && !avoid_reserve && vma_has_reserves(vma, chg)) {
    		SetPagePrivate(page);
    		h->resv_huge_pages--;
    	}
    
    	mpol_cond_put(mpol);
    	return page;
    
    err:
    	return NULL;
    }
    
    /*
     * common helper functions for hstate_next_node_to_{alloc|free}.
     * We may have allocated or freed a huge page based on a different
     * nodes_allowed previously, so h->next_node_to_{alloc|free} might
     * be outside of *nodes_allowed.  Ensure that we use an allowed
     * node for alloc or free.
     */
    static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
    {
    	nid = next_node_in(nid, *nodes_allowed);
    	VM_BUG_ON(nid >= MAX_NUMNODES);
    
    	return nid;
    }
    
    static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
    {
    	if (!node_isset(nid, *nodes_allowed))
    		nid = next_node_allowed(nid, nodes_allowed);
    	return nid;
    }
    
    /*
     * returns the previously saved node ["this node"] from which to
     * allocate a persistent huge page for the pool and advance the
     * next node from which to allocate, handling wrap at end of node
     * mask.
     */
    static int hstate_next_node_to_alloc(struct hstate *h,
    					nodemask_t *nodes_allowed)
    {
    	int nid;
    
    	VM_BUG_ON(!nodes_allowed);
    
    	nid = get_valid_node_allowed(h->next_nid_to_alloc, nodes_allowed);
    	h->next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
    
    	return nid;
    }
    
    /*
     * helper for free_pool_huge_page() - return the previously saved
     * node ["this node"] from which to free a huge page.  Advance the
     * next node id whether or not we find a free huge page to free so
     * that the next attempt to free addresses the next node.
     */
    static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
    {
    	int nid;
    
    	VM_BUG_ON(!nodes_allowed);
    
    	nid = get_valid_node_allowed(h->next_nid_to_free, nodes_allowed);
    	h->next_nid_to_free = next_node_allowed(nid, nodes_allowed);
    
    	return nid;
    }
    
    #define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask)		\
    	for (nr_nodes = nodes_weight(*mask);				\
    		nr_nodes > 0 &&						\
    		((node = hstate_next_node_to_alloc(hs, mask)) || 1);	\
    		nr_nodes--)
    
    #define for_each_node_mask_to_free(hs, nr_nodes, node, mask)		\
    	for (nr_nodes = nodes_weight(*mask);				\
    		nr_nodes > 0 &&						\
    		((node = hstate_next_node_to_free(hs, mask)) || 1);	\
    		nr_nodes--)
    
    #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
    static void destroy_compound_gigantic_page(struct page *page,
    					unsigned int order)
    {
    	int i;
    	int nr_pages = 1 << order;
    	struct page *p = page + 1;
    
    	atomic_set(compound_mapcount_ptr(page), 0);
    	if (hpage_pincount_available(page))
    		atomic_set(compound_pincount_ptr(page), 0);
    
    	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
    		clear_compound_head(p);
    		set_page_refcounted(p);
    	}
    
    	set_compound_order(page, 0);
    	page[1].compound_nr = 0;
    	__ClearPageHead(page);
    }
    
    static void free_gigantic_page(struct page *page, unsigned int order)
    {
    	/*
    	 * If the page isn't allocated using the cma allocator,
    	 * cma_release() returns false.
    	 */
    #ifdef CONFIG_CMA
    	if (cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order))
    		return;
    #endif
    
    	free_contig_range(page_to_pfn(page), 1 << order);
    }
    
    #ifdef CONFIG_CONTIG_ALLOC
    static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
    		int nid, nodemask_t *nodemask)
    {
    	unsigned long nr_pages = 1UL << huge_page_order(h);
    	if (nid == NUMA_NO_NODE)
    		nid = numa_mem_id();
    
    #ifdef CONFIG_CMA
    	{
    		struct page *page;
    		int node;
    
    		if (hugetlb_cma[nid]) {
    			page = cma_alloc(hugetlb_cma[nid], nr_pages,
    					huge_page_order(h), true);
    			if (page)
    				return page;
    		}
    
    		if (!(gfp_mask & __GFP_THISNODE)) {
    			for_each_node_mask(node, *nodemask) {
    				if (node == nid || !hugetlb_cma[node])
    					continue;
    
    				page = cma_alloc(hugetlb_cma[node], nr_pages,
    						huge_page_order(h), true);
    				if (page)
    					return page;
    			}
    		}
    	}
    #endif
    
    	return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
    }
    
    static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
    static void prep_compound_gigantic_page(struct page *page, unsigned int order);
    #else /* !CONFIG_CONTIG_ALLOC */
    static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
    					int nid, nodemask_t *nodemask)
    {
    	return NULL;
    }
    #endif /* CONFIG_CONTIG_ALLOC */
    
    #else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE */
    static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
    					int nid, nodemask_t *nodemask)
    {
    	return NULL;
    }
    static inline void free_gigantic_page(struct page *page, unsigned int order) { }
    static inline void destroy_compound_gigantic_page(struct page *page,
    						unsigned int order) { }
    #endif
    
    static void update_and_free_page(struct hstate *h, struct page *page)
    {
    	int i;
    
    	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
    		return;
    
    	h->nr_huge_pages--;
    	h->nr_huge_pages_node[page_to_nid(page)]--;
    	for (i = 0; i < pages_per_huge_page(h); i++) {
    		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
    				1 << PG_referenced | 1 << PG_dirty |
    				1 << PG_active | 1 << PG_private |
    				1 << PG_writeback);
    	}
    	VM_BUG_ON_PAGE(hugetlb_cgroup_from_page(page), page);
    	VM_BUG_ON_PAGE(hugetlb_cgroup_from_page_rsvd(page), page);
    	set_compound_page_dtor(page, NULL_COMPOUND_DTOR);
    	set_page_refcounted(page);
    	if (hstate_is_gigantic(h)) {
    		/*
    		 * Temporarily drop the hugetlb_lock, because
    		 * we might block in free_gigantic_page().
    		 */
    		spin_unlock(&hugetlb_lock);
    		destroy_compound_gigantic_page(page, huge_page_order(h));
    		free_gigantic_page(page, huge_page_order(h));
    		spin_lock(&hugetlb_lock);
    	} else {
    		__free_pages(page, huge_page_order(h));
    	}
    }
    
    struct hstate *size_to_hstate(unsigned long size)
    {
    	struct hstate *h;
    
    	for_each_hstate(h) {
    		if (huge_page_size(h) == size)
    			return h;
    	}
    	return NULL;
    }
    
    /*
     * Test to determine whether the hugepage is "active/in-use" (i.e. being linked
     * to hstate->hugepage_activelist.)
     *
     * This function can be called for tail pages, but never returns true for them.
     */
    bool page_huge_active(struct page *page)
    {
    	return PageHeadHuge(page) && PagePrivate(&page[1]);
    }
    
    /* never called for tail page */
    void set_page_huge_active(struct page *page)
    {
    	VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
    	SetPagePrivate(&page[1]);
    }
    
    static void clear_page_huge_active(struct page *page)
    {
    	VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
    	ClearPagePrivate(&page[1]);
    }
    
    /*
     * Internal hugetlb specific page flag. Do not use outside of the hugetlb
     * code
     */
    static inline bool PageHugeTemporary(struct page *page)
    {
    	if (!PageHuge(page))
    		return false;
    
    	return (unsigned long)page[2].mapping == -1U;
    }
    
    static inline void SetPageHugeTemporary(struct page *page)
    {
    	page[2].mapping = (void *)-1U;
    }
    
    static inline void ClearPageHugeTemporary(struct page *page)
    {
    	page[2].mapping = NULL;
    }
    
    static void __free_huge_page(struct page *page)
    {
    	/*
    	 * Can't pass hstate in here because it is called from the
    	 * compound page destructor.
    	 */
    	struct hstate *h = page_hstate(page);
    	int nid = page_to_nid(page);
    	struct hugepage_subpool *spool =
    		(struct hugepage_subpool *)page_private(page);
    	bool restore_reserve;
    
    	VM_BUG_ON_PAGE(page_count(page), page);
    	VM_BUG_ON_PAGE(page_mapcount(page), page);
    
    	set_page_private(page, 0);
    	page->mapping = NULL;
    	restore_reserve = PagePrivate(page);
    	ClearPagePrivate(page);
    
    	/*
    	 * If PagePrivate() was set on page, page allocation consumed a
    	 * reservation.  If the page was associated with a subpool, there
    	 * would have been a page reserved in the subpool before allocation
    	 * via hugepage_subpool_get_pages().  Since we are 'restoring' the
    	 * reservtion, do not call hugepage_subpool_put_pages() as this will
    	 * remove the reserved page from the subpool.
    	 */
    	if (!restore_reserve) {
    		/*
    		 * A return code of zero implies that the subpool will be
    		 * under its minimum size if the reservation is not restored
    		 * after page is free.  Therefore, force restore_reserve
    		 * operation.
    		 */
    		if (hugepage_subpool_put_pages(spool, 1) == 0)
    			restore_reserve = true;
    	}
    
    	spin_lock(&hugetlb_lock);
    	clear_page_huge_active(page);
    	hugetlb_cgroup_uncharge_page(hstate_index(h),
    				     pages_per_huge_page(h), page);
    	hugetlb_cgroup_uncharge_page_rsvd(hstate_index(h),
    					  pages_per_huge_page(h), page);
    	if (restore_reserve)
    		h->resv_huge_pages++;
    
    	if (PageHugeTemporary(page)) {
    		list_del(&page->lru);
    		ClearPageHugeTemporary(page);
    		update_and_free_page(h, page);
    	} else if (h->surplus_huge_pages_node[nid]) {
    		/* remove the page from active list */
    		list_del(&page->lru);
    		update_and_free_page(h, page);
    		h->surplus_huge_pages--;
    		h->surplus_huge_pages_node[nid]--;
    	} else {
    		arch_clear_hugepage_flags(page);
    		enqueue_huge_page(h, page);
    	}
    	spin_unlock(&hugetlb_lock);
    }
    
    /*
     * As free_huge_page() can be called from a non-task context, we have
     * to defer the actual freeing in a workqueue to prevent potential
     * hugetlb_lock deadlock.
     *
     * free_hpage_workfn() locklessly retrieves the linked list of pages to
     * be freed and frees them one-by-one. As the page->mapping pointer is
     * going to be cleared in __free_huge_page() anyway, it is reused as the
     * llist_node structure of a lockless linked list of huge pages to be freed.
     */
    static LLIST_HEAD(hpage_freelist);
    
    static void free_hpage_workfn(struct work_struct *work)
    {
    	struct llist_node *node;
    	struct page *page;
    
    	node = llist_del_all(&hpage_freelist);
    
    	while (node) {
    		page = container_of((struct address_space **)node,
    				     struct page, mapping);
    		node = node->next;
    		__free_huge_page(page);
    	}
    }
    static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
    
    void free_huge_page(struct page *page)
    {
    	/*
    	 * Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
    	 */
    	if (!in_task()) {
    		/*
    		 * Only call schedule_work() if hpage_freelist is previously
    		 * empty. Otherwise, schedule_work() had been called but the
    		 * workfn hasn't retrieved the list yet.
    		 */
    		if (llist_add((struct llist_node *)&page->mapping,
    			      &hpage_freelist))
    			schedule_work(&free_hpage_work);
    		return;
    	}
    
    	__free_huge_page(page);
    }
    
    static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
    {
    	INIT_LIST_HEAD(&page->lru);
    	set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
    	set_hugetlb_cgroup(page, NULL);
    	set_hugetlb_cgroup_rsvd(page, NULL);
    	spin_lock(&hugetlb_lock);
    	h->nr_huge_pages++;
    	h->nr_huge_pages_node[nid]++;
    	ClearPageHugeFreed(page);
    	spin_unlock(&hugetlb_lock);
    }
    
    static void prep_compound_gigantic_page(struct page *page, unsigned int order)
    {
    	int i;
    	int nr_pages = 1 << order;
    	struct page *p = page + 1;
    
    	/* we rely on prep_new_huge_page to set the destructor */
    	set_compound_order(page, order);
    	__ClearPageReserved(page);
    	__SetPageHead(page);
    	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
    		/*
    		 * For gigantic hugepages allocated through bootmem at
    		 * boot, it's safer to be consistent with the not-gigantic
    		 * hugepages and clear the PG_reserved bit from all tail pages
    		 * too.  Otherwise drivers using get_user_pages() to access tail
    		 * pages may get the reference counting wrong if they see
    		 * PG_reserved set on a tail page (despite the head page not
    		 * having PG_reserved set).  Enforcing this consistency between
    		 * head and tail pages allows drivers to optimize away a check
    		 * on the head page when they need know if put_page() is needed
    		 * after get_user_pages().
    		 */
    		__ClearPageReserved(p);
    		set_page_count(p, 0);
    		set_compound_head(p, page);
    	}
    	atomic_set(compound_mapcount_ptr(page), -1);
    
    	if (hpage_pincount_available(page))
    		atomic_set(compound_pincount_ptr(page), 0);
    }
    
    /*
     * PageHuge() only returns true for hugetlbfs pages, but not for normal or
     * transparent huge pages.  See the PageTransHuge() documentation for more
     * details.
     */
    int PageHuge(struct page *page)
    {
    	if (!PageCompound(page))
    		return 0;
    
    	page = compound_head(page);
    	return page[1].compound_dtor == HUGETLB_PAGE_DTOR;
    }
    EXPORT_SYMBOL_GPL(PageHuge);
    
    /*
     * PageHeadHuge() only returns true for hugetlbfs head page, but not for
     * normal or transparent huge pages.
     */
    int PageHeadHuge(struct page *page_head)
    {
    	if (!PageHead(page_head))
    		return 0;
    
    	return page_head[1].compound_dtor == HUGETLB_PAGE_DTOR;
    }
    
    /*
     * Find and lock address space (mapping) in write mode.
     *
     * Upon entry, the page is locked which means that page_mapping() is
     * stable.  Due to locking order, we can only trylock_write.  If we can
     * not get the lock, simply return NULL to caller.
     */
    struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage)
    {
    	struct address_space *mapping = page_mapping(hpage);
    
    	if (!mapping)
    		return mapping;
    
    	if (i_mmap_trylock_write(mapping))
    		return mapping;
    
    	return NULL;
    }
    
    pgoff_t __basepage_index(struct page *page)
    {
    	struct page *page_head = compound_head(page);
    	pgoff_t index = page_index(page_head);
    	unsigned long compound_idx;
    
    	if (!PageHuge(page_head))
    		return page_index(page);
    
    	if (compound_order(page_head) >= MAX_ORDER)
    		compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
    	else
    		compound_idx = page - page_head;
    
    	return (index << compound_order(page_head)) + compound_idx;
    }
    
    static struct page *alloc_buddy_huge_page(struct hstate *h,
    		gfp_t gfp_mask, int nid, nodemask_t *nmask,
    		nodemask_t *node_alloc_noretry)
    {
    	int order = huge_page_order(h);
    	struct page *page;
    	bool alloc_try_hard = true;
    
    	/*
    	 * By default we always try hard to allocate the page with
    	 * __GFP_RETRY_MAYFAIL flag.  However, if we are allocating pages in
    	 * a loop (to adjust global huge page counts) and previous allocation
    	 * failed, do not continue to try hard on the same node.  Use the
    	 * node_alloc_noretry bitmap to manage this state information.
    	 */
    	if (node_alloc_noretry && node_isset(nid, *node_alloc_noretry))
    		alloc_try_hard = false;
    	gfp_mask |= __GFP_COMP|__GFP_NOWARN;
    	if (alloc_try_hard)
    		gfp_mask |= __GFP_RETRY_MAYFAIL;
    	if (nid == NUMA_NO_NODE)
    		nid = numa_mem_id();
    	page = __alloc_pages_nodemask(gfp_mask, order, nid, nmask);
    	if (page)
    		__count_vm_event(HTLB_BUDDY_PGALLOC);
    	else
    		__count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
    
    	/*
    	 * If we did not specify __GFP_RETRY_MAYFAIL, but still got a page this
    	 * indicates an overall state change.  Clear bit so that we resume
    	 * normal 'try hard' allocations.
    	 */
    	if (node_alloc_noretry && page && !alloc_try_hard)
    		node_clear(nid, *node_alloc_noretry);
    
    	/*
    	 * If we tried hard to get a page but failed, set bit so that
    	 * subsequent attempts will not try as hard until there is an
    	 * overall state change.
    	 */
    	if (node_alloc_noretry && !page && alloc_try_hard)
    		node_set(nid, *node_alloc_noretry);
    
    	return page;
    }
    
    /*
     * Common helper to allocate a fresh hugetlb page. All specific allocators
     * should use this function to get new hugetlb pages
     */
    static struct page *alloc_fresh_huge_page(struct hstate *h,
    		gfp_t gfp_mask, int nid, nodemask_t *nmask,
    		nodemask_t *node_alloc_noretry)
    {
    	struct page *page;
    
    	if (hstate_is_gigantic(h))
    		page = alloc_gigantic_page(h, gfp_mask, nid, nmask);
    	else
    		page = alloc_buddy_huge_page(h, gfp_mask,
    				nid, nmask, node_alloc_noretry);
    	if (!page)
    		return NULL;
    
    	if (hstate_is_gigantic(h))
    		prep_compound_gigantic_page(page, huge_page_order(h));
    	prep_new_huge_page(h, page, page_to_nid(page));
    
    	return page;
    }
    
    /*
     * Allocates a fresh page to the hugetlb allocator pool in the node interleaved
     * manner.
     */
    static int alloc_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
    				nodemask_t *node_alloc_noretry)
    {
    	struct page *page;
    	int nr_nodes, node;
    	gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
    
    	for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
    		page = alloc_fresh_huge_page(h, gfp_mask, node, nodes_allowed,
    						node_alloc_noretry);
    		if (page)
    			break;
    	}
    
    	if (!page)
    		return 0;
    
    	put_page(page); /* free it into the hugepage allocator */
    
    	return 1;
    }
    
    /*
     * Free huge page from pool from next node to free.
     * Attempt to keep persistent huge pages more or less
     * balanced over allowed nodes.
     * Called with hugetlb_lock locked.
     */
    static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
    							 bool acct_surplus)
    {
    	int nr_nodes, node;
    	int ret = 0;
    
    	for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
    		/*
    		 * If we're returning unused surplus pages, only examine
    		 * nodes with surplus pages.
    		 */
    		if ((!acct_surplus || h->surplus_huge_pages_node[node]) &&
    		    !list_empty(&h->hugepage_freelists[node])) {
    			struct page *page =
    				list_entry(h->hugepage_freelists[node].next,
    					  struct page, lru);
    			list_del(&page->lru);
    			h->free_huge_pages--;
    			h->free_huge_pages_node[node]--;
    			if (acct_surplus) {
    				h->surplus_huge_pages--;
    				h->surplus_huge_pages_node[node]--;
    			}
    			update_and_free_page(h, page);
    			ret = 1;
    			break;
    		}
    	}
    
    	return ret;
    }
    
    /*
     * Dissolve a given free hugepage into free buddy pages. This function does
     * nothing for in-use hugepages and non-hugepages.
     * This function returns values like below:
     *
     *  -EBUSY: failed to dissolved free hugepages or the hugepage is in-use
     *          (allocated or reserved.)
     *       0: successfully dissolved free hugepages or the page is not a
     *          hugepage (considered as already dissolved)
     */
    int dissolve_free_huge_page(struct page *page)
    {
    	int rc = -EBUSY;
    
    retry:
    	/* Not to disrupt normal path by vainly holding hugetlb_lock */
    	if (!PageHuge(page))
    		return 0;
    
    	spin_lock(&hugetlb_lock);
    	if (!PageHuge(page)) {
    		rc = 0;
    		goto out;
    	}
    
    	if (!page_count(page)) {
    		struct page *head = compound_head(page);
    		struct hstate *h = page_hstate(head);
    		int nid = page_to_nid(head);
    		if (h->free_huge_pages - h->resv_huge_pages == 0)
    			goto out;
    
    		/*
    		 * We should make sure that the page is already on the free list
    		 * when it is dissolved.
    		 */
    		if (unlikely(!PageHugeFreed(head))) {
    			spin_unlock(&hugetlb_lock);
    			cond_resched();
    
    			/*
    			 * Theoretically, we should return -EBUSY when we
    			 * encounter this race. In fact, we have a chance
    			 * to successfully dissolve the page if we do a
    			 * retry. Because the race window is quite small.
    			 * If we seize this opportunity, it is an optimization
    			 * for increasing the success rate of dissolving page.
    			 */
    			goto retry;
    		}
    
    		/*
    		 * Move PageHWPoison flag from head page to the raw error page,
    		 * which makes any subpages rather than the error page reusable.
    		 */
    		if (PageHWPoison(head) && page != head) {
    			SetPageHWPoison(page);
    			ClearPageHWPoison(head);
    		}
    		list_del(&head->lru);
    		h->free_huge_pages--;
    		h->free_huge_pages_node[nid]--;
    		h->max_huge_pages--;
    		update_and_free_page(h, head);
    		rc = 0;
    	}
    out:
    	spin_unlock(&hugetlb_lock);
    	return rc;
    }
    
    /*
     * Dissolve free hugepages in a given pfn range. Used by memory hotplug to
     * make specified memory blocks removable from the system.
     * Note that this will dissolve a free gigantic hugepage completely, if any
     * part of it lies within the given range.
     * Also note that if dissolve_free_huge_page() returns with an error, all
     * free hugepages that were dissolved before that error are lost.
     */
    int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
    {
    	unsigned long pfn;
    	struct page *page;
    	int rc = 0;
    
    	if (!hugepages_supported())
    		return rc;
    
    	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
    		page = pfn_to_page(pfn);
    		rc = dissolve_free_huge_page(page);
    		if (rc)
    			break;
    	}
    
    	return rc;
    }
    
    /*
     * Allocates a fresh surplus page from the page allocator.
     */
    static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
    		int nid, nodemask_t *nmask)
    {
    	struct page *page = NULL;
    
    	if (hstate_is_gigantic(h))
    		return NULL;
    
    	spin_lock(&hugetlb_lock);
    	if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages)
    		goto out_unlock;
    	spin_unlock(&hugetlb_lock);
    
    	page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL);
    	if (!page)
    		return NULL;
    
    	spin_lock(&hugetlb_lock);
    	/*
    	 * We could have raced with the pool size change.
    	 * Double check that and simply deallocate the new page
    	 * if we would end up overcommiting the surpluses. Abuse
    	 * temporary page to workaround the nasty free_huge_page
    	 * codeflow
    	 */
    	if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
    		SetPageHugeTemporary(page);
    		spin_unlock(&hugetlb_lock);
    		put_page(page);
    		return NULL;
    	} else {
    		h->surplus_huge_pages++;
    		h->surplus_huge_pages_node[page_to_nid(page)]++;
    	}
    
    out_unlock:
    	spin_unlock(&hugetlb_lock);
    
    	return page;
    }
    
    static struct page *alloc_migrate_huge_page(struct hstate *h, gfp_t gfp_mask,
    				     int nid, nodemask_t *nmask)
    {
    	struct page *page;
    
    	if (hstate_is_gigantic(h))
    		return NULL;
    
    	page = alloc_fresh_huge_page(h, gfp_mask, nid, nmask, NULL);
    	if (!page)
    		return NULL;
    
    	/*
    	 * We do not account these pages as surplus because they are only
    	 * temporary and will be released properly on the last reference
    	 */
    	SetPageHugeTemporary(page);
    
    	return page;
    }
    
    /*
     * Use the VMA's mpolicy to allocate a huge page from the buddy.
     */
    static
    struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
    		struct vm_area_struct *vma, unsigned long addr)
    {
    	struct page *page;
    	struct mempolicy *mpol;
    	gfp_t gfp_mask = htlb_alloc_mask(h);
    	int nid;
    	nodemask_t *nodemask;
    
    	nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask);
    	page = alloc_surplus_huge_page(h, gfp_mask, nid, nodemask);
    	mpol_cond_put(mpol);
    
    	return page;
    }
    
    /* page migration callback function */
    struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
    		nodemask_t *nmask, gfp_t gfp_mask)
    {
    	spin_lock(&hugetlb_lock);
    	if (h->free_huge_pages - h->resv_huge_pages > 0) {
    		struct page *page;
    
    		page = dequeue_huge_page_nodemask(h, gfp_mask, preferred_nid, nmask);
    		if (page) {
    			spin_unlock(&hugetlb_lock);
    			return page;
    		}
    	}
    	spin_unlock(&hugetlb_lock);
    
    	return alloc_migrate_huge_page(h, gfp_mask, preferred_nid, nmask);
    }
    
    /* mempolicy aware migration callback */
    struct page *alloc_huge_page_vma(struct hstate *h, struct vm_area_struct *vma,
    		unsigned long address)
    {
    	struct mempolicy *mpol;
    	nodemask_t *nodemask;
    	struct page *page;
    	gfp_t gfp_mask;
    	int node;
    
    	gfp_mask = htlb_alloc_mask(h);
    	node = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
    	page = alloc_huge_page_nodemask(h, node, nodemask, gfp_mask);
    	mpol_cond_put(mpol);
    
    	return page;
    }
    
    /*
     * Increase the hugetlb pool such that it can accommodate a reservation
     * of size 'delta'.
     */
    static int gather_surplus_pages(struct hstate *h, long delta)
    	__must_hold(&hugetlb_lock)
    {
    	struct list_head surplus_list;
    	struct page *page, *tmp;
    	int ret;
    	long i;
    	long needed, allocated;
    	bool alloc_ok = true;
    
    	needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
    	if (needed <= 0) {
    		h->resv_huge_pages += delta;
    		return 0;
    	}
    
    	allocated = 0;
    	INIT_LIST_HEAD(&surplus_list);
    
    	ret = -ENOMEM;
    retry:
    	spin_unlock(&hugetlb_lock);
    	for (i = 0; i < needed; i++) {
    		page = alloc_surplus_huge_page(h, htlb_alloc_mask(h),
    				NUMA_NO_NODE, NULL);
    		if (!page) {
    			alloc_ok = false;
    			break;
    		}
    		list_add(&page->lru, &surplus_list);
    		cond_resched();
    	}
    	allocated += i;
    
    	/*
    	 * After retaking hugetlb_lock, we need to recalculate 'needed'
    	 * because either resv_huge_pages or free_huge_pages may have changed.
    	 */
    	spin_lock(&hugetlb_lock);
    	needed = (h->resv_huge_pages + delta) -
    			(h->free_huge_pages + allocated);
    	if (needed > 0) {
    		if (alloc_ok)
    			goto retry;
    		/*
    		 * We were not able to allocate enough pages to
    		 * satisfy the entire reservation so we free what
    		 * we've allocated so far.
    		 */
    		goto free;
    	}
    	/*
    	 * The surplus_list now contains _at_least_ the number of extra pages
    	 * needed to accommodate the reservation.  Add the appropriate number
    	 * of pages to the hugetlb pool and free the extras back to the buddy
    	 * allocator.  Commit the entire reservation here to prevent another
    	 * process from stealing the pages as they are added to the pool but
    	 * before they are reserved.
    	 */
    	needed += allocated;
    	h->resv_huge_pages += delta;
    	ret = 0;
    
    	/* Free the needed pages to the hugetlb pool */
    	list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
    		int zeroed;
    
    		if ((--needed) < 0)
    			break;
    		/*
    		 * This page is now managed by the hugetlb allocator and has
    		 * no users -- drop the buddy allocator's reference.
    		 */
    		zeroed = put_page_testzero(page);
    		VM_BUG_ON_PAGE(!zeroed, page);
    		enqueue_huge_page(h, page);
    	}
    free:
    	spin_unlock(&hugetlb_lock);
    
    	/* Free unnecessary surplus pages to the buddy allocator */
    	list_for_each_entry_safe(page, tmp, &surplus_list, lru)
    		put_page(page);
    	spin_lock(&hugetlb_lock);
    
    	return ret;
    }
    
    /*
     * This routine has two main purposes:
     * 1) Decrement the reservation count (resv_huge_pages) by the value passed
     *    in unused_resv_pages.  This corresponds to the prior adjustments made
     *    to the associated reservation map.
     * 2) Free any unused surplus pages that may have been allocated to satisfy
     *    the reservation.  As many as unused_resv_pages may be freed.
     *
     * Called with hugetlb_lock held.  However, the lock could be dropped (and
     * reacquired) during calls to cond_resched_lock.  Whenever dropping the lock,
     * we must make sure nobody else can claim pages we are in the process of
     * freeing.  Do this by ensuring resv_huge_page always is greater than the
     * number of huge pages we plan to free when dropping the lock.
     */
    static void return_unused_surplus_pages(struct hstate *h,
    					unsigned long unused_resv_pages)
    {
    	unsigned long nr_pages;
    
    	/* Cannot return gigantic pages currently */
    	if (hstate_is_gigantic(h))
    		goto out;
    
    	/*
    	 * Part (or even all) of the reservation could have been backed
    	 * by pre-allocated pages. Only free surplus pages.
    	 */
    	nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
    
    	/*
    	 * We want to release as many surplus pages as possible, spread
    	 * evenly across all nodes with memory. Iterate across these nodes
    	 * until we can no longer free unreserved surplus pages. This occurs
    	 * when the nodes with surplus pages have no free pages.
    	 * free_pool_huge_page() will balance the freed pages across the
    	 * on-line nodes with memory and will handle the hstate accounting.
    	 *
    	 * Note that we decrement resv_huge_pages as we free the pages.  If
    	 * we drop the lock, resv_huge_pages will still be sufficiently large
    	 * to cover subsequent pages we may free.
    	 */
    	while (nr_pages--) {
    		h->resv_huge_pages--;
    		unused_resv_pages--;
    		if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
    			goto out;
    		cond_resched_lock(&hugetlb_lock);
    	}
    
    out:
    	/* Fully uncommit the reservation */
    	h->resv_huge_pages -= unused_resv_pages;
    }
    
    
    /*
     * vma_needs_reservation, vma_commit_reservation and vma_end_reservation
     * are used by the huge page allocation routines to manage reservations.
     *
     * vma_needs_reservation is called to determine if the huge page at addr
     * within the vma has an associated reservation.  If a reservation is
     * needed, the value 1 is returned.  The caller is then responsible for
     * managing the global reservation and subpool usage counts.  After
     * the huge page has been allocated, vma_commit_reservation is called
     * to add the page to the reservation map.  If the page allocation fails,
     * the reservation must be ended instead of committed.  vma_end_reservation
     * is called in such cases.
     *
     * In the normal case, vma_commit_reservation returns the same value
     * as the preceding vma_needs_reservation call.  The only time this
     * is not the case is if a reserve map was changed between calls.  It
     * is the responsibility of the caller to notice the difference and
     * take appropriate action.
     *
     * vma_add_reservation is used in error paths where a reservation must
     * be restored when a newly allocated huge page must be freed.  It is
     * to be called after calling vma_needs_reservation to determine if a
     * reservation exists.
     */
    enum vma_resv_mode {
    	VMA_NEEDS_RESV,
    	VMA_COMMIT_RESV,
    	VMA_END_RESV,
    	VMA_ADD_RESV,
    };
    static long __vma_reservation_common(struct hstate *h,
    				struct vm_area_struct *vma, unsigned long addr,
    				enum vma_resv_mode mode)
    {
    	struct resv_map *resv;
    	pgoff_t idx;
    	long ret;
    	long dummy_out_regions_needed;
    
    	resv = vma_resv_map(vma);
    	if (!resv)
    		return 1;
    
    	idx = vma_hugecache_offset(h, vma, addr);
    	switch (mode) {
    	case VMA_NEEDS_RESV:
    		ret = region_chg(resv, idx, idx + 1, &dummy_out_regions_needed);
    		/* We assume that vma_reservation_* routines always operate on
    		 * 1 page, and that adding to resv map a 1 page entry can only
    		 * ever require 1 region.
    		 */
    		VM_BUG_ON(dummy_out_regions_needed != 1);
    		break;
    	case VMA_COMMIT_RESV:
    		ret = region_add(resv, idx, idx + 1, 1, NULL, NULL);
    		/* region_add calls of range 1 should never fail. */
    		VM_BUG_ON(ret < 0);
    		break;
    	case VMA_END_RESV:
    		region_abort(resv, idx, idx + 1, 1);
    		ret = 0;
    		break;
    	case VMA_ADD_RESV:
    		if (vma->vm_flags & VM_MAYSHARE) {
    			ret = region_add(resv, idx, idx + 1, 1, NULL, NULL);
    			/* region_add calls of range 1 should never fail. */
    			VM_BUG_ON(ret < 0);
    		} else {
    			region_abort(resv, idx, idx + 1, 1);
    			ret = region_del(resv, idx, idx + 1);
    		}
    		break;
    	default:
    		BUG();
    	}
    
    	if (vma->vm_flags & VM_MAYSHARE)
    		return ret;
    	else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && ret >= 0) {
    		/*
    		 * In most cases, reserves always exist for private mappings.
    		 * However, a file associated with mapping could have been
    		 * hole punched or truncated after reserves were consumed.
    		 * As subsequent fault on such a range will not use reserves.
    		 * Subtle - The reserve map for private mappings has the
    		 * opposite meaning than that of shared mappings.  If NO
    		 * entry is in the reserve map, it means a reservation exists.
    		 * If an entry exists in the reserve map, it means the
    		 * reservation has already been consumed.  As a result, the
    		 * return value of this routine is the opposite of the
    		 * value returned from reserve map manipulation routines above.
    		 */
    		if (ret)
    			return 0;
    		else
    			return 1;
    	}
    	else
    		return ret < 0 ? ret : 0;
    }
    
    static long vma_needs_reservation(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long addr)
    {
    	return __vma_reservation_common(h, vma, addr, VMA_NEEDS_RESV);
    }
    
    static long vma_commit_reservation(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long addr)
    {
    	return __vma_reservation_common(h, vma, addr, VMA_COMMIT_RESV);
    }
    
    static void vma_end_reservation(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long addr)
    {
    	(void)__vma_reservation_common(h, vma, addr, VMA_END_RESV);
    }
    
    static long vma_add_reservation(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long addr)
    {
    	return __vma_reservation_common(h, vma, addr, VMA_ADD_RESV);
    }
    
    /*
     * This routine is called to restore a reservation on error paths.  In the
     * specific error paths, a huge page was allocated (via alloc_huge_page)
     * and is about to be freed.  If a reservation for the page existed,
     * alloc_huge_page would have consumed the reservation and set PagePrivate
     * in the newly allocated page.  When the page is freed via free_huge_page,
     * the global reservation count will be incremented if PagePrivate is set.
     * However, free_huge_page can not adjust the reserve map.  Adjust the
     * reserve map here to be consistent with global reserve count adjustments
     * to be made by free_huge_page.
     */
    static void restore_reserve_on_error(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long address,
    			struct page *page)
    {
    	if (unlikely(PagePrivate(page))) {
    		long rc = vma_needs_reservation(h, vma, address);
    
    		if (unlikely(rc < 0)) {
    			/*
    			 * Rare out of memory condition in reserve map
    			 * manipulation.  Clear PagePrivate so that
    			 * global reserve count will not be incremented
    			 * by free_huge_page.  This will make it appear
    			 * as though the reservation for this page was
    			 * consumed.  This may prevent the task from
    			 * faulting in the page at a later time.  This
    			 * is better than inconsistent global huge page
    			 * accounting of reserve counts.
    			 */
    			ClearPagePrivate(page);
    		} else if (rc) {
    			rc = vma_add_reservation(h, vma, address);
    			if (unlikely(rc < 0))
    				/*
    				 * See above comment about rare out of
    				 * memory condition.
    				 */
    				ClearPagePrivate(page);
    		} else
    			vma_end_reservation(h, vma, address);
    	}
    }
    
    struct page *alloc_huge_page(struct vm_area_struct *vma,
    				    unsigned long addr, int avoid_reserve)
    {
    	struct hugepage_subpool *spool = subpool_vma(vma);
    	struct hstate *h = hstate_vma(vma);
    	struct page *page;
    	long map_chg, map_commit;
    	long gbl_chg;
    	int ret, idx;
    	struct hugetlb_cgroup *h_cg;
    	bool deferred_reserve;
    
    	idx = hstate_index(h);
    	/*
    	 * Examine the region/reserve map to determine if the process
    	 * has a reservation for the page to be allocated.  A return
    	 * code of zero indicates a reservation exists (no change).
    	 */
    	map_chg = gbl_chg = vma_needs_reservation(h, vma, addr);
    	if (map_chg < 0)
    		return ERR_PTR(-ENOMEM);
    
    	/*
    	 * Processes that did not create the mapping will have no
    	 * reserves as indicated by the region/reserve map. Check
    	 * that the allocation will not exceed the subpool limit.
    	 * Allocations for MAP_NORESERVE mappings also need to be
    	 * checked against any subpool limit.
    	 */
    	if (map_chg || avoid_reserve) {
    		gbl_chg = hugepage_subpool_get_pages(spool, 1);
    		if (gbl_chg < 0) {
    			vma_end_reservation(h, vma, addr);
    			return ERR_PTR(-ENOSPC);
    		}
    
    		/*
    		 * Even though there was no reservation in the region/reserve
    		 * map, there could be reservations associated with the
    		 * subpool that can be used.  This would be indicated if the
    		 * return value of hugepage_subpool_get_pages() is zero.
    		 * However, if avoid_reserve is specified we still avoid even
    		 * the subpool reservations.
    		 */
    		if (avoid_reserve)
    			gbl_chg = 1;
    	}
    
    	/* If this allocation is not consuming a reservation, charge it now.
    	 */
    	deferred_reserve = map_chg || avoid_reserve || !vma_resv_map(vma);
    	if (deferred_reserve) {
    		ret = hugetlb_cgroup_charge_cgroup_rsvd(
    			idx, pages_per_huge_page(h), &h_cg);
    		if (ret)
    			goto out_subpool_put;
    	}
    
    	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
    	if (ret)
    		goto out_uncharge_cgroup_reservation;
    
    	spin_lock(&hugetlb_lock);
    	/*
    	 * glb_chg is passed to indicate whether or not a page must be taken
    	 * from the global free pool (global change).  gbl_chg == 0 indicates
    	 * a reservation exists for the allocation.
    	 */
    	page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve, gbl_chg);
    	if (!page) {
    		spin_unlock(&hugetlb_lock);
    		page = alloc_buddy_huge_page_with_mpol(h, vma, addr);
    		if (!page)
    			goto out_uncharge_cgroup;
    		if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) {
    			SetPagePrivate(page);
    			h->resv_huge_pages--;
    		}
    		spin_lock(&hugetlb_lock);
    		list_add(&page->lru, &h->hugepage_activelist);
    		/* Fall through */
    	}
    	hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h), h_cg, page);
    	/* If allocation is not consuming a reservation, also store the
    	 * hugetlb_cgroup pointer on the page.
    	 */
    	if (deferred_reserve) {
    		hugetlb_cgroup_commit_charge_rsvd(idx, pages_per_huge_page(h),
    						  h_cg, page);
    	}
    
    	spin_unlock(&hugetlb_lock);
    
    	set_page_private(page, (unsigned long)spool);
    
    	map_commit = vma_commit_reservation(h, vma, addr);
    	if (unlikely(map_chg > map_commit)) {
    		/*
    		 * The page was added to the reservation map between
    		 * vma_needs_reservation and vma_commit_reservation.
    		 * This indicates a race with hugetlb_reserve_pages.
    		 * Adjust for the subpool count incremented above AND
    		 * in hugetlb_reserve_pages for the same page.  Also,
    		 * the reservation count added in hugetlb_reserve_pages
    		 * no longer applies.
    		 */
    		long rsv_adjust;
    
    		rsv_adjust = hugepage_subpool_put_pages(spool, 1);
    		hugetlb_acct_memory(h, -rsv_adjust);
    		if (deferred_reserve)
    			hugetlb_cgroup_uncharge_page_rsvd(hstate_index(h),
    					pages_per_huge_page(h), page);
    	}
    	return page;
    
    out_uncharge_cgroup:
    	hugetlb_cgroup_uncharge_cgroup(idx, pages_per_huge_page(h), h_cg);
    out_uncharge_cgroup_reservation:
    	if (deferred_reserve)
    		hugetlb_cgroup_uncharge_cgroup_rsvd(idx, pages_per_huge_page(h),
    						    h_cg);
    out_subpool_put:
    	if (map_chg || avoid_reserve)
    		hugepage_subpool_put_pages(spool, 1);
    	vma_end_reservation(h, vma, addr);
    	return ERR_PTR(-ENOSPC);
    }
    
    int alloc_bootmem_huge_page(struct hstate *h)
    	__attribute__ ((weak, alias("__alloc_bootmem_huge_page")));
    int __alloc_bootmem_huge_page(struct hstate *h)
    {
    	struct huge_bootmem_page *m;
    	int nr_nodes, node;
    
    	for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
    		void *addr;
    
    		addr = memblock_alloc_try_nid_raw(
    				huge_page_size(h), huge_page_size(h),
    				0, MEMBLOCK_ALLOC_ACCESSIBLE, node);
    		if (addr) {
    			/*
    			 * Use the beginning of the huge page to store the
    			 * huge_bootmem_page struct (until gather_bootmem
    			 * puts them into the mem_map).
    			 */
    			m = addr;
    			goto found;
    		}
    	}
    	return 0;
    
    found:
    	BUG_ON(!IS_ALIGNED(virt_to_phys(m), huge_page_size(h)));
    	/* Put them into a private list first because mem_map is not up yet */
    	INIT_LIST_HEAD(&m->list);
    	list_add(&m->list, &huge_boot_pages);
    	m->hstate = h;
    	return 1;
    }
    
    static void __init prep_compound_huge_page(struct page *page,
    		unsigned int order)
    {
    	if (unlikely(order > (MAX_ORDER - 1)))
    		prep_compound_gigantic_page(page, order);
    	else
    		prep_compound_page(page, order);
    }
    
    /* Put bootmem huge pages into the standard lists after mem_map is up */
    static void __init gather_bootmem_prealloc(void)
    {
    	struct huge_bootmem_page *m;
    
    	list_for_each_entry(m, &huge_boot_pages, list) {
    		struct page *page = virt_to_page(m);
    		struct hstate *h = m->hstate;
    
    		WARN_ON(page_count(page) != 1);
    		prep_compound_huge_page(page, h->order);
    		WARN_ON(PageReserved(page));
    		prep_new_huge_page(h, page, page_to_nid(page));
    		put_page(page); /* free it into the hugepage allocator */
    
    		/*
    		 * If we had gigantic hugepages allocated at boot time, we need
    		 * to restore the 'stolen' pages to totalram_pages in order to
    		 * fix confusing memory reports from free(1) and another
    		 * side-effects, like CommitLimit going negative.
    		 */
    		if (hstate_is_gigantic(h))
    			adjust_managed_page_count(page, 1 << h->order);
    		cond_resched();
    	}
    }
    
    static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
    {
    	unsigned long i;
    	nodemask_t *node_alloc_noretry;
    
    	if (!hstate_is_gigantic(h)) {
    		/*
    		 * Bit mask controlling how hard we retry per-node allocations.
    		 * Ignore errors as lower level routines can deal with
    		 * node_alloc_noretry == NULL.  If this kmalloc fails at boot
    		 * time, we are likely in bigger trouble.
    		 */
    		node_alloc_noretry = kmalloc(sizeof(*node_alloc_noretry),
    						GFP_KERNEL);
    	} else {
    		/* allocations done at boot time */
    		node_alloc_noretry = NULL;
    	}
    
    	/* bit mask controlling how hard we retry per-node allocations */
    	if (node_alloc_noretry)
    		nodes_clear(*node_alloc_noretry);
    
    	for (i = 0; i < h->max_huge_pages; ++i) {
    		if (hstate_is_gigantic(h)) {
    			if (hugetlb_cma_size) {
    				pr_warn_once("HugeTLB: hugetlb_cma is enabled, skip boot time allocation\n");
    				break;
    			}
    			if (!alloc_bootmem_huge_page(h))
    				break;
    		} else if (!alloc_pool_huge_page(h,
    					 &node_states[N_MEMORY],
    					 node_alloc_noretry))
    			break;
    		cond_resched();
    	}
    	if (i < h->max_huge_pages) {
    		char buf[32];
    
    		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
    		pr_warn("HugeTLB: allocating %lu of page size %s failed.  Only allocated %lu hugepages.\n",
    			h->max_huge_pages, buf, i);
    		h->max_huge_pages = i;
    	}
    
    	kfree(node_alloc_noretry);
    }
    
    static void __init hugetlb_init_hstates(void)
    {
    	struct hstate *h;
    
    	for_each_hstate(h) {
    		if (minimum_order > huge_page_order(h))
    			minimum_order = huge_page_order(h);
    
    		/* oversize hugepages were init'ed in early boot */
    		if (!hstate_is_gigantic(h))
    			hugetlb_hstate_alloc_pages(h);
    	}
    	VM_BUG_ON(minimum_order == UINT_MAX);
    }
    
    static void __init report_hugepages(void)
    {
    	struct hstate *h;
    
    	for_each_hstate(h) {
    		char buf[32];
    
    		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
    		pr_info("HugeTLB registered %s page size, pre-allocated %ld pages\n",
    			buf, h->free_huge_pages);
    	}
    }
    
    #ifdef CONFIG_HIGHMEM
    static void try_to_free_low(struct hstate *h, unsigned long count,
    						nodemask_t *nodes_allowed)
    {
    	int i;
    
    	if (hstate_is_gigantic(h))
    		return;
    
    	for_each_node_mask(i, *nodes_allowed) {
    		struct page *page, *next;
    		struct list_head *freel = &h->hugepage_freelists[i];
    		list_for_each_entry_safe(page, next, freel, lru) {
    			if (count >= h->nr_huge_pages)
    				return;
    			if (PageHighMem(page))
    				continue;
    			list_del(&page->lru);
    			update_and_free_page(h, page);
    			h->free_huge_pages--;
    			h->free_huge_pages_node[page_to_nid(page)]--;
    		}
    	}
    }
    #else
    static inline void try_to_free_low(struct hstate *h, unsigned long count,
    						nodemask_t *nodes_allowed)
    {
    }
    #endif
    
    /*
     * Increment or decrement surplus_huge_pages.  Keep node-specific counters
     * balanced by operating on them in a round-robin fashion.
     * Returns 1 if an adjustment was made.
     */
    static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
    				int delta)
    {
    	int nr_nodes, node;
    
    	VM_BUG_ON(delta != -1 && delta != 1);
    
    	if (delta < 0) {
    		for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
    			if (h->surplus_huge_pages_node[node])
    				goto found;
    		}
    	} else {
    		for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
    			if (h->surplus_huge_pages_node[node] <
    					h->nr_huge_pages_node[node])
    				goto found;
    		}
    	}
    	return 0;
    
    found:
    	h->surplus_huge_pages += delta;
    	h->surplus_huge_pages_node[node] += delta;
    	return 1;
    }
    
    #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
    static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
    			      nodemask_t *nodes_allowed)
    {
    	unsigned long min_count, ret;
    	NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
    
    	/*
    	 * Bit mask controlling how hard we retry per-node allocations.
    	 * If we can not allocate the bit mask, do not attempt to allocate
    	 * the requested huge pages.
    	 */
    	if (node_alloc_noretry)
    		nodes_clear(*node_alloc_noretry);
    	else
    		return -ENOMEM;
    
    	spin_lock(&hugetlb_lock);
    
    	/*
    	 * Check for a node specific request.
    	 * Changing node specific huge page count may require a corresponding
    	 * change to the global count.  In any case, the passed node mask
    	 * (nodes_allowed) will restrict alloc/free to the specified node.
    	 */
    	if (nid != NUMA_NO_NODE) {
    		unsigned long old_count = count;
    
    		count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
    		/*
    		 * User may have specified a large count value which caused the
    		 * above calculation to overflow.  In this case, they wanted
    		 * to allocate as many huge pages as possible.  Set count to
    		 * largest possible value to align with their intention.
    		 */
    		if (count < old_count)
    			count = ULONG_MAX;
    	}
    
    	/*
    	 * Gigantic pages runtime allocation depend on the capability for large
    	 * page range allocation.
    	 * If the system does not provide this feature, return an error when
    	 * the user tries to allocate gigantic pages but let the user free the
    	 * boottime allocated gigantic pages.
    	 */
    	if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
    		if (count > persistent_huge_pages(h)) {
    			spin_unlock(&hugetlb_lock);
    			NODEMASK_FREE(node_alloc_noretry);
    			return -EINVAL;
    		}
    		/* Fall through to decrease pool */
    	}
    
    	/*
    	 * Increase the pool size
    	 * First take pages out of surplus state.  Then make up the
    	 * remaining difference by allocating fresh huge pages.
    	 *
    	 * We might race with alloc_surplus_huge_page() here and be unable
    	 * to convert a surplus huge page to a normal huge page. That is
    	 * not critical, though, it just means the overall size of the
    	 * pool might be one hugepage larger than it needs to be, but
    	 * within all the constraints specified by the sysctls.
    	 */
    	while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
    		if (!adjust_pool_surplus(h, nodes_allowed, -1))
    			break;
    	}
    
    	while (count > persistent_huge_pages(h)) {
    		/*
    		 * If this allocation races such that we no longer need the
    		 * page, free_huge_page will handle it by freeing the page
    		 * and reducing the surplus.
    		 */
    		spin_unlock(&hugetlb_lock);
    
    		/* yield cpu to avoid soft lockup */
    		cond_resched();
    
    		ret = alloc_pool_huge_page(h, nodes_allowed,
    						node_alloc_noretry);
    		spin_lock(&hugetlb_lock);
    		if (!ret)
    			goto out;
    
    		/* Bail for signals. Probably ctrl-c from user */
    		if (signal_pending(current))
    			goto out;
    	}
    
    	/*
    	 * Decrease the pool size
    	 * First return free pages to the buddy allocator (being careful
    	 * to keep enough around to satisfy reservations).  Then place
    	 * pages into surplus state as needed so the pool will shrink
    	 * to the desired size as pages become free.
    	 *
    	 * By placing pages into the surplus state independent of the
    	 * overcommit value, we are allowing the surplus pool size to
    	 * exceed overcommit. There are few sane options here. Since
    	 * alloc_surplus_huge_page() is checking the global counter,
    	 * though, we'll note that we're not allowed to exceed surplus
    	 * and won't grow the pool anywhere else. Not until one of the
    	 * sysctls are changed, or the surplus pages go out of use.
    	 */
    	min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
    	min_count = max(count, min_count);
    	try_to_free_low(h, min_count, nodes_allowed);
    	while (min_count < persistent_huge_pages(h)) {
    		if (!free_pool_huge_page(h, nodes_allowed, 0))
    			break;
    		cond_resched_lock(&hugetlb_lock);
    	}
    	while (count < persistent_huge_pages(h)) {
    		if (!adjust_pool_surplus(h, nodes_allowed, 1))
    			break;
    	}
    out:
    	h->max_huge_pages = persistent_huge_pages(h);
    	spin_unlock(&hugetlb_lock);
    
    	NODEMASK_FREE(node_alloc_noretry);
    
    	return 0;
    }
    
    #define HSTATE_ATTR_RO(_name) \
    	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
    
    #define HSTATE_ATTR(_name) \
    	static struct kobj_attribute _name##_attr = \
    		__ATTR(_name, 0644, _name##_show, _name##_store)
    
    static struct kobject *hugepages_kobj;
    static struct kobject *hstate_kobjs[HUGE_MAX_HSTATE];
    
    static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp);
    
    static struct hstate *kobj_to_hstate(struct kobject *kobj, int *nidp)
    {
    	int i;
    
    	for (i = 0; i < HUGE_MAX_HSTATE; i++)
    		if (hstate_kobjs[i] == kobj) {
    			if (nidp)
    				*nidp = NUMA_NO_NODE;
    			return &hstates[i];
    		}
    
    	return kobj_to_node_hstate(kobj, nidp);
    }
    
    static ssize_t nr_hugepages_show_common(struct kobject *kobj,
    					struct kobj_attribute *attr, char *buf)
    {
    	struct hstate *h;
    	unsigned long nr_huge_pages;
    	int nid;
    
    	h = kobj_to_hstate(kobj, &nid);
    	if (nid == NUMA_NO_NODE)
    		nr_huge_pages = h->nr_huge_pages;
    	else
    		nr_huge_pages = h->nr_huge_pages_node[nid];
    
    	return sysfs_emit(buf, "%lu\n", nr_huge_pages);
    }
    
    static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
    					   struct hstate *h, int nid,
    					   unsigned long count, size_t len)
    {
    	int err;
    	nodemask_t nodes_allowed, *n_mask;
    
    	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
    		return -EINVAL;
    
    	if (nid == NUMA_NO_NODE) {
    		/*
    		 * global hstate attribute
    		 */
    		if (!(obey_mempolicy &&
    				init_nodemask_of_mempolicy(&nodes_allowed)))
    			n_mask = &node_states[N_MEMORY];
    		else
    			n_mask = &nodes_allowed;
    	} else {
    		/*
    		 * Node specific request.  count adjustment happens in
    		 * set_max_huge_pages() after acquiring hugetlb_lock.
    		 */
    		init_nodemask_of_node(&nodes_allowed, nid);
    		n_mask = &nodes_allowed;
    	}
    
    	err = set_max_huge_pages(h, count, nid, n_mask);
    
    	return err ? err : len;
    }
    
    static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
    					 struct kobject *kobj, const char *buf,
    					 size_t len)
    {
    	struct hstate *h;
    	unsigned long count;
    	int nid;
    	int err;
    
    	err = kstrtoul(buf, 10, &count);
    	if (err)
    		return err;
    
    	h = kobj_to_hstate(kobj, &nid);
    	return __nr_hugepages_store_common(obey_mempolicy, h, nid, count, len);
    }
    
    static ssize_t nr_hugepages_show(struct kobject *kobj,
    				       struct kobj_attribute *attr, char *buf)
    {
    	return nr_hugepages_show_common(kobj, attr, buf);
    }
    
    static ssize_t nr_hugepages_store(struct kobject *kobj,
    	       struct kobj_attribute *attr, const char *buf, size_t len)
    {
    	return nr_hugepages_store_common(false, kobj, buf, len);
    }
    HSTATE_ATTR(nr_hugepages);
    
    #ifdef CONFIG_NUMA
    
    /*
     * hstate attribute for optionally mempolicy-based constraint on persistent
     * huge page alloc/free.
     */
    static ssize_t nr_hugepages_mempolicy_show(struct kobject *kobj,
    					   struct kobj_attribute *attr,
    					   char *buf)
    {
    	return nr_hugepages_show_common(kobj, attr, buf);
    }
    
    static ssize_t nr_hugepages_mempolicy_store(struct kobject *kobj,
    	       struct kobj_attribute *attr, const char *buf, size_t len)
    {
    	return nr_hugepages_store_common(true, kobj, buf, len);
    }
    HSTATE_ATTR(nr_hugepages_mempolicy);
    #endif
    
    
    static ssize_t nr_overcommit_hugepages_show(struct kobject *kobj,
    					struct kobj_attribute *attr, char *buf)
    {
    	struct hstate *h = kobj_to_hstate(kobj, NULL);
    	return sysfs_emit(buf, "%lu\n", h->nr_overcommit_huge_pages);
    }
    
    static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
    		struct kobj_attribute *attr, const char *buf, size_t count)
    {
    	int err;
    	unsigned long input;
    	struct hstate *h = kobj_to_hstate(kobj, NULL);
    
    	if (hstate_is_gigantic(h))
    		return -EINVAL;
    
    	err = kstrtoul(buf, 10, &input);
    	if (err)
    		return err;
    
    	spin_lock(&hugetlb_lock);
    	h->nr_overcommit_huge_pages = input;
    	spin_unlock(&hugetlb_lock);
    
    	return count;
    }
    HSTATE_ATTR(nr_overcommit_hugepages);
    
    static ssize_t free_hugepages_show(struct kobject *kobj,
    					struct kobj_attribute *attr, char *buf)
    {
    	struct hstate *h;
    	unsigned long free_huge_pages;
    	int nid;
    
    	h = kobj_to_hstate(kobj, &nid);
    	if (nid == NUMA_NO_NODE)
    		free_huge_pages = h->free_huge_pages;
    	else
    		free_huge_pages = h->free_huge_pages_node[nid];
    
    	return sysfs_emit(buf, "%lu\n", free_huge_pages);
    }
    HSTATE_ATTR_RO(free_hugepages);
    
    static ssize_t resv_hugepages_show(struct kobject *kobj,
    					struct kobj_attribute *attr, char *buf)
    {
    	struct hstate *h = kobj_to_hstate(kobj, NULL);
    	return sysfs_emit(buf, "%lu\n", h->resv_huge_pages);
    }
    HSTATE_ATTR_RO(resv_hugepages);
    
    static ssize_t surplus_hugepages_show(struct kobject *kobj,
    					struct kobj_attribute *attr, char *buf)
    {
    	struct hstate *h;
    	unsigned long surplus_huge_pages;
    	int nid;
    
    	h = kobj_to_hstate(kobj, &nid);
    	if (nid == NUMA_NO_NODE)
    		surplus_huge_pages = h->surplus_huge_pages;
    	else
    		surplus_huge_pages = h->surplus_huge_pages_node[nid];
    
    	return sysfs_emit(buf, "%lu\n", surplus_huge_pages);
    }
    HSTATE_ATTR_RO(surplus_hugepages);
    
    static struct attribute *hstate_attrs[] = {
    	&nr_hugepages_attr.attr,
    	&nr_overcommit_hugepages_attr.attr,
    	&free_hugepages_attr.attr,
    	&resv_hugepages_attr.attr,
    	&surplus_hugepages_attr.attr,
    #ifdef CONFIG_NUMA
    	&nr_hugepages_mempolicy_attr.attr,
    #endif
    	NULL,
    };
    
    static const struct attribute_group hstate_attr_group = {
    	.attrs = hstate_attrs,
    };
    
    static int hugetlb_sysfs_add_hstate(struct hstate *h, struct kobject *parent,
    				    struct kobject **hstate_kobjs,
    				    const struct attribute_group *hstate_attr_group)
    {
    	int retval;
    	int hi = hstate_index(h);
    
    	hstate_kobjs[hi] = kobject_create_and_add(h->name, parent);
    	if (!hstate_kobjs[hi])
    		return -ENOMEM;
    
    	retval = sysfs_create_group(hstate_kobjs[hi], hstate_attr_group);
    	if (retval)
    		kobject_put(hstate_kobjs[hi]);
    
    	return retval;
    }
    
    static void __init hugetlb_sysfs_init(void)
    {
    	struct hstate *h;
    	int err;
    
    	hugepages_kobj = kobject_create_and_add("hugepages", mm_kobj);
    	if (!hugepages_kobj)
    		return;
    
    	for_each_hstate(h) {
    		err = hugetlb_sysfs_add_hstate(h, hugepages_kobj,
    					 hstate_kobjs, &hstate_attr_group);
    		if (err)
    			pr_err("HugeTLB: Unable to add hstate %s", h->name);
    	}
    }
    
    #ifdef CONFIG_NUMA
    
    /*
     * node_hstate/s - associate per node hstate attributes, via their kobjects,
     * with node devices in node_devices[] using a parallel array.  The array
     * index of a node device or _hstate == node id.
     * This is here to avoid any static dependency of the node device driver, in
     * the base kernel, on the hugetlb module.
     */
    struct node_hstate {
    	struct kobject		*hugepages_kobj;
    	struct kobject		*hstate_kobjs[HUGE_MAX_HSTATE];
    };
    static struct node_hstate node_hstates[MAX_NUMNODES];
    
    /*
     * A subset of global hstate attributes for node devices
     */
    static struct attribute *per_node_hstate_attrs[] = {
    	&nr_hugepages_attr.attr,
    	&free_hugepages_attr.attr,
    	&surplus_hugepages_attr.attr,
    	NULL,
    };
    
    static const struct attribute_group per_node_hstate_attr_group = {
    	.attrs = per_node_hstate_attrs,
    };
    
    /*
     * kobj_to_node_hstate - lookup global hstate for node device hstate attr kobj.
     * Returns node id via non-NULL nidp.
     */
    static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
    {
    	int nid;
    
    	for (nid = 0; nid < nr_node_ids; nid++) {
    		struct node_hstate *nhs = &node_hstates[nid];
    		int i;
    		for (i = 0; i < HUGE_MAX_HSTATE; i++)
    			if (nhs->hstate_kobjs[i] == kobj) {
    				if (nidp)
    					*nidp = nid;
    				return &hstates[i];
    			}
    	}
    
    	BUG();
    	return NULL;
    }
    
    /*
     * Unregister hstate attributes from a single node device.
     * No-op if no hstate attributes attached.
     */
    static void hugetlb_unregister_node(struct node *node)
    {
    	struct hstate *h;
    	struct node_hstate *nhs = &node_hstates[node->dev.id];
    
    	if (!nhs->hugepages_kobj)
    		return;		/* no hstate attributes */
    
    	for_each_hstate(h) {
    		int idx = hstate_index(h);
    		if (nhs->hstate_kobjs[idx]) {
    			kobject_put(nhs->hstate_kobjs[idx]);
    			nhs->hstate_kobjs[idx] = NULL;
    		}
    	}
    
    	kobject_put(nhs->hugepages_kobj);
    	nhs->hugepages_kobj = NULL;
    }
    
    
    /*
     * Register hstate attributes for a single node device.
     * No-op if attributes already registered.
     */
    static void hugetlb_register_node(struct node *node)
    {
    	struct hstate *h;
    	struct node_hstate *nhs = &node_hstates[node->dev.id];
    	int err;
    
    	if (nhs->hugepages_kobj)
    		return;		/* already allocated */
    
    	nhs->hugepages_kobj = kobject_create_and_add("hugepages",
    							&node->dev.kobj);
    	if (!nhs->hugepages_kobj)
    		return;
    
    	for_each_hstate(h) {
    		err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
    						nhs->hstate_kobjs,
    						&per_node_hstate_attr_group);
    		if (err) {
    			pr_err("HugeTLB: Unable to add hstate %s for node %d\n",
    				h->name, node->dev.id);
    			hugetlb_unregister_node(node);
    			break;
    		}
    	}
    }
    
    /*
     * hugetlb init time:  register hstate attributes for all registered node
     * devices of nodes that have memory.  All on-line nodes should have
     * registered their associated device by this time.
     */
    static void __init hugetlb_register_all_nodes(void)
    {
    	int nid;
    
    	for_each_node_state(nid, N_MEMORY) {
    		struct node *node = node_devices[nid];
    		if (node->dev.id == nid)
    			hugetlb_register_node(node);
    	}
    
    	/*
    	 * Let the node device driver know we're here so it can
    	 * [un]register hstate attributes on node hotplug.
    	 */
    	register_hugetlbfs_with_node(hugetlb_register_node,
    				     hugetlb_unregister_node);
    }
    #else	/* !CONFIG_NUMA */
    
    static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
    {
    	BUG();
    	if (nidp)
    		*nidp = -1;
    	return NULL;
    }
    
    static void hugetlb_register_all_nodes(void) { }
    
    #endif
    
    static int __init hugetlb_init(void)
    {
    	int i;
    
    	if (!hugepages_supported()) {
    		if (hugetlb_max_hstate || default_hstate_max_huge_pages)
    			pr_warn("HugeTLB: huge pages not supported, ignoring associated command-line parameters\n");
    		return 0;
    	}
    
    	/*
    	 * Make sure HPAGE_SIZE (HUGETLB_PAGE_ORDER) hstate exists.  Some
    	 * architectures depend on setup being done here.
    	 */
    	hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
    	if (!parsed_default_hugepagesz) {
    		/*
    		 * If we did not parse a default huge page size, set
    		 * default_hstate_idx to HPAGE_SIZE hstate. And, if the
    		 * number of huge pages for this default size was implicitly
    		 * specified, set that here as well.
    		 * Note that the implicit setting will overwrite an explicit
    		 * setting.  A warning will be printed in this case.
    		 */
    		default_hstate_idx = hstate_index(size_to_hstate(HPAGE_SIZE));
    		if (default_hstate_max_huge_pages) {
    			if (default_hstate.max_huge_pages) {
    				char buf[32];
    
    				string_get_size(huge_page_size(&default_hstate),
    					1, STRING_UNITS_2, buf, 32);
    				pr_warn("HugeTLB: Ignoring hugepages=%lu associated with %s page size\n",
    					default_hstate.max_huge_pages, buf);
    				pr_warn("HugeTLB: Using hugepages=%lu for number of default huge pages\n",
    					default_hstate_max_huge_pages);
    			}
    			default_hstate.max_huge_pages =
    				default_hstate_max_huge_pages;
    		}
    	}
    
    	hugetlb_cma_check();
    	hugetlb_init_hstates();
    	gather_bootmem_prealloc();
    	report_hugepages();
    
    	hugetlb_sysfs_init();
    	hugetlb_register_all_nodes();
    	hugetlb_cgroup_file_init();
    
    #ifdef CONFIG_SMP
    	num_fault_mutexes = roundup_pow_of_two(8 * num_possible_cpus());
    #else
    	num_fault_mutexes = 1;
    #endif
    	hugetlb_fault_mutex_table =
    		kmalloc_array(num_fault_mutexes, sizeof(struct mutex),
    			      GFP_KERNEL);
    	BUG_ON(!hugetlb_fault_mutex_table);
    
    	for (i = 0; i < num_fault_mutexes; i++)
    		mutex_init(&hugetlb_fault_mutex_table[i]);
    	return 0;
    }
    subsys_initcall(hugetlb_init);
    
    /* Overwritten by architectures with more huge page sizes */
    bool __init __attribute((weak)) arch_hugetlb_valid_size(unsigned long size)
    {
    	return size == HPAGE_SIZE;
    }
    
    void __init hugetlb_add_hstate(unsigned int order)
    {
    	struct hstate *h;
    	unsigned long i;
    
    	if (size_to_hstate(PAGE_SIZE << order)) {
    		return;
    	}
    	BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
    	BUG_ON(order == 0);
    	h = &hstates[hugetlb_max_hstate++];
    	h->order = order;
    	h->mask = ~((1ULL << (order + PAGE_SHIFT)) - 1);
    	for (i = 0; i < MAX_NUMNODES; ++i)
    		INIT_LIST_HEAD(&h->hugepage_freelists[i]);
    	INIT_LIST_HEAD(&h->hugepage_activelist);
    	h->next_nid_to_alloc = first_memory_node;
    	h->next_nid_to_free = first_memory_node;
    	snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
    					huge_page_size(h)/1024);
    
    	parsed_hstate = h;
    }
    
    /*
     * hugepages command line processing
     * hugepages normally follows a valid hugepagsz or default_hugepagsz
     * specification.  If not, ignore the hugepages value.  hugepages can also
     * be the first huge page command line  option in which case it implicitly
     * specifies the number of huge pages for the default size.
     */
    static int __init hugepages_setup(char *s)
    {
    	unsigned long *mhp;
    	static unsigned long *last_mhp;
    
    	if (!parsed_valid_hugepagesz) {
    		pr_warn("HugeTLB: hugepages=%s does not follow a valid hugepagesz, ignoring\n", s);
    		parsed_valid_hugepagesz = true;
    		return 0;
    	}
    
    	/*
    	 * !hugetlb_max_hstate means we haven't parsed a hugepagesz= parameter
    	 * yet, so this hugepages= parameter goes to the "default hstate".
    	 * Otherwise, it goes with the previously parsed hugepagesz or
    	 * default_hugepagesz.
    	 */
    	else if (!hugetlb_max_hstate)
    		mhp = &default_hstate_max_huge_pages;
    	else
    		mhp = &parsed_hstate->max_huge_pages;
    
    	if (mhp == last_mhp) {
    		pr_warn("HugeTLB: hugepages= specified twice without interleaving hugepagesz=, ignoring hugepages=%s\n", s);
    		return 0;
    	}
    
    	if (sscanf(s, "%lu", mhp) <= 0)
    		*mhp = 0;
    
    	/*
    	 * Global state is always initialized later in hugetlb_init.
    	 * But we need to allocate >= MAX_ORDER hstates here early to still
    	 * use the bootmem allocator.
    	 */
    	if (hugetlb_max_hstate && parsed_hstate->order >= MAX_ORDER)
    		hugetlb_hstate_alloc_pages(parsed_hstate);
    
    	last_mhp = mhp;
    
    	return 1;
    }
    __setup("hugepages=", hugepages_setup);
    
    /*
     * hugepagesz command line processing
     * A specific huge page size can only be specified once with hugepagesz.
     * hugepagesz is followed by hugepages on the command line.  The global
     * variable 'parsed_valid_hugepagesz' is used to determine if prior
     * hugepagesz argument was valid.
     */
    static int __init hugepagesz_setup(char *s)
    {
    	unsigned long size;
    	struct hstate *h;
    
    	parsed_valid_hugepagesz = false;
    	size = (unsigned long)memparse(s, NULL);
    
    	if (!arch_hugetlb_valid_size(size)) {
    		pr_err("HugeTLB: unsupported hugepagesz=%s\n", s);
    		return 0;
    	}
    
    	h = size_to_hstate(size);
    	if (h) {
    		/*
    		 * hstate for this size already exists.  This is normally
    		 * an error, but is allowed if the existing hstate is the
    		 * default hstate.  More specifically, it is only allowed if
    		 * the number of huge pages for the default hstate was not
    		 * previously specified.
    		 */
    		if (!parsed_default_hugepagesz ||  h != &default_hstate ||
    		    default_hstate.max_huge_pages) {
    			pr_warn("HugeTLB: hugepagesz=%s specified twice, ignoring\n", s);
    			return 0;
    		}
    
    		/*
    		 * No need to call hugetlb_add_hstate() as hstate already
    		 * exists.  But, do set parsed_hstate so that a following
    		 * hugepages= parameter will be applied to this hstate.
    		 */
    		parsed_hstate = h;
    		parsed_valid_hugepagesz = true;
    		return 1;
    	}
    
    	hugetlb_add_hstate(ilog2(size) - PAGE_SHIFT);
    	parsed_valid_hugepagesz = true;
    	return 1;
    }
    __setup("hugepagesz=", hugepagesz_setup);
    
    /*
     * default_hugepagesz command line input
     * Only one instance of default_hugepagesz allowed on command line.
     */
    static int __init default_hugepagesz_setup(char *s)
    {
    	unsigned long size;
    
    	parsed_valid_hugepagesz = false;
    	if (parsed_default_hugepagesz) {
    		pr_err("HugeTLB: default_hugepagesz previously specified, ignoring %s\n", s);
    		return 0;
    	}
    
    	size = (unsigned long)memparse(s, NULL);
    
    	if (!arch_hugetlb_valid_size(size)) {
    		pr_err("HugeTLB: unsupported default_hugepagesz=%s\n", s);
    		return 0;
    	}
    
    	hugetlb_add_hstate(ilog2(size) - PAGE_SHIFT);
    	parsed_valid_hugepagesz = true;
    	parsed_default_hugepagesz = true;
    	default_hstate_idx = hstate_index(size_to_hstate(size));
    
    	/*
    	 * The number of default huge pages (for this size) could have been
    	 * specified as the first hugetlb parameter: hugepages=X.  If so,
    	 * then default_hstate_max_huge_pages is set.  If the default huge
    	 * page size is gigantic (>= MAX_ORDER), then the pages must be
    	 * allocated here from bootmem allocator.
    	 */
    	if (default_hstate_max_huge_pages) {
    		default_hstate.max_huge_pages = default_hstate_max_huge_pages;
    		if (hstate_is_gigantic(&default_hstate))
    			hugetlb_hstate_alloc_pages(&default_hstate);
    		default_hstate_max_huge_pages = 0;
    	}
    
    	return 1;
    }
    __setup("default_hugepagesz=", default_hugepagesz_setup);
    
    static unsigned int allowed_mems_nr(struct hstate *h)
    {
    	int node;
    	unsigned int nr = 0;
    	nodemask_t *mpol_allowed;
    	unsigned int *array = h->free_huge_pages_node;
    	gfp_t gfp_mask = htlb_alloc_mask(h);
    
    	mpol_allowed = policy_nodemask_current(gfp_mask);
    
    	for_each_node_mask(node, cpuset_current_mems_allowed) {
    		if (!mpol_allowed ||
    		    (mpol_allowed && node_isset(node, *mpol_allowed)))
    			nr += array[node];
    	}
    
    	return nr;
    }
    
    #ifdef CONFIG_SYSCTL
    static int proc_hugetlb_doulongvec_minmax(struct ctl_table *table, int write,
    					  void *buffer, size_t *length,
    					  loff_t *ppos, unsigned long *out)
    {
    	struct ctl_table dup_table;
    
    	/*
    	 * In order to avoid races with __do_proc_doulongvec_minmax(), we
    	 * can duplicate the @table and alter the duplicate of it.
    	 */
    	dup_table = *table;
    	dup_table.data = out;
    
    	return proc_doulongvec_minmax(&dup_table, write, buffer, length, ppos);
    }
    
    static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
    			 struct ctl_table *table, int write,
    			 void *buffer, size_t *length, loff_t *ppos)
    {
    	struct hstate *h = &default_hstate;
    	unsigned long tmp = h->max_huge_pages;
    	int ret;
    
    	if (!hugepages_supported())
    		return -EOPNOTSUPP;
    
    	ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos,
    					     &tmp);
    	if (ret)
    		goto out;
    
    	if (write)
    		ret = __nr_hugepages_store_common(obey_mempolicy, h,
    						  NUMA_NO_NODE, tmp, *length);
    out:
    	return ret;
    }
    
    int hugetlb_sysctl_handler(struct ctl_table *table, int write,
    			  void *buffer, size_t *length, loff_t *ppos)
    {
    
    	return hugetlb_sysctl_handler_common(false, table, write,
    							buffer, length, ppos);
    }
    
    #ifdef CONFIG_NUMA
    int hugetlb_mempolicy_sysctl_handler(struct ctl_table *table, int write,
    			  void *buffer, size_t *length, loff_t *ppos)
    {
    	return hugetlb_sysctl_handler_common(true, table, write,
    							buffer, length, ppos);
    }
    #endif /* CONFIG_NUMA */
    
    int hugetlb_overcommit_handler(struct ctl_table *table, int write,
    		void *buffer, size_t *length, loff_t *ppos)
    {
    	struct hstate *h = &default_hstate;
    	unsigned long tmp;
    	int ret;
    
    	if (!hugepages_supported())
    		return -EOPNOTSUPP;
    
    	tmp = h->nr_overcommit_huge_pages;
    
    	if (write && hstate_is_gigantic(h))
    		return -EINVAL;
    
    	ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos,
    					     &tmp);
    	if (ret)
    		goto out;
    
    	if (write) {
    		spin_lock(&hugetlb_lock);
    		h->nr_overcommit_huge_pages = tmp;
    		spin_unlock(&hugetlb_lock);
    	}
    out:
    	return ret;
    }
    
    #endif /* CONFIG_SYSCTL */
    
    void hugetlb_report_meminfo(struct seq_file *m)
    {
    	struct hstate *h;
    	unsigned long total = 0;
    
    	if (!hugepages_supported())
    		return;
    
    	for_each_hstate(h) {
    		unsigned long count = h->nr_huge_pages;
    
    		total += (PAGE_SIZE << huge_page_order(h)) * count;
    
    		if (h == &default_hstate)
    			seq_printf(m,
    				   "HugePages_Total:   %5lu\n"
    				   "HugePages_Free:    %5lu\n"
    				   "HugePages_Rsvd:    %5lu\n"
    				   "HugePages_Surp:    %5lu\n"
    				   "Hugepagesize:   %8lu kB\n",
    				   count,
    				   h->free_huge_pages,
    				   h->resv_huge_pages,
    				   h->surplus_huge_pages,
    				   (PAGE_SIZE << huge_page_order(h)) / 1024);
    	}
    
    	seq_printf(m, "Hugetlb:        %8lu kB\n", total / 1024);
    }
    
    int hugetlb_report_node_meminfo(char *buf, int len, int nid)
    {
    	struct hstate *h = &default_hstate;
    
    	if (!hugepages_supported())
    		return 0;
    
    	return sysfs_emit_at(buf, len,
    			     "Node %d HugePages_Total: %5u\n"
    			     "Node %d HugePages_Free:  %5u\n"
    			     "Node %d HugePages_Surp:  %5u\n",
    			     nid, h->nr_huge_pages_node[nid],
    			     nid, h->free_huge_pages_node[nid],
    			     nid, h->surplus_huge_pages_node[nid]);
    }
    
    void hugetlb_show_meminfo(void)
    {
    	struct hstate *h;
    	int nid;
    
    	if (!hugepages_supported())
    		return;
    
    	for_each_node_state(nid, N_MEMORY)
    		for_each_hstate(h)
    			pr_info("Node %d hugepages_total=%u hugepages_free=%u hugepages_surp=%u hugepages_size=%lukB\n",
    				nid,
    				h->nr_huge_pages_node[nid],
    				h->free_huge_pages_node[nid],
    				h->surplus_huge_pages_node[nid],
    				1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
    }
    
    void hugetlb_report_usage(struct seq_file *m, struct mm_struct *mm)
    {
    	seq_printf(m, "HugetlbPages:\t%8lu kB\n",
    		   atomic_long_read(&mm->hugetlb_usage) << (PAGE_SHIFT - 10));
    }
    
    /* Return the number pages of memory we physically have, in PAGE_SIZE units. */
    unsigned long hugetlb_total_pages(void)
    {
    	struct hstate *h;
    	unsigned long nr_total_pages = 0;
    
    	for_each_hstate(h)
    		nr_total_pages += h->nr_huge_pages * pages_per_huge_page(h);
    	return nr_total_pages;
    }
    
    static int hugetlb_acct_memory(struct hstate *h, long delta)
    {
    	int ret = -ENOMEM;
    
    	spin_lock(&hugetlb_lock);
    	/*
    	 * When cpuset is configured, it breaks the strict hugetlb page
    	 * reservation as the accounting is done on a global variable. Such
    	 * reservation is completely rubbish in the presence of cpuset because
    	 * the reservation is not checked against page availability for the
    	 * current cpuset. Application can still potentially OOM'ed by kernel
    	 * with lack of free htlb page in cpuset that the task is in.
    	 * Attempt to enforce strict accounting with cpuset is almost
    	 * impossible (or too ugly) because cpuset is too fluid that
    	 * task or memory node can be dynamically moved between cpusets.
    	 *
    	 * The change of semantics for shared hugetlb mapping with cpuset is
    	 * undesirable. However, in order to preserve some of the semantics,
    	 * we fall back to check against current free page availability as
    	 * a best attempt and hopefully to minimize the impact of changing
    	 * semantics that cpuset has.
    	 *
    	 * Apart from cpuset, we also have memory policy mechanism that
    	 * also determines from which node the kernel will allocate memory
    	 * in a NUMA system. So similar to cpuset, we also should consider
    	 * the memory policy of the current task. Similar to the description
    	 * above.
    	 */
    	if (delta > 0) {
    		if (gather_surplus_pages(h, delta) < 0)
    			goto out;
    
    		if (delta > allowed_mems_nr(h)) {
    			return_unused_surplus_pages(h, delta);
    			goto out;
    		}
    	}
    
    	ret = 0;
    	if (delta < 0)
    		return_unused_surplus_pages(h, (unsigned long) -delta);
    
    out:
    	spin_unlock(&hugetlb_lock);
    	return ret;
    }
    
    static void hugetlb_vm_op_open(struct vm_area_struct *vma)
    {
    	struct resv_map *resv = vma_resv_map(vma);
    
    	/*
    	 * This new VMA should share its siblings reservation map if present.
    	 * The VMA will only ever have a valid reservation map pointer where
    	 * it is being copied for another still existing VMA.  As that VMA
    	 * has a reference to the reservation map it cannot disappear until
    	 * after this open call completes.  It is therefore safe to take a
    	 * new reference here without additional locking.
    	 */
    	if (resv && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
    		kref_get(&resv->refs);
    }
    
    static void hugetlb_vm_op_close(struct vm_area_struct *vma)
    {
    	struct hstate *h = hstate_vma(vma);
    	struct resv_map *resv = vma_resv_map(vma);
    	struct hugepage_subpool *spool = subpool_vma(vma);
    	unsigned long reserve, start, end;
    	long gbl_reserve;
    
    	if (!resv || !is_vma_resv_set(vma, HPAGE_RESV_OWNER))
    		return;
    
    	start = vma_hugecache_offset(h, vma, vma->vm_start);
    	end = vma_hugecache_offset(h, vma, vma->vm_end);
    
    	reserve = (end - start) - region_count(resv, start, end);
    	hugetlb_cgroup_uncharge_counter(resv, start, end);
    	if (reserve) {
    		/*
    		 * Decrement reserve counts.  The global reserve count may be
    		 * adjusted if the subpool has a minimum size.
    		 */
    		gbl_reserve = hugepage_subpool_put_pages(spool, reserve);
    		hugetlb_acct_memory(h, -gbl_reserve);
    	}
    
    	kref_put(&resv->refs, resv_map_release);
    }
    
    static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
    {
    	if (addr & ~(huge_page_mask(hstate_vma(vma))))
    		return -EINVAL;
    	return 0;
    }
    
    static unsigned long hugetlb_vm_op_pagesize(struct vm_area_struct *vma)
    {
    	struct hstate *hstate = hstate_vma(vma);
    
    	return 1UL << huge_page_shift(hstate);
    }
    
    /*
     * We cannot handle pagefaults against hugetlb pages at all.  They cause
     * handle_mm_fault() to try to instantiate regular-sized pages in the
     * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
     * this far.
     */
    static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf)
    {
    	BUG();
    	return 0;
    }
    
    /*
     * When a new function is introduced to vm_operations_struct and added
     * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops.
     * This is because under System V memory model, mappings created via
     * shmget/shmat with "huge page" specified are backed by hugetlbfs files,
     * their original vm_ops are overwritten with shm_vm_ops.
     */
    const struct vm_operations_struct hugetlb_vm_ops = {
    	.fault = hugetlb_vm_op_fault,
    	.open = hugetlb_vm_op_open,
    	.close = hugetlb_vm_op_close,
    	.may_split = hugetlb_vm_op_split,
    	.pagesize = hugetlb_vm_op_pagesize,
    };
    
    static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
    				int writable)
    {
    	pte_t entry;
    
    	if (writable) {
    		entry = huge_pte_mkwrite(huge_pte_mkdirty(mk_huge_pte(page,
    					 vma->vm_page_prot)));
    	} else {
    		entry = huge_pte_wrprotect(mk_huge_pte(page,
    					   vma->vm_page_prot));
    	}
    	entry = pte_mkyoung(entry);
    	entry = pte_mkhuge(entry);
    	entry = arch_make_huge_pte(entry, vma, page, writable);
    
    	return entry;
    }
    
    static void set_huge_ptep_writable(struct vm_area_struct *vma,
    				   unsigned long address, pte_t *ptep)
    {
    	pte_t entry;
    
    	entry = huge_pte_mkwrite(huge_pte_mkdirty(huge_ptep_get(ptep)));
    	if (huge_ptep_set_access_flags(vma, address, ptep, entry, 1))
    		update_mmu_cache(vma, address, ptep);
    }
    
    bool is_hugetlb_entry_migration(pte_t pte)
    {
    	swp_entry_t swp;
    
    	if (huge_pte_none(pte) || pte_present(pte))
    		return false;
    	swp = pte_to_swp_entry(pte);
    	if (is_migration_entry(swp))
    		return true;
    	else
    		return false;
    }
    
    static bool is_hugetlb_entry_hwpoisoned(pte_t pte)
    {
    	swp_entry_t swp;
    
    	if (huge_pte_none(pte) || pte_present(pte))
    		return false;
    	swp = pte_to_swp_entry(pte);
    	if (is_hwpoison_entry(swp))
    		return true;
    	else
    		return false;
    }
    
    int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
    			    struct vm_area_struct *vma)
    {
    	pte_t *src_pte, *dst_pte, entry, dst_entry;
    	struct page *ptepage;
    	unsigned long addr;
    	int cow;
    	struct hstate *h = hstate_vma(vma);
    	unsigned long sz = huge_page_size(h);
    	struct address_space *mapping = vma->vm_file->f_mapping;
    	struct mmu_notifier_range range;
    	int ret = 0;
    
    	cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
    
    	if (cow) {
    		mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, src,
    					vma->vm_start,
    					vma->vm_end);
    		mmu_notifier_invalidate_range_start(&range);
    	} else {
    		/*
    		 * For shared mappings i_mmap_rwsem must be held to call
    		 * huge_pte_alloc, otherwise the returned ptep could go
    		 * away if part of a shared pmd and another thread calls
    		 * huge_pmd_unshare.
    		 */
    		i_mmap_lock_read(mapping);
    	}
    
    	for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
    		spinlock_t *src_ptl, *dst_ptl;
    		src_pte = huge_pte_offset(src, addr, sz);
    		if (!src_pte)
    			continue;
    		dst_pte = huge_pte_alloc(dst, addr, sz);
    		if (!dst_pte) {
    			ret = -ENOMEM;
    			break;
    		}
    
    		/*
    		 * If the pagetables are shared don't copy or take references.
    		 * dst_pte == src_pte is the common case of src/dest sharing.
    		 *
    		 * However, src could have 'unshared' and dst shares with
    		 * another vma.  If dst_pte !none, this implies sharing.
    		 * Check here before taking page table lock, and once again
    		 * after taking the lock below.
    		 */
    		dst_entry = huge_ptep_get(dst_pte);
    		if ((dst_pte == src_pte) || !huge_pte_none(dst_entry))
    			continue;
    
    		dst_ptl = huge_pte_lock(h, dst, dst_pte);
    		src_ptl = huge_pte_lockptr(h, src, src_pte);
    		spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
    		entry = huge_ptep_get(src_pte);
    		dst_entry = huge_ptep_get(dst_pte);
    		if (huge_pte_none(entry) || !huge_pte_none(dst_entry)) {
    			/*
    			 * Skip if src entry none.  Also, skip in the
    			 * unlikely case dst entry !none as this implies
    			 * sharing with another vma.
    			 */
    			;
    		} else if (unlikely(is_hugetlb_entry_migration(entry) ||
    				    is_hugetlb_entry_hwpoisoned(entry))) {
    			swp_entry_t swp_entry = pte_to_swp_entry(entry);
    
    			if (is_write_migration_entry(swp_entry) && cow) {
    				/*
    				 * COW mappings require pages in both
    				 * parent and child to be set to read.
    				 */
    				make_migration_entry_read(&swp_entry);
    				entry = swp_entry_to_pte(swp_entry);
    				set_huge_swap_pte_at(src, addr, src_pte,
    						     entry, sz);
    			}
    			set_huge_swap_pte_at(dst, addr, dst_pte, entry, sz);
    		} else {
    			if (cow) {
    				/*
    				 * No need to notify as we are downgrading page
    				 * table protection not changing it to point
    				 * to a new page.
    				 *
    				 * See Documentation/vm/mmu_notifier.rst
    				 */
    				huge_ptep_set_wrprotect(src, addr, src_pte);
    			}
    			entry = huge_ptep_get(src_pte);
    			ptepage = pte_page(entry);
    			get_page(ptepage);
    			page_dup_rmap(ptepage, true);
    			set_huge_pte_at(dst, addr, dst_pte, entry);
    			hugetlb_count_add(pages_per_huge_page(h), dst);
    		}
    		spin_unlock(src_ptl);
    		spin_unlock(dst_ptl);
    	}
    
    	if (cow)
    		mmu_notifier_invalidate_range_end(&range);
    	else
    		i_mmap_unlock_read(mapping);
    
    	return ret;
    }
    
    void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
    			    unsigned long start, unsigned long end,
    			    struct page *ref_page)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	unsigned long address;
    	pte_t *ptep;
    	pte_t pte;
    	spinlock_t *ptl;
    	struct page *page;
    	struct hstate *h = hstate_vma(vma);
    	unsigned long sz = huge_page_size(h);
    	struct mmu_notifier_range range;
    
    	WARN_ON(!is_vm_hugetlb_page(vma));
    	BUG_ON(start & ~huge_page_mask(h));
    	BUG_ON(end & ~huge_page_mask(h));
    
    	/*
    	 * This is a hugetlb vma, all the pte entries should point
    	 * to huge page.
    	 */
    	tlb_change_page_size(tlb, sz);
    	tlb_start_vma(tlb, vma);
    
    	/*
    	 * If sharing possible, alert mmu notifiers of worst case.
    	 */
    	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, mm, start,
    				end);
    	adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
    	mmu_notifier_invalidate_range_start(&range);
    	address = start;
    	for (; address < end; address += sz) {
    		ptep = huge_pte_offset(mm, address, sz);
    		if (!ptep)
    			continue;
    
    		ptl = huge_pte_lock(h, mm, ptep);
    		if (huge_pmd_unshare(mm, vma, &address, ptep)) {
    			spin_unlock(ptl);
    			/*
    			 * We just unmapped a page of PMDs by clearing a PUD.
    			 * The caller's TLB flush range should cover this area.
    			 */
    			continue;
    		}
    
    		pte = huge_ptep_get(ptep);
    		if (huge_pte_none(pte)) {
    			spin_unlock(ptl);
    			continue;
    		}
    
    		/*
    		 * Migrating hugepage or HWPoisoned hugepage is already
    		 * unmapped and its refcount is dropped, so just clear pte here.
    		 */
    		if (unlikely(!pte_present(pte))) {
    			huge_pte_clear(mm, address, ptep, sz);
    			spin_unlock(ptl);
    			continue;
    		}
    
    		page = pte_page(pte);
    		/*
    		 * If a reference page is supplied, it is because a specific
    		 * page is being unmapped, not a range. Ensure the page we
    		 * are about to unmap is the actual page of interest.
    		 */
    		if (ref_page) {
    			if (page != ref_page) {
    				spin_unlock(ptl);
    				continue;
    			}
    			/*
    			 * Mark the VMA as having unmapped its page so that
    			 * future faults in this VMA will fail rather than
    			 * looking like data was lost
    			 */
    			set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
    		}
    
    		pte = huge_ptep_get_and_clear(mm, address, ptep);
    		tlb_remove_huge_tlb_entry(h, tlb, ptep, address);
    		if (huge_pte_dirty(pte))
    			set_page_dirty(page);
    
    		hugetlb_count_sub(pages_per_huge_page(h), mm);
    		page_remove_rmap(page, true);
    
    		spin_unlock(ptl);
    		tlb_remove_page_size(tlb, page, huge_page_size(h));
    		/*
    		 * Bail out after unmapping reference page if supplied
    		 */
    		if (ref_page)
    			break;
    	}
    	mmu_notifier_invalidate_range_end(&range);
    	tlb_end_vma(tlb, vma);
    }
    
    void __unmap_hugepage_range_final(struct mmu_gather *tlb,
    			  struct vm_area_struct *vma, unsigned long start,
    			  unsigned long end, struct page *ref_page)
    {
    	__unmap_hugepage_range(tlb, vma, start, end, ref_page);
    
    	/*
    	 * Clear this flag so that x86's huge_pmd_share page_table_shareable
    	 * test will fail on a vma being torn down, and not grab a page table
    	 * on its way out.  We're lucky that the flag has such an appropriate
    	 * name, and can in fact be safely cleared here. We could clear it
    	 * before the __unmap_hugepage_range above, but all that's necessary
    	 * is to clear it before releasing the i_mmap_rwsem. This works
    	 * because in the context this is called, the VMA is about to be
    	 * destroyed and the i_mmap_rwsem is held.
    	 */
    	vma->vm_flags &= ~VM_MAYSHARE;
    }
    
    void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
    			  unsigned long end, struct page *ref_page)
    {
    	struct mm_struct *mm;
    	struct mmu_gather tlb;
    	unsigned long tlb_start = start;
    	unsigned long tlb_end = end;
    
    	/*
    	 * If shared PMDs were possibly used within this vma range, adjust
    	 * start/end for worst case tlb flushing.
    	 * Note that we can not be sure if PMDs are shared until we try to
    	 * unmap pages.  However, we want to make sure TLB flushing covers
    	 * the largest possible range.
    	 */
    	adjust_range_if_pmd_sharing_possible(vma, &tlb_start, &tlb_end);
    
    	mm = vma->vm_mm;
    
    	tlb_gather_mmu(&tlb, mm, tlb_start, tlb_end);
    	__unmap_hugepage_range(&tlb, vma, start, end, ref_page);
    	tlb_finish_mmu(&tlb, tlb_start, tlb_end);
    }
    
    /*
     * This is called when the original mapper is failing to COW a MAP_PRIVATE
     * mappping it owns the reserve page for. The intention is to unmap the page
     * from other VMAs and let the children be SIGKILLed if they are faulting the
     * same region.
     */
    static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
    			      struct page *page, unsigned long address)
    {
    	struct hstate *h = hstate_vma(vma);
    	struct vm_area_struct *iter_vma;
    	struct address_space *mapping;
    	pgoff_t pgoff;
    
    	/*
    	 * vm_pgoff is in PAGE_SIZE units, hence the different calculation
    	 * from page cache lookup which is in HPAGE_SIZE units.
    	 */
    	address = address & huge_page_mask(h);
    	pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
    			vma->vm_pgoff;
    	mapping = vma->vm_file->f_mapping;
    
    	/*
    	 * Take the mapping lock for the duration of the table walk. As
    	 * this mapping should be shared between all the VMAs,
    	 * __unmap_hugepage_range() is called as the lock is already held
    	 */
    	i_mmap_lock_write(mapping);
    	vma_interval_tree_foreach(iter_vma, &mapping->i_mmap, pgoff, pgoff) {
    		/* Do not unmap the current VMA */
    		if (iter_vma == vma)
    			continue;
    
    		/*
    		 * Shared VMAs have their own reserves and do not affect
    		 * MAP_PRIVATE accounting but it is possible that a shared
    		 * VMA is using the same page so check and skip such VMAs.
    		 */
    		if (iter_vma->vm_flags & VM_MAYSHARE)
    			continue;
    
    		/*
    		 * Unmap the page from other VMAs without their own reserves.
    		 * They get marked to be SIGKILLed if they fault in these
    		 * areas. This is because a future no-page fault on this VMA
    		 * could insert a zeroed page instead of the data existing
    		 * from the time of fork. This would look like data corruption
    		 */
    		if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
    			unmap_hugepage_range(iter_vma, address,
    					     address + huge_page_size(h), page);
    	}
    	i_mmap_unlock_write(mapping);
    }
    
    /*
     * Hugetlb_cow() should be called with page lock of the original hugepage held.
     * Called with hugetlb_instantiation_mutex held and pte_page locked so we
     * cannot race with other handlers or page migration.
     * Keep the pte_same checks anyway to make transition from the mutex easier.
     */
    static vm_fault_t hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
    		       unsigned long address, pte_t *ptep,
    		       struct page *pagecache_page, spinlock_t *ptl)
    {
    	pte_t pte;
    	struct hstate *h = hstate_vma(vma);
    	struct page *old_page, *new_page;
    	int outside_reserve = 0;
    	vm_fault_t ret = 0;
    	unsigned long haddr = address & huge_page_mask(h);
    	struct mmu_notifier_range range;
    
    	pte = huge_ptep_get(ptep);
    	old_page = pte_page(pte);
    
    retry_avoidcopy:
    	/* If no-one else is actually using this page, avoid the copy
    	 * and just make the page writable */
    	if (page_mapcount(old_page) == 1 && PageAnon(old_page)) {
    		page_move_anon_rmap(old_page, vma);
    		set_huge_ptep_writable(vma, haddr, ptep);
    		return 0;
    	}
    
    	/*
    	 * If the process that created a MAP_PRIVATE mapping is about to
    	 * perform a COW due to a shared page count, attempt to satisfy
    	 * the allocation without using the existing reserves. The pagecache
    	 * page is used to determine if the reserve at this address was
    	 * consumed or not. If reserves were used, a partial faulted mapping
    	 * at the time of fork() could consume its reserves on COW instead
    	 * of the full address range.
    	 */
    	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
    			old_page != pagecache_page)
    		outside_reserve = 1;
    
    	get_page(old_page);
    
    	/*
    	 * Drop page table lock as buddy allocator may be called. It will
    	 * be acquired again before returning to the caller, as expected.
    	 */
    	spin_unlock(ptl);
    	new_page = alloc_huge_page(vma, haddr, outside_reserve);
    
    	if (IS_ERR(new_page)) {
    		/*
    		 * If a process owning a MAP_PRIVATE mapping fails to COW,
    		 * it is due to references held by a child and an insufficient
    		 * huge page pool. To guarantee the original mappers
    		 * reliability, unmap the page from child processes. The child
    		 * may get SIGKILLed if it later faults.
    		 */
    		if (outside_reserve) {
    			struct address_space *mapping = vma->vm_file->f_mapping;
    			pgoff_t idx;
    			u32 hash;
    
    			put_page(old_page);
    			BUG_ON(huge_pte_none(pte));
    			/*
    			 * Drop hugetlb_fault_mutex and i_mmap_rwsem before
    			 * unmapping.  unmapping needs to hold i_mmap_rwsem
    			 * in write mode.  Dropping i_mmap_rwsem in read mode
    			 * here is OK as COW mappings do not interact with
    			 * PMD sharing.
    			 *
    			 * Reacquire both after unmap operation.
    			 */
    			idx = vma_hugecache_offset(h, vma, haddr);
    			hash = hugetlb_fault_mutex_hash(mapping, idx);
    			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
    			i_mmap_unlock_read(mapping);
    
    			unmap_ref_private(mm, vma, old_page, haddr);
    
    			i_mmap_lock_read(mapping);
    			mutex_lock(&hugetlb_fault_mutex_table[hash]);
    			spin_lock(ptl);
    			ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
    			if (likely(ptep &&
    				   pte_same(huge_ptep_get(ptep), pte)))
    				goto retry_avoidcopy;
    			/*
    			 * race occurs while re-acquiring page table
    			 * lock, and our job is done.
    			 */
    			return 0;
    		}
    
    		ret = vmf_error(PTR_ERR(new_page));
    		goto out_release_old;
    	}
    
    	/*
    	 * When the original hugepage is shared one, it does not have
    	 * anon_vma prepared.
    	 */
    	if (unlikely(anon_vma_prepare(vma))) {
    		ret = VM_FAULT_OOM;
    		goto out_release_all;
    	}
    
    	copy_user_huge_page(new_page, old_page, address, vma,
    			    pages_per_huge_page(h));
    	__SetPageUptodate(new_page);
    
    	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, haddr,
    				haddr + huge_page_size(h));
    	mmu_notifier_invalidate_range_start(&range);
    
    	/*
    	 * Retake the page table lock to check for racing updates
    	 * before the page tables are altered
    	 */
    	spin_lock(ptl);
    	ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
    	if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {
    		ClearPagePrivate(new_page);
    
    		/* Break COW */
    		huge_ptep_clear_flush(vma, haddr, ptep);
    		mmu_notifier_invalidate_range(mm, range.start, range.end);
    		set_huge_pte_at(mm, haddr, ptep,
    				make_huge_pte(vma, new_page, 1));
    		page_remove_rmap(old_page, true);
    		hugepage_add_new_anon_rmap(new_page, vma, haddr);
    		set_page_huge_active(new_page);
    		/* Make the old page be freed below */
    		new_page = old_page;
    	}
    	spin_unlock(ptl);
    	mmu_notifier_invalidate_range_end(&range);
    out_release_all:
    	restore_reserve_on_error(h, vma, haddr, new_page);
    	put_page(new_page);
    out_release_old:
    	put_page(old_page);
    
    	spin_lock(ptl); /* Caller expects lock to be held */
    	return ret;
    }
    
    /* Return the pagecache page at a given address within a VMA */
    static struct page *hugetlbfs_pagecache_page(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long address)
    {
    	struct address_space *mapping;
    	pgoff_t idx;
    
    	mapping = vma->vm_file->f_mapping;
    	idx = vma_hugecache_offset(h, vma, address);
    
    	return find_lock_page(mapping, idx);
    }
    
    /*
     * Return whether there is a pagecache page to back given address within VMA.
     * Caller follow_hugetlb_page() holds page_table_lock so we cannot lock_page.
     */
    static bool hugetlbfs_pagecache_present(struct hstate *h,
    			struct vm_area_struct *vma, unsigned long address)
    {
    	struct address_space *mapping;
    	pgoff_t idx;
    	struct page *page;
    
    	mapping = vma->vm_file->f_mapping;
    	idx = vma_hugecache_offset(h, vma, address);
    
    	page = find_get_page(mapping, idx);
    	if (page)
    		put_page(page);
    	return page != NULL;
    }
    
    int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
    			   pgoff_t idx)
    {
    	struct inode *inode = mapping->host;
    	struct hstate *h = hstate_inode(inode);
    	int err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
    
    	if (err)
    		return err;
    	ClearPagePrivate(page);
    
    	/*
    	 * set page dirty so that it will not be removed from cache/file
    	 * by non-hugetlbfs specific code paths.
    	 */
    	set_page_dirty(page);
    
    	spin_lock(&inode->i_lock);
    	inode->i_blocks += blocks_per_huge_page(h);
    	spin_unlock(&inode->i_lock);
    	return 0;
    }
    
    static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
    			struct vm_area_struct *vma,
    			struct address_space *mapping, pgoff_t idx,
    			unsigned long address, pte_t *ptep, unsigned int flags)
    {
    	struct hstate *h = hstate_vma(vma);
    	vm_fault_t ret = VM_FAULT_SIGBUS;
    	int anon_rmap = 0;
    	unsigned long size;
    	struct page *page;
    	pte_t new_pte;
    	spinlock_t *ptl;
    	unsigned long haddr = address & huge_page_mask(h);
    	bool new_page = false;
    
    	/*
    	 * Currently, we are forced to kill the process in the event the
    	 * original mapper has unmapped pages from the child due to a failed
    	 * COW. Warn that such a situation has occurred as it may not be obvious
    	 */
    	if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {
    		pr_warn_ratelimited("PID %d killed due to inadequate hugepage pool\n",
    			   current->pid);
    		return ret;
    	}
    
    	/*
    	 * We can not race with truncation due to holding i_mmap_rwsem.
    	 * i_size is modified when holding i_mmap_rwsem, so check here
    	 * once for faults beyond end of file.
    	 */
    	size = i_size_read(mapping->host) >> huge_page_shift(h);
    	if (idx >= size)
    		goto out;
    
    retry:
    	page = find_lock_page(mapping, idx);
    	if (!page) {
    		/*
    		 * Check for page in userfault range
    		 */
    		if (userfaultfd_missing(vma)) {
    			u32 hash;
    			struct vm_fault vmf = {
    				.vma = vma,
    				.address = haddr,
    				.flags = flags,
    				/*
    				 * Hard to debug if it ends up being
    				 * used by a callee that assumes
    				 * something about the other
    				 * uninitialized fields... same as in
    				 * memory.c
    				 */
    			};
    
    			/*
    			 * hugetlb_fault_mutex and i_mmap_rwsem must be
    			 * dropped before handling userfault.  Reacquire
    			 * after handling fault to make calling code simpler.
    			 */
    			hash = hugetlb_fault_mutex_hash(mapping, idx);
    			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
    			i_mmap_unlock_read(mapping);
    			ret = handle_userfault(&vmf, VM_UFFD_MISSING);
    			i_mmap_lock_read(mapping);
    			mutex_lock(&hugetlb_fault_mutex_table[hash]);
    			goto out;
    		}
    
    		page = alloc_huge_page(vma, haddr, 0);
    		if (IS_ERR(page)) {
    			/*
    			 * Returning error will result in faulting task being
    			 * sent SIGBUS.  The hugetlb fault mutex prevents two
    			 * tasks from racing to fault in the same page which
    			 * could result in false unable to allocate errors.
    			 * Page migration does not take the fault mutex, but
    			 * does a clear then write of pte's under page table
    			 * lock.  Page fault code could race with migration,
    			 * notice the clear pte and try to allocate a page
    			 * here.  Before returning error, get ptl and make
    			 * sure there really is no pte entry.
    			 */
    			ptl = huge_pte_lock(h, mm, ptep);
    			if (!huge_pte_none(huge_ptep_get(ptep))) {
    				ret = 0;
    				spin_unlock(ptl);
    				goto out;
    			}
    			spin_unlock(ptl);
    			ret = vmf_error(PTR_ERR(page));
    			goto out;
    		}
    		clear_huge_page(page, address, pages_per_huge_page(h));
    		__SetPageUptodate(page);
    		new_page = true;
    
    		if (vma->vm_flags & VM_MAYSHARE) {
    			int err = huge_add_to_page_cache(page, mapping, idx);
    			if (err) {
    				put_page(page);
    				if (err == -EEXIST)
    					goto retry;
    				goto out;
    			}
    		} else {
    			lock_page(page);
    			if (unlikely(anon_vma_prepare(vma))) {
    				ret = VM_FAULT_OOM;
    				goto backout_unlocked;
    			}
    			anon_rmap = 1;
    		}
    	} else {
    		/*
    		 * If memory error occurs between mmap() and fault, some process
    		 * don't have hwpoisoned swap entry for errored virtual address.
    		 * So we need to block hugepage fault by PG_hwpoison bit check.
    		 */
    		if (unlikely(PageHWPoison(page))) {
    			ret = VM_FAULT_HWPOISON_LARGE |
    				VM_FAULT_SET_HINDEX(hstate_index(h));
    			goto backout_unlocked;
    		}
    	}
    
    	/*
    	 * If we are going to COW a private mapping later, we examine the
    	 * pending reservations for this page now. This will ensure that
    	 * any allocations necessary to record that reservation occur outside
    	 * the spinlock.
    	 */
    	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
    		if (vma_needs_reservation(h, vma, haddr) < 0) {
    			ret = VM_FAULT_OOM;
    			goto backout_unlocked;
    		}
    		/* Just decrements count, does not deallocate */
    		vma_end_reservation(h, vma, haddr);
    	}
    
    	ptl = huge_pte_lock(h, mm, ptep);
    	ret = 0;
    	if (!huge_pte_none(huge_ptep_get(ptep)))
    		goto backout;
    
    	if (anon_rmap) {
    		ClearPagePrivate(page);
    		hugepage_add_new_anon_rmap(page, vma, haddr);
    	} else
    		page_dup_rmap(page, true);
    	new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
    				&& (vma->vm_flags & VM_SHARED)));
    	set_huge_pte_at(mm, haddr, ptep, new_pte);
    
    	hugetlb_count_add(pages_per_huge_page(h), mm);
    	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
    		/* Optimization, do the COW without a second fault */
    		ret = hugetlb_cow(mm, vma, address, ptep, page, ptl);
    	}
    
    	spin_unlock(ptl);
    
    	/*
    	 * Only make newly allocated pages active.  Existing pages found
    	 * in the pagecache could be !page_huge_active() if they have been
    	 * isolated for migration.
    	 */
    	if (new_page)
    		set_page_huge_active(page);
    
    	unlock_page(page);
    out:
    	return ret;
    
    backout:
    	spin_unlock(ptl);
    backout_unlocked:
    	unlock_page(page);
    	restore_reserve_on_error(h, vma, haddr, page);
    	put_page(page);
    	goto out;
    }
    
    #ifdef CONFIG_SMP
    u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx)
    {
    	unsigned long key[2];
    	u32 hash;
    
    	key[0] = (unsigned long) mapping;
    	key[1] = idx;
    
    	hash = jhash2((u32 *)&key, sizeof(key)/(sizeof(u32)), 0);
    
    	return hash & (num_fault_mutexes - 1);
    }
    #else
    /*
     * For uniprocesor systems we always use a single mutex, so just
     * return 0 and avoid the hashing overhead.
     */
    u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx)
    {
    	return 0;
    }
    #endif
    
    vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
    			unsigned long address, unsigned int flags)
    {
    	pte_t *ptep, entry;
    	spinlock_t *ptl;
    	vm_fault_t ret;
    	u32 hash;
    	pgoff_t idx;
    	struct page *page = NULL;
    	struct page *pagecache_page = NULL;
    	struct hstate *h = hstate_vma(vma);
    	struct address_space *mapping;
    	int need_wait_lock = 0;
    	unsigned long haddr = address & huge_page_mask(h);
    
    	ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
    	if (ptep) {
    		/*
    		 * Since we hold no locks, ptep could be stale.  That is
    		 * OK as we are only making decisions based on content and
    		 * not actually modifying content here.
    		 */
    		entry = huge_ptep_get(ptep);
    		if (unlikely(is_hugetlb_entry_migration(entry))) {
    			migration_entry_wait_huge(vma, mm, ptep);
    			return 0;
    		} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
    			return VM_FAULT_HWPOISON_LARGE |
    				VM_FAULT_SET_HINDEX(hstate_index(h));
    	}
    
    	/*
    	 * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold
    	 * until finished with ptep.  This serves two purposes:
    	 * 1) It prevents huge_pmd_unshare from being called elsewhere
    	 *    and making the ptep no longer valid.
    	 * 2) It synchronizes us with i_size modifications during truncation.
    	 *
    	 * ptep could have already be assigned via huge_pte_offset.  That
    	 * is OK, as huge_pte_alloc will return the same value unless
    	 * something has changed.
    	 */
    	mapping = vma->vm_file->f_mapping;
    	i_mmap_lock_read(mapping);
    	ptep = huge_pte_alloc(mm, haddr, huge_page_size(h));
    	if (!ptep) {
    		i_mmap_unlock_read(mapping);
    		return VM_FAULT_OOM;
    	}
    
    	/*
    	 * Serialize hugepage allocation and instantiation, so that we don't
    	 * get spurious allocation failures if two CPUs race to instantiate
    	 * the same page in the page cache.
    	 */
    	idx = vma_hugecache_offset(h, vma, haddr);
    	hash = hugetlb_fault_mutex_hash(mapping, idx);
    	mutex_lock(&hugetlb_fault_mutex_table[hash]);
    
    	entry = huge_ptep_get(ptep);
    	if (huge_pte_none(entry)) {
    		ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, flags);
    		goto out_mutex;
    	}
    
    	ret = 0;
    
    	/*
    	 * entry could be a migration/hwpoison entry at this point, so this
    	 * check prevents the kernel from going below assuming that we have
    	 * an active hugepage in pagecache. This goto expects the 2nd page
    	 * fault, and is_hugetlb_entry_(migration|hwpoisoned) check will
    	 * properly handle it.
    	 */
    	if (!pte_present(entry))
    		goto out_mutex;
    
    	/*
    	 * If we are going to COW the mapping later, we examine the pending
    	 * reservations for this page now. This will ensure that any
    	 * allocations necessary to record that reservation occur outside the
    	 * spinlock. For private mappings, we also lookup the pagecache
    	 * page now as it is used to determine if a reservation has been
    	 * consumed.
    	 */
    	if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
    		if (vma_needs_reservation(h, vma, haddr) < 0) {
    			ret = VM_FAULT_OOM;
    			goto out_mutex;
    		}
    		/* Just decrements count, does not deallocate */
    		vma_end_reservation(h, vma, haddr);
    
    		if (!(vma->vm_flags & VM_MAYSHARE))
    			pagecache_page = hugetlbfs_pagecache_page(h,
    								vma, haddr);
    	}
    
    	ptl = huge_pte_lock(h, mm, ptep);
    
    	/* Check for a racing update before calling hugetlb_cow */
    	if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
    		goto out_ptl;
    
    	/*
    	 * hugetlb_cow() requires page locks of pte_page(entry) and
    	 * pagecache_page, so here we need take the former one
    	 * when page != pagecache_page or !pagecache_page.
    	 */
    	page = pte_page(entry);
    	if (page != pagecache_page)
    		if (!trylock_page(page)) {
    			need_wait_lock = 1;
    			goto out_ptl;
    		}
    
    	get_page(page);
    
    	if (flags & FAULT_FLAG_WRITE) {
    		if (!huge_pte_write(entry)) {
    			ret = hugetlb_cow(mm, vma, address, ptep,
    					  pagecache_page, ptl);
    			goto out_put_page;
    		}
    		entry = huge_pte_mkdirty(entry);
    	}
    	entry = pte_mkyoung(entry);
    	if (huge_ptep_set_access_flags(vma, haddr, ptep, entry,
    						flags & FAULT_FLAG_WRITE))
    		update_mmu_cache(vma, haddr, ptep);
    out_put_page:
    	if (page != pagecache_page)
    		unlock_page(page);
    	put_page(page);
    out_ptl:
    	spin_unlock(ptl);
    
    	if (pagecache_page) {
    		unlock_page(pagecache_page);
    		put_page(pagecache_page);
    	}
    out_mutex:
    	mutex_unlock(&hugetlb_fault_mutex_table[hash]);
    	i_mmap_unlock_read(mapping);
    	/*
    	 * Generally it's safe to hold refcount during waiting page lock. But
    	 * here we just wait to defer the next page fault to avoid busy loop and
    	 * the page is not used after unlocked before returning from the current
    	 * page fault. So we are safe from accessing freed page, even if we wait
    	 * here without taking refcount.
    	 */
    	if (need_wait_lock)
    		wait_on_page_locked(page);
    	return ret;
    }
    
    /*
     * Used by userfaultfd UFFDIO_COPY.  Based on mcopy_atomic_pte with
     * modifications for huge pages.
     */
    int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
    			    pte_t *dst_pte,
    			    struct vm_area_struct *dst_vma,
    			    unsigned long dst_addr,
    			    unsigned long src_addr,
    			    struct page **pagep)
    {
    	struct address_space *mapping;
    	pgoff_t idx;
    	unsigned long size;
    	int vm_shared = dst_vma->vm_flags & VM_SHARED;
    	struct hstate *h = hstate_vma(dst_vma);
    	pte_t _dst_pte;
    	spinlock_t *ptl;
    	int ret;
    	struct page *page;
    
    	if (!*pagep) {
    		ret = -ENOMEM;
    		page = alloc_huge_page(dst_vma, dst_addr, 0);
    		if (IS_ERR(page))
    			goto out;
    
    		ret = copy_huge_page_from_user(page,
    						(const void __user *) src_addr,
    						pages_per_huge_page(h), false);
    
    		/* fallback to copy_from_user outside mmap_lock */
    		if (unlikely(ret)) {
    			ret = -ENOENT;
    			*pagep = page;
    			/* don't free the page */
    			goto out;
    		}
    	} else {
    		page = *pagep;
    		*pagep = NULL;
    	}
    
    	/*
    	 * The memory barrier inside __SetPageUptodate makes sure that
    	 * preceding stores to the page contents become visible before
    	 * the set_pte_at() write.
    	 */
    	__SetPageUptodate(page);
    
    	mapping = dst_vma->vm_file->f_mapping;
    	idx = vma_hugecache_offset(h, dst_vma, dst_addr);
    
    	/*
    	 * If shared, add to page cache
    	 */
    	if (vm_shared) {
    		size = i_size_read(mapping->host) >> huge_page_shift(h);
    		ret = -EFAULT;
    		if (idx >= size)
    			goto out_release_nounlock;
    
    		/*
    		 * Serialization between remove_inode_hugepages() and
    		 * huge_add_to_page_cache() below happens through the
    		 * hugetlb_fault_mutex_table that here must be hold by
    		 * the caller.
    		 */
    		ret = huge_add_to_page_cache(page, mapping, idx);
    		if (ret)
    			goto out_release_nounlock;
    	}
    
    	ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
    	spin_lock(ptl);
    
    	/*
    	 * Recheck the i_size after holding PT lock to make sure not
    	 * to leave any page mapped (as page_mapped()) beyond the end
    	 * of the i_size (remove_inode_hugepages() is strict about
    	 * enforcing that). If we bail out here, we'll also leave a
    	 * page in the radix tree in the vm_shared case beyond the end
    	 * of the i_size, but remove_inode_hugepages() will take care
    	 * of it as soon as we drop the hugetlb_fault_mutex_table.
    	 */
    	size = i_size_read(mapping->host) >> huge_page_shift(h);
    	ret = -EFAULT;
    	if (idx >= size)
    		goto out_release_unlock;
    
    	ret = -EEXIST;
    	if (!huge_pte_none(huge_ptep_get(dst_pte)))
    		goto out_release_unlock;
    
    	if (vm_shared) {
    		page_dup_rmap(page, true);
    	} else {
    		ClearPagePrivate(page);
    		hugepage_add_new_anon_rmap(page, dst_vma, dst_addr);
    	}
    
    	_dst_pte = make_huge_pte(dst_vma, page, dst_vma->vm_flags & VM_WRITE);
    	if (dst_vma->vm_flags & VM_WRITE)
    		_dst_pte = huge_pte_mkdirty(_dst_pte);
    	_dst_pte = pte_mkyoung(_dst_pte);
    
    	set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
    
    	(void)huge_ptep_set_access_flags(dst_vma, dst_addr, dst_pte, _dst_pte,
    					dst_vma->vm_flags & VM_WRITE);
    	hugetlb_count_add(pages_per_huge_page(h), dst_mm);
    
    	/* No need to invalidate - it was non-present before */
    	update_mmu_cache(dst_vma, dst_addr, dst_pte);
    
    	spin_unlock(ptl);
    	set_page_huge_active(page);
    	if (vm_shared)
    		unlock_page(page);
    	ret = 0;
    out:
    	return ret;
    out_release_unlock:
    	spin_unlock(ptl);
    	if (vm_shared)
    		unlock_page(page);
    out_release_nounlock:
    	put_page(page);
    	goto out;
    }
    
    long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
    			 struct page **pages, struct vm_area_struct **vmas,
    			 unsigned long *position, unsigned long *nr_pages,
    			 long i, unsigned int flags, int *locked)
    {
    	unsigned long pfn_offset;
    	unsigned long vaddr = *position;
    	unsigned long remainder = *nr_pages;
    	struct hstate *h = hstate_vma(vma);
    	int err = -EFAULT;
    
    	while (vaddr < vma->vm_end && remainder) {
    		pte_t *pte;
    		spinlock_t *ptl = NULL;
    		int absent;
    		struct page *page;
    
    		/*
    		 * If we have a pending SIGKILL, don't keep faulting pages and
    		 * potentially allocating memory.
    		 */
    		if (fatal_signal_pending(current)) {
    			remainder = 0;
    			break;
    		}
    
    		/*
    		 * Some archs (sparc64, sh*) have multiple pte_ts to
    		 * each hugepage.  We have to make sure we get the
    		 * first, for the page indexing below to work.
    		 *
    		 * Note that page table lock is not held when pte is null.
    		 */
    		pte = huge_pte_offset(mm, vaddr & huge_page_mask(h),
    				      huge_page_size(h));
    		if (pte)
    			ptl = huge_pte_lock(h, mm, pte);
    		absent = !pte || huge_pte_none(huge_ptep_get(pte));
    
    		/*
    		 * When coredumping, it suits get_dump_page if we just return
    		 * an error where there's an empty slot with no huge pagecache
    		 * to back it.  This way, we avoid allocating a hugepage, and
    		 * the sparse dumpfile avoids allocating disk blocks, but its
    		 * huge holes still show up with zeroes where they need to be.
    		 */
    		if (absent && (flags & FOLL_DUMP) &&
    		    !hugetlbfs_pagecache_present(h, vma, vaddr)) {
    			if (pte)
    				spin_unlock(ptl);
    			remainder = 0;
    			break;
    		}
    
    		/*
    		 * We need call hugetlb_fault for both hugepages under migration
    		 * (in which case hugetlb_fault waits for the migration,) and
    		 * hwpoisoned hugepages (in which case we need to prevent the
    		 * caller from accessing to them.) In order to do this, we use
    		 * here is_swap_pte instead of is_hugetlb_entry_migration and
    		 * is_hugetlb_entry_hwpoisoned. This is because it simply covers
    		 * both cases, and because we can't follow correct pages
    		 * directly from any kind of swap entries.
    		 */
    		if (absent || is_swap_pte(huge_ptep_get(pte)) ||
    		    ((flags & FOLL_WRITE) &&
    		      !huge_pte_write(huge_ptep_get(pte)))) {
    			vm_fault_t ret;
    			unsigned int fault_flags = 0;
    
    			if (pte)
    				spin_unlock(ptl);
    			if (flags & FOLL_WRITE)
    				fault_flags |= FAULT_FLAG_WRITE;
    			if (locked)
    				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
    					FAULT_FLAG_KILLABLE;
    			if (flags & FOLL_NOWAIT)
    				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
    					FAULT_FLAG_RETRY_NOWAIT;
    			if (flags & FOLL_TRIED) {
    				/*
    				 * Note: FAULT_FLAG_ALLOW_RETRY and
    				 * FAULT_FLAG_TRIED can co-exist
    				 */
    				fault_flags |= FAULT_FLAG_TRIED;
    			}
    			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);
    			if (ret & VM_FAULT_ERROR) {
    				err = vm_fault_to_errno(ret, flags);
    				remainder = 0;
    				break;
    			}
    			if (ret & VM_FAULT_RETRY) {
    				if (locked &&
    				    !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
    					*locked = 0;
    				*nr_pages = 0;
    				/*
    				 * VM_FAULT_RETRY must not return an
    				 * error, it will return zero
    				 * instead.
    				 *
    				 * No need to update "position" as the
    				 * caller will not check it after
    				 * *nr_pages is set to 0.
    				 */
    				return i;
    			}
    			continue;
    		}
    
    		pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
    		page = pte_page(huge_ptep_get(pte));
    
    		/*
    		 * If subpage information not requested, update counters
    		 * and skip the same_page loop below.
    		 */
    		if (!pages && !vmas && !pfn_offset &&
    		    (vaddr + huge_page_size(h) < vma->vm_end) &&
    		    (remainder >= pages_per_huge_page(h))) {
    			vaddr += huge_page_size(h);
    			remainder -= pages_per_huge_page(h);
    			i += pages_per_huge_page(h);
    			spin_unlock(ptl);
    			continue;
    		}
    
    same_page:
    		if (pages) {
    			pages[i] = mem_map_offset(page, pfn_offset);
    			/*
    			 * try_grab_page() should always succeed here, because:
    			 * a) we hold the ptl lock, and b) we've just checked
    			 * that the huge page is present in the page tables. If
    			 * the huge page is present, then the tail pages must
    			 * also be present. The ptl prevents the head page and
    			 * tail pages from being rearranged in any way. So this
    			 * page must be available at this point, unless the page
    			 * refcount overflowed:
    			 */
    			if (WARN_ON_ONCE(!try_grab_page(pages[i], flags))) {
    				spin_unlock(ptl);
    				remainder = 0;
    				err = -ENOMEM;
    				break;
    			}
    		}
    
    		if (vmas)
    			vmas[i] = vma;
    
    		vaddr += PAGE_SIZE;
    		++pfn_offset;
    		--remainder;
    		++i;
    		if (vaddr < vma->vm_end && remainder &&
    				pfn_offset < pages_per_huge_page(h)) {
    			/*
    			 * We use pfn_offset to avoid touching the pageframes
    			 * of this compound page.
    			 */
    			goto same_page;
    		}
    		spin_unlock(ptl);
    	}
    	*nr_pages = remainder;
    	/*
    	 * setting position is actually required only if remainder is
    	 * not zero but it's faster not to add a "if (remainder)"
    	 * branch.
    	 */
    	*position = vaddr;
    
    	return i ? i : err;
    }
    
    #ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE
    /*
     * ARCHes with special requirements for evicting HUGETLB backing TLB entries can
     * implement this.
     */
    #define flush_hugetlb_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
    #endif
    
    unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
    		unsigned long address, unsigned long end, pgprot_t newprot)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	unsigned long start = address;
    	pte_t *ptep;
    	pte_t pte;
    	struct hstate *h = hstate_vma(vma);
    	unsigned long pages = 0;
    	bool shared_pmd = false;
    	struct mmu_notifier_range range;
    
    	/*
    	 * In the case of shared PMDs, the area to flush could be beyond
    	 * start/end.  Set range.start/range.end to cover the maximum possible
    	 * range if PMD sharing is possible.
    	 */
    	mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA,
    				0, vma, mm, start, end);
    	adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
    
    	BUG_ON(address >= end);
    	flush_cache_range(vma, range.start, range.end);
    
    	mmu_notifier_invalidate_range_start(&range);
    	i_mmap_lock_write(vma->vm_file->f_mapping);
    	for (; address < end; address += huge_page_size(h)) {
    		spinlock_t *ptl;
    		ptep = huge_pte_offset(mm, address, huge_page_size(h));
    		if (!ptep)
    			continue;
    		ptl = huge_pte_lock(h, mm, ptep);
    		if (huge_pmd_unshare(mm, vma, &address, ptep)) {
    			pages++;
    			spin_unlock(ptl);
    			shared_pmd = true;
    			continue;
    		}
    		pte = huge_ptep_get(ptep);
    		if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
    			spin_unlock(ptl);
    			continue;
    		}
    		if (unlikely(is_hugetlb_entry_migration(pte))) {
    			swp_entry_t entry = pte_to_swp_entry(pte);
    
    			if (is_write_migration_entry(entry)) {
    				pte_t newpte;
    
    				make_migration_entry_read(&entry);
    				newpte = swp_entry_to_pte(entry);
    				set_huge_swap_pte_at(mm, address, ptep,
    						     newpte, huge_page_size(h));
    				pages++;
    			}
    			spin_unlock(ptl);
    			continue;
    		}
    		if (!huge_pte_none(pte)) {
    			pte_t old_pte;
    
    			old_pte = huge_ptep_modify_prot_start(vma, address, ptep);
    			pte = pte_mkhuge(huge_pte_modify(old_pte, newprot));
    			pte = arch_make_huge_pte(pte, vma, NULL, 0);
    			huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
    			pages++;
    		}
    		spin_unlock(ptl);
    	}
    	/*
    	 * Must flush TLB before releasing i_mmap_rwsem: x86's huge_pmd_unshare
    	 * may have cleared our pud entry and done put_page on the page table:
    	 * once we release i_mmap_rwsem, another task can do the final put_page
    	 * and that page table be reused and filled with junk.  If we actually
    	 * did unshare a page of pmds, flush the range corresponding to the pud.
    	 */
    	if (shared_pmd)
    		flush_hugetlb_tlb_range(vma, range.start, range.end);
    	else
    		flush_hugetlb_tlb_range(vma, start, end);
    	/*
    	 * No need to call mmu_notifier_invalidate_range() we are downgrading
    	 * page table protection not changing it to point to a new page.
    	 *
    	 * See Documentation/vm/mmu_notifier.rst
    	 */
    	i_mmap_unlock_write(vma->vm_file->f_mapping);
    	mmu_notifier_invalidate_range_end(&range);
    
    	return pages << h->order;
    }
    
    int hugetlb_reserve_pages(struct inode *inode,
    					long from, long to,
    					struct vm_area_struct *vma,
    					vm_flags_t vm_flags)
    {
    	long ret, chg, add = -1;
    	struct hstate *h = hstate_inode(inode);
    	struct hugepage_subpool *spool = subpool_inode(inode);
    	struct resv_map *resv_map;
    	struct hugetlb_cgroup *h_cg = NULL;
    	long gbl_reserve, regions_needed = 0;
    
    	/* This should never happen */
    	if (from > to) {
    		VM_WARN(1, "%s called with a negative range\n", __func__);
    		return -EINVAL;
    	}
    
    	/*
    	 * Only apply hugepage reservation if asked. At fault time, an
    	 * attempt will be made for VM_NORESERVE to allocate a page
    	 * without using reserves
    	 */
    	if (vm_flags & VM_NORESERVE)
    		return 0;
    
    	/*
    	 * Shared mappings base their reservation on the number of pages that
    	 * are already allocated on behalf of the file. Private mappings need
    	 * to reserve the full area even if read-only as mprotect() may be
    	 * called to make the mapping read-write. Assume !vma is a shm mapping
    	 */
    	if (!vma || vma->vm_flags & VM_MAYSHARE) {
    		/*
    		 * resv_map can not be NULL as hugetlb_reserve_pages is only
    		 * called for inodes for which resv_maps were created (see
    		 * hugetlbfs_get_inode).
    		 */
    		resv_map = inode_resv_map(inode);
    
    		chg = region_chg(resv_map, from, to, &regions_needed);
    
    	} else {
    		/* Private mapping. */
    		resv_map = resv_map_alloc();
    		if (!resv_map)
    			return -ENOMEM;
    
    		chg = to - from;
    
    		set_vma_resv_map(vma, resv_map);
    		set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
    	}
    
    	if (chg < 0) {
    		ret = chg;
    		goto out_err;
    	}
    
    	ret = hugetlb_cgroup_charge_cgroup_rsvd(
    		hstate_index(h), chg * pages_per_huge_page(h), &h_cg);
    
    	if (ret < 0) {
    		ret = -ENOMEM;
    		goto out_err;
    	}
    
    	if (vma && !(vma->vm_flags & VM_MAYSHARE) && h_cg) {
    		/* For private mappings, the hugetlb_cgroup uncharge info hangs
    		 * of the resv_map.
    		 */
    		resv_map_set_hugetlb_cgroup_uncharge_info(resv_map, h_cg, h);
    	}
    
    	/*
    	 * There must be enough pages in the subpool for the mapping. If
    	 * the subpool has a minimum size, there may be some global
    	 * reservations already in place (gbl_reserve).
    	 */
    	gbl_reserve = hugepage_subpool_get_pages(spool, chg);
    	if (gbl_reserve < 0) {
    		ret = -ENOSPC;
    		goto out_uncharge_cgroup;
    	}
    
    	/*
    	 * Check enough hugepages are available for the reservation.
    	 * Hand the pages back to the subpool if there are not
    	 */
    	ret = hugetlb_acct_memory(h, gbl_reserve);
    	if (ret < 0) {
    		goto out_put_pages;
    	}
    
    	/*
    	 * Account for the reservations made. Shared mappings record regions
    	 * that have reservations as they are shared by multiple VMAs.
    	 * When the last VMA disappears, the region map says how much
    	 * the reservation was and the page cache tells how much of
    	 * the reservation was consumed. Private mappings are per-VMA and
    	 * only the consumed reservations are tracked. When the VMA
    	 * disappears, the original reservation is the VMA size and the
    	 * consumed reservations are stored in the map. Hence, nothing
    	 * else has to be done for private mappings here
    	 */
    	if (!vma || vma->vm_flags & VM_MAYSHARE) {
    		add = region_add(resv_map, from, to, regions_needed, h, h_cg);
    
    		if (unlikely(add < 0)) {
    			hugetlb_acct_memory(h, -gbl_reserve);
    			ret = add;
    			goto out_put_pages;
    		} else if (unlikely(chg > add)) {
    			/*
    			 * pages in this range were added to the reserve
    			 * map between region_chg and region_add.  This
    			 * indicates a race with alloc_huge_page.  Adjust
    			 * the subpool and reserve counts modified above
    			 * based on the difference.
    			 */
    			long rsv_adjust;
    
    			hugetlb_cgroup_uncharge_cgroup_rsvd(
    				hstate_index(h),
    				(chg - add) * pages_per_huge_page(h), h_cg);
    
    			rsv_adjust = hugepage_subpool_put_pages(spool,
    								chg - add);
    			hugetlb_acct_memory(h, -rsv_adjust);
    		}
    	}
    	return 0;
    out_put_pages:
    	/* put back original number of pages, chg */
    	(void)hugepage_subpool_put_pages(spool, chg);
    out_uncharge_cgroup:
    	hugetlb_cgroup_uncharge_cgroup_rsvd(hstate_index(h),
    					    chg * pages_per_huge_page(h), h_cg);
    out_err:
    	if (!vma || vma->vm_flags & VM_MAYSHARE)
    		/* Only call region_abort if the region_chg succeeded but the
    		 * region_add failed or didn't run.
    		 */
    		if (chg >= 0 && add < 0)
    			region_abort(resv_map, from, to, regions_needed);
    	if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
    		kref_put(&resv_map->refs, resv_map_release);
    	return ret;
    }
    
    long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
    								long freed)
    {
    	struct hstate *h = hstate_inode(inode);
    	struct resv_map *resv_map = inode_resv_map(inode);
    	long chg = 0;
    	struct hugepage_subpool *spool = subpool_inode(inode);
    	long gbl_reserve;
    
    	/*
    	 * Since this routine can be called in the evict inode path for all
    	 * hugetlbfs inodes, resv_map could be NULL.
    	 */
    	if (resv_map) {
    		chg = region_del(resv_map, start, end);
    		/*
    		 * region_del() can fail in the rare case where a region
    		 * must be split and another region descriptor can not be
    		 * allocated.  If end == LONG_MAX, it will not fail.
    		 */
    		if (chg < 0)
    			return chg;
    	}
    
    	spin_lock(&inode->i_lock);
    	inode->i_blocks -= (blocks_per_huge_page(h) * freed);
    	spin_unlock(&inode->i_lock);
    
    	/*
    	 * If the subpool has a minimum size, the number of global
    	 * reservations to be released may be adjusted.
    	 */
    	gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed));
    	hugetlb_acct_memory(h, -gbl_reserve);
    
    	return 0;
    }
    
    #ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
    static unsigned long page_table_shareable(struct vm_area_struct *svma,
    				struct vm_area_struct *vma,
    				unsigned long addr, pgoff_t idx)
    {
    	unsigned long saddr = ((idx - svma->vm_pgoff) << PAGE_SHIFT) +
    				svma->vm_start;
    	unsigned long sbase = saddr & PUD_MASK;
    	unsigned long s_end = sbase + PUD_SIZE;
    
    	/* Allow segments to share if only one is marked locked */
    	unsigned long vm_flags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
    	unsigned long svm_flags = svma->vm_flags & VM_LOCKED_CLEAR_MASK;
    
    	/*
    	 * match the virtual addresses, permission and the alignment of the
    	 * page table page.
    	 */
    	if (pmd_index(addr) != pmd_index(saddr) ||
    	    vm_flags != svm_flags ||
    	    sbase < svma->vm_start || svma->vm_end < s_end)
    		return 0;
    
    	return saddr;
    }
    
    static bool vma_shareable(struct vm_area_struct *vma, unsigned long addr)
    {
    	unsigned long base = addr & PUD_MASK;
    	unsigned long end = base + PUD_SIZE;
    
    	/*
    	 * check on proper vm_flags and page table alignment
    	 */
    	if (vma->vm_flags & VM_MAYSHARE && range_in_vma(vma, base, end))
    		return true;
    	return false;
    }
    
    /*
     * Determine if start,end range within vma could be mapped by shared pmd.
     * If yes, adjust start and end to cover range associated with possible
     * shared pmd mappings.
     */
    void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
    				unsigned long *start, unsigned long *end)
    {
    	unsigned long a_start, a_end;
    
    	if (!(vma->vm_flags & VM_MAYSHARE))
    		return;
    
    	/* Extend the range to be PUD aligned for a worst case scenario */
    	a_start = ALIGN_DOWN(*start, PUD_SIZE);
    	a_end = ALIGN(*end, PUD_SIZE);
    
    	/*
    	 * Intersect the range with the vma range, since pmd sharing won't be
    	 * across vma after all
    	 */
    	*start = max(vma->vm_start, a_start);
    	*end = min(vma->vm_end, a_end);
    }
    
    /*
     * Search for a shareable pmd page for hugetlb. In any case calls pmd_alloc()
     * and returns the corresponding pte. While this is not necessary for the
     * !shared pmd case because we can allocate the pmd later as well, it makes the
     * code much cleaner.
     *
     * This routine must be called with i_mmap_rwsem held in at least read mode if
     * sharing is possible.  For hugetlbfs, this prevents removal of any page
     * table entries associated with the address space.  This is important as we
     * are setting up sharing based on existing page table entries (mappings).
     *
     * NOTE: This routine is only called from huge_pte_alloc.  Some callers of
     * huge_pte_alloc know that sharing is not possible and do not take
     * i_mmap_rwsem as a performance optimization.  This is handled by the
     * if !vma_shareable check at the beginning of the routine. i_mmap_rwsem is
     * only required for subsequent processing.
     */
    pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
    {
    	struct vm_area_struct *vma = find_vma(mm, addr);
    	struct address_space *mapping = vma->vm_file->f_mapping;
    	pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
    			vma->vm_pgoff;
    	struct vm_area_struct *svma;
    	unsigned long saddr;
    	pte_t *spte = NULL;
    	pte_t *pte;
    	spinlock_t *ptl;
    
    	if (!vma_shareable(vma, addr))
    		return (pte_t *)pmd_alloc(mm, pud, addr);
    
    	i_mmap_assert_locked(mapping);
    	vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
    		if (svma == vma)
    			continue;
    
    		saddr = page_table_shareable(svma, vma, addr, idx);
    		if (saddr) {
    			spte = huge_pte_offset(svma->vm_mm, saddr,
    					       vma_mmu_pagesize(svma));
    			if (spte) {
    				get_page(virt_to_page(spte));
    				break;
    			}
    		}
    	}
    
    	if (!spte)
    		goto out;
    
    	ptl = huge_pte_lock(hstate_vma(vma), mm, spte);
    	if (pud_none(*pud)) {
    		pud_populate(mm, pud,
    				(pmd_t *)((unsigned long)spte & PAGE_MASK));
    		mm_inc_nr_pmds(mm);
    	} else {
    		put_page(virt_to_page(spte));
    	}
    	spin_unlock(ptl);
    out:
    	pte = (pte_t *)pmd_alloc(mm, pud, addr);
    	return pte;
    }
    
    /*
     * unmap huge page backed by shared pte.
     *
     * Hugetlb pte page is ref counted at the time of mapping.  If pte is shared
     * indicated by page_count > 1, unmap is achieved by clearing pud and
     * decrementing the ref count. If count == 1, the pte page is not shared.
     *
     * Called with page table lock held and i_mmap_rwsem held in write mode.
     *
     * returns: 1 successfully unmapped a shared pte page
     *	    0 the underlying pte page is not shared, or it is the last user
     */
    int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
    					unsigned long *addr, pte_t *ptep)
    {
    	pgd_t *pgd = pgd_offset(mm, *addr);
    	p4d_t *p4d = p4d_offset(pgd, *addr);
    	pud_t *pud = pud_offset(p4d, *addr);
    
    	i_mmap_assert_write_locked(vma->vm_file->f_mapping);
    	BUG_ON(page_count(virt_to_page(ptep)) == 0);
    	if (page_count(virt_to_page(ptep)) == 1)
    		return 0;
    
    	pud_clear(pud);
    	put_page(virt_to_page(ptep));
    	mm_dec_nr_pmds(mm);
    	*addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
    	return 1;
    }
    #define want_pmd_share()	(1)
    #else /* !CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
    pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
    {
    	return NULL;
    }
    
    int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
    				unsigned long *addr, pte_t *ptep)
    {
    	return 0;
    }
    
    void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
    				unsigned long *start, unsigned long *end)
    {
    }
    #define want_pmd_share()	(0)
    #endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
    
    #ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
    pte_t *huge_pte_alloc(struct mm_struct *mm,
    			unsigned long addr, unsigned long sz)
    {
    	pgd_t *pgd;
    	p4d_t *p4d;
    	pud_t *pud;
    	pte_t *pte = NULL;
    
    	pgd = pgd_offset(mm, addr);
    	p4d = p4d_alloc(mm, pgd, addr);
    	if (!p4d)
    		return NULL;
    	pud = pud_alloc(mm, p4d, addr);
    	if (pud) {
    		if (sz == PUD_SIZE) {
    			pte = (pte_t *)pud;
    		} else {
    			BUG_ON(sz != PMD_SIZE);
    			if (want_pmd_share() && pud_none(*pud))
    				pte = huge_pmd_share(mm, addr, pud);
    			else
    				pte = (pte_t *)pmd_alloc(mm, pud, addr);
    		}
    	}
    	BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte));
    
    	return pte;
    }
    
    /*
     * huge_pte_offset() - Walk the page table to resolve the hugepage
     * entry at address @addr
     *
     * Return: Pointer to page table entry (PUD or PMD) for
     * address @addr, or NULL if a !p*d_present() entry is encountered and the
     * size @sz doesn't match the hugepage size at this level of the page
     * table.
     */
    pte_t *huge_pte_offset(struct mm_struct *mm,
    		       unsigned long addr, unsigned long sz)
    {
    	pgd_t *pgd;
    	p4d_t *p4d;
    	pud_t *pud;
    	pmd_t *pmd;
    
    	pgd = pgd_offset(mm, addr);
    	if (!pgd_present(*pgd))
    		return NULL;
    	p4d = p4d_offset(pgd, addr);
    	if (!p4d_present(*p4d))
    		return NULL;
    
    	pud = pud_offset(p4d, addr);
    	if (sz == PUD_SIZE)
    		/* must be pud huge, non-present or none */
    		return (pte_t *)pud;
    	if (!pud_present(*pud))
    		return NULL;
    	/* must have a valid entry and size to go further */
    
    	pmd = pmd_offset(pud, addr);
    	/* must be pmd huge, non-present or none */
    	return (pte_t *)pmd;
    }
    
    #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
    
    /*
     * These functions are overwritable if your architecture needs its own
     * behavior.
     */
    struct page * __weak
    follow_huge_addr(struct mm_struct *mm, unsigned long address,
    			      int write)
    {
    	return ERR_PTR(-EINVAL);
    }
    
    struct page * __weak
    follow_huge_pd(struct vm_area_struct *vma,
    	       unsigned long address, hugepd_t hpd, int flags, int pdshift)
    {
    	WARN(1, "hugepd follow called with no support for hugepage directory format\n");
    	return NULL;
    }
    
    struct page * __weak
    follow_huge_pmd(struct mm_struct *mm, unsigned long address,
    		pmd_t *pmd, int flags)
    {
    	struct page *page = NULL;
    	spinlock_t *ptl;
    	pte_t pte;
    
    	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
    	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
    			 (FOLL_PIN | FOLL_GET)))
    		return NULL;
    
    retry:
    	ptl = pmd_lockptr(mm, pmd);
    	spin_lock(ptl);
    	/*
    	 * make sure that the address range covered by this pmd is not
    	 * unmapped from other threads.
    	 */
    	if (!pmd_huge(*pmd))
    		goto out;
    	pte = huge_ptep_get((pte_t *)pmd);
    	if (pte_present(pte)) {
    		page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
    		/*
    		 * try_grab_page() should always succeed here, because: a) we
    		 * hold the pmd (ptl) lock, and b) we've just checked that the
    		 * huge pmd (head) page is present in the page tables. The ptl
    		 * prevents the head page and tail pages from being rearranged
    		 * in any way. So this page must be available at this point,
    		 * unless the page refcount overflowed:
    		 */
    		if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
    			page = NULL;
    			goto out;
    		}
    	} else {
    		if (is_hugetlb_entry_migration(pte)) {
    			spin_unlock(ptl);
    			__migration_entry_wait(mm, (pte_t *)pmd, ptl);
    			goto retry;
    		}
    		/*
    		 * hwpoisoned entry is treated as no_page_table in
    		 * follow_page_mask().
    		 */
    	}
    out:
    	spin_unlock(ptl);
    	return page;
    }
    
    struct page * __weak
    follow_huge_pud(struct mm_struct *mm, unsigned long address,
    		pud_t *pud, int flags)
    {
    	if (flags & (FOLL_GET | FOLL_PIN))
    		return NULL;
    
    	return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
    }
    
    struct page * __weak
    follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags)
    {
    	if (flags & (FOLL_GET | FOLL_PIN))
    		return NULL;
    
    	return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
    }
    
    bool isolate_huge_page(struct page *page, struct list_head *list)
    {
    	bool ret = true;
    
    	spin_lock(&hugetlb_lock);
    	if (!PageHeadHuge(page) || !page_huge_active(page) ||
    	    !get_page_unless_zero(page)) {
    		ret = false;
    		goto unlock;
    	}
    	clear_page_huge_active(page);
    	list_move_tail(&page->lru, list);
    unlock:
    	spin_unlock(&hugetlb_lock);
    	return ret;
    }
    
    void putback_active_hugepage(struct page *page)
    {
    	VM_BUG_ON_PAGE(!PageHead(page), page);
    	spin_lock(&hugetlb_lock);
    	set_page_huge_active(page);
    	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
    	spin_unlock(&hugetlb_lock);
    	put_page(page);
    }
    
    void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
    {
    	struct hstate *h = page_hstate(oldpage);
    
    	hugetlb_cgroup_migrate(oldpage, newpage);
    	set_page_owner_migrate_reason(newpage, reason);
    
    	/*
    	 * transfer temporary state of the new huge page. This is
    	 * reverse to other transitions because the newpage is going to
    	 * be final while the old one will be freed so it takes over
    	 * the temporary status.
    	 *
    	 * Also note that we have to transfer the per-node surplus state
    	 * here as well otherwise the global surplus count will not match
    	 * the per-node's.
    	 */
    	if (PageHugeTemporary(newpage)) {
    		int old_nid = page_to_nid(oldpage);
    		int new_nid = page_to_nid(newpage);
    
    		SetPageHugeTemporary(oldpage);
    		ClearPageHugeTemporary(newpage);
    
    		spin_lock(&hugetlb_lock);
    		if (h->surplus_huge_pages_node[old_nid]) {
    			h->surplus_huge_pages_node[old_nid]--;
    			h->surplus_huge_pages_node[new_nid]++;
    		}
    		spin_unlock(&hugetlb_lock);
    	}
    }
    
    #ifdef CONFIG_CMA
    static bool cma_reserve_called __initdata;
    
    static int __init cmdline_parse_hugetlb_cma(char *p)
    {
    	hugetlb_cma_size = memparse(p, &p);
    	return 0;
    }
    
    early_param("hugetlb_cma", cmdline_parse_hugetlb_cma);
    
    void __init hugetlb_cma_reserve(int order)
    {
    	unsigned long size, reserved, per_node;
    	int nid;
    
    	cma_reserve_called = true;
    
    	if (!hugetlb_cma_size)
    		return;
    
    	if (hugetlb_cma_size < (PAGE_SIZE << order)) {
    		pr_warn("hugetlb_cma: cma area should be at least %lu MiB\n",
    			(PAGE_SIZE << order) / SZ_1M);
    		return;
    	}
    
    	/*
    	 * If 3 GB area is requested on a machine with 4 numa nodes,
    	 * let's allocate 1 GB on first three nodes and ignore the last one.
    	 */
    	per_node = DIV_ROUND_UP(hugetlb_cma_size, nr_online_nodes);
    	pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n",
    		hugetlb_cma_size / SZ_1M, per_node / SZ_1M);
    
    	reserved = 0;
    	for_each_node_state(nid, N_ONLINE) {
    		int res;
    		char name[CMA_MAX_NAME];
    
    		size = min(per_node, hugetlb_cma_size - reserved);
    		size = round_up(size, PAGE_SIZE << order);
    
    		snprintf(name, sizeof(name), "hugetlb%d", nid);
    		res = cma_declare_contiguous_nid(0, size, 0, PAGE_SIZE << order,
    						 0, false, name,
    						 &hugetlb_cma[nid], nid);
    		if (res) {
    			pr_warn("hugetlb_cma: reservation failed: err %d, node %d",
    				res, nid);
    			continue;
    		}
    
    		reserved += size;
    		pr_info("hugetlb_cma: reserved %lu MiB on node %d\n",
    			size / SZ_1M, nid);
    
    		if (reserved >= hugetlb_cma_size)
    			break;
    	}
    }
    
    void __init hugetlb_cma_check(void)
    {
    	if (!hugetlb_cma_size || cma_reserve_called)
    		return;
    
    	pr_warn("hugetlb_cma: the option isn't supported by current arch\n");
    }
    
    #endif /* CONFIG_CMA */