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dmaengine.c

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  • migrate.c 47.33 KiB
    /*
     * Memory Migration functionality - linux/mm/migrate.c
     *
     * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
     *
     * Page migration was first developed in the context of the memory hotplug
     * project. The main authors of the migration code are:
     *
     * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
     * Hirokazu Takahashi <taka@valinux.co.jp>
     * Dave Hansen <haveblue@us.ibm.com>
     * Christoph Lameter
     */
    
    #include <linux/migrate.h>
    #include <linux/export.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    #include <linux/pagemap.h>
    #include <linux/buffer_head.h>
    #include <linux/mm_inline.h>
    #include <linux/nsproxy.h>
    #include <linux/pagevec.h>
    #include <linux/ksm.h>
    #include <linux/rmap.h>
    #include <linux/topology.h>
    #include <linux/cpu.h>
    #include <linux/cpuset.h>
    #include <linux/writeback.h>
    #include <linux/mempolicy.h>
    #include <linux/vmalloc.h>
    #include <linux/security.h>
    #include <linux/syscalls.h>
    #include <linux/hugetlb.h>
    #include <linux/hugetlb_cgroup.h>
    #include <linux/gfp.h>
    #include <linux/balloon_compaction.h>
    #include <linux/mmu_notifier.h>
    #include <linux/page_idle.h>
    
    #include <asm/tlbflush.h>
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/migrate.h>
    
    #include "internal.h"
    
    /*
     * migrate_prep() needs to be called before we start compiling a list of pages
     * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
     * undesirable, use migrate_prep_local()
     */
    int migrate_prep(void)
    {
    	/*
    	 * Clear the LRU lists so pages can be isolated.
    	 * Note that pages may be moved off the LRU after we have
    	 * drained them. Those pages will fail to migrate like other
    	 * pages that may be busy.
    	 */
    	lru_add_drain_all();
    
    	return 0;
    }
    
    /* Do the necessary work of migrate_prep but not if it involves other CPUs */
    int migrate_prep_local(void)
    {
    	lru_add_drain();
    
    	return 0;
    }
    
    /*
     * Put previously isolated pages back onto the appropriate lists
     * from where they were once taken off for compaction/migration.
     *
     * This function shall be used whenever the isolated pageset has been
     * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
     * and isolate_huge_page().
     */
    void putback_movable_pages(struct list_head *l)
    {
    	struct page *page;
    	struct page *page2;
    
    	list_for_each_entry_safe(page, page2, l, lru) {
    		if (unlikely(PageHuge(page))) {
    			putback_active_hugepage(page);
    			continue;
    		}
    		list_del(&page->lru);
    		dec_zone_page_state(page, NR_ISOLATED_ANON +
    				page_is_file_cache(page));
    		if (unlikely(isolated_balloon_page(page)))
    			balloon_page_putback(page);
    		else
    			putback_lru_page(page);
    	}
    }
    
    /*
     * Restore a potential migration pte to a working pte entry
     */
    static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
    				 unsigned long addr, void *old)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	swp_entry_t entry;
     	pmd_t *pmd;
    	pte_t *ptep, pte;
     	spinlock_t *ptl;
    
    	if (unlikely(PageHuge(new))) {
    		ptep = huge_pte_offset(mm, addr);
    		if (!ptep)
    			goto out;
    		ptl = huge_pte_lockptr(hstate_vma(vma), mm, ptep);
    	} else {
    		pmd = mm_find_pmd(mm, addr);
    		if (!pmd)
    			goto out;
    
    		ptep = pte_offset_map(pmd, addr);
    
    		/*
    		 * Peek to check is_swap_pte() before taking ptlock?  No, we
    		 * can race mremap's move_ptes(), which skips anon_vma lock.
    		 */
    
    		ptl = pte_lockptr(mm, pmd);
    	}
    
     	spin_lock(ptl);
    	pte = *ptep;
    	if (!is_swap_pte(pte))
    		goto unlock;
    
    	entry = pte_to_swp_entry(pte);
    
    	if (!is_migration_entry(entry) ||
    	    migration_entry_to_page(entry) != old)
    		goto unlock;
    
    	get_page(new);
    	pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
    	if (pte_swp_soft_dirty(*ptep))
    		pte = pte_mksoft_dirty(pte);
    
    	/* Recheck VMA as permissions can change since migration started  */
    	if (is_write_migration_entry(entry))
    		pte = maybe_mkwrite(pte, vma);
    
    #ifdef CONFIG_HUGETLB_PAGE
    	if (PageHuge(new)) {
    		pte = pte_mkhuge(pte);
    		pte = arch_make_huge_pte(pte, vma, new, 0);
    	}
    #endif
    	flush_dcache_page(new);
    	set_pte_at(mm, addr, ptep, pte);
    
    	if (PageHuge(new)) {
    		if (PageAnon(new))
    			hugepage_add_anon_rmap(new, vma, addr);
    		else
    			page_dup_rmap(new);
    	} else if (PageAnon(new))
    		page_add_anon_rmap(new, vma, addr);
    	else
    		page_add_file_rmap(new);
    
    	if (vma->vm_flags & VM_LOCKED)
    		mlock_vma_page(new);
    
    	/* No need to invalidate - it was non-present before */
    	update_mmu_cache(vma, addr, ptep);
    unlock:
    	pte_unmap_unlock(ptep, ptl);
    out:
    	return SWAP_AGAIN;
    }
    
    /*
     * Get rid of all migration entries and replace them by
     * references to the indicated page.
     */
    static void remove_migration_ptes(struct page *old, struct page *new)
    {
    	struct rmap_walk_control rwc = {
    		.rmap_one = remove_migration_pte,
    		.arg = old,
    	};
    
    	rmap_walk(new, &rwc);
    }
    
    /*
     * Something used the pte of a page under migration. We need to
     * get to the page and wait until migration is finished.
     * When we return from this function the fault will be retried.
     */
    void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
    				spinlock_t *ptl)
    {
    	pte_t pte;
    	swp_entry_t entry;
    	struct page *page;
    
    	spin_lock(ptl);
    	pte = *ptep;
    	if (!is_swap_pte(pte))
    		goto out;
    
    	entry = pte_to_swp_entry(pte);
    	if (!is_migration_entry(entry))
    		goto out;
    
    	page = migration_entry_to_page(entry);
    
    	/*
    	 * Once radix-tree replacement of page migration started, page_count
    	 * *must* be zero. And, we don't want to call wait_on_page_locked()
    	 * against a page without get_page().
    	 * So, we use get_page_unless_zero(), here. Even failed, page fault
    	 * will occur again.
    	 */
    	if (!get_page_unless_zero(page))
    		goto out;
    	pte_unmap_unlock(ptep, ptl);
    	wait_on_page_locked(page);
    	put_page(page);
    	return;
    out:
    	pte_unmap_unlock(ptep, ptl);
    }
    
    void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
    				unsigned long address)
    {
    	spinlock_t *ptl = pte_lockptr(mm, pmd);
    	pte_t *ptep = pte_offset_map(pmd, address);
    	__migration_entry_wait(mm, ptep, ptl);
    }
    
    void migration_entry_wait_huge(struct vm_area_struct *vma,
    		struct mm_struct *mm, pte_t *pte)
    {
    	spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
    	__migration_entry_wait(mm, pte, ptl);
    }
    
    #ifdef CONFIG_BLOCK
    /* Returns true if all buffers are successfully locked */
    static bool buffer_migrate_lock_buffers(struct buffer_head *head,
    							enum migrate_mode mode)
    {
    	struct buffer_head *bh = head;
    
    	/* Simple case, sync compaction */
    	if (mode != MIGRATE_ASYNC) {
    		do {
    			get_bh(bh);
    			lock_buffer(bh);
    			bh = bh->b_this_page;
    
    		} while (bh != head);
    
    		return true;
    	}
    
    	/* async case, we cannot block on lock_buffer so use trylock_buffer */
    	do {
    		get_bh(bh);
    		if (!trylock_buffer(bh)) {
    			/*
    			 * We failed to lock the buffer and cannot stall in
    			 * async migration. Release the taken locks
    			 */
    			struct buffer_head *failed_bh = bh;
    			put_bh(failed_bh);
    			bh = head;
    			while (bh != failed_bh) {
    				unlock_buffer(bh);
    				put_bh(bh);
    				bh = bh->b_this_page;
    			}
    			return false;
    		}
    
    		bh = bh->b_this_page;
    	} while (bh != head);
    	return true;
    }
    #else
    static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
    							enum migrate_mode mode)
    {
    	return true;
    }
    #endif /* CONFIG_BLOCK */
    
    /*
     * Replace the page in the mapping.
     *
     * The number of remaining references must be:
     * 1 for anonymous pages without a mapping
     * 2 for pages with a mapping
     * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
     */
    int migrate_page_move_mapping(struct address_space *mapping,
    		struct page *newpage, struct page *page,
    		struct buffer_head *head, enum migrate_mode mode,
    		int extra_count)
    {
    	int expected_count = 1 + extra_count;
    	void **pslot;
    
    	if (!mapping) {
    		/* Anonymous page without mapping */
    		if (page_count(page) != expected_count)
    			return -EAGAIN;
    		return MIGRATEPAGE_SUCCESS;
    	}
    
    	spin_lock_irq(&mapping->tree_lock);
    
    	pslot = radix_tree_lookup_slot(&mapping->page_tree,
     					page_index(page));
    
    	expected_count += 1 + page_has_private(page);
    	if (page_count(page) != expected_count ||
    		radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return -EAGAIN;
    	}
    
    	if (!page_freeze_refs(page, expected_count)) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return -EAGAIN;
    	}
    
    	/*
    	 * In the async migration case of moving a page with buffers, lock the
    	 * buffers using trylock before the mapping is moved. If the mapping
    	 * was moved, we later failed to lock the buffers and could not move
    	 * the mapping back due to an elevated page count, we would have to
    	 * block waiting on other references to be dropped.
    	 */
    	if (mode == MIGRATE_ASYNC && head &&
    			!buffer_migrate_lock_buffers(head, mode)) {
    		page_unfreeze_refs(page, expected_count);
    		spin_unlock_irq(&mapping->tree_lock);
    		return -EAGAIN;
    	}
    
    	/*
    	 * Now we know that no one else is looking at the page.
    	 */
    	get_page(newpage);	/* add cache reference */
    	if (PageSwapCache(page)) {
    		SetPageSwapCache(newpage);
    		set_page_private(newpage, page_private(page));
    	}
    
    	radix_tree_replace_slot(pslot, newpage);
    
    	/*
    	 * Drop cache reference from old page by unfreezing
    	 * to one less reference.
    	 * We know this isn't the last reference.
    	 */
    	page_unfreeze_refs(page, expected_count - 1);
    
    	/*
    	 * If moved to a different zone then also account
    	 * the page for that zone. Other VM counters will be
    	 * taken care of when we establish references to the
    	 * new page and drop references to the old page.
    	 *
    	 * Note that anonymous pages are accounted for
    	 * via NR_FILE_PAGES and NR_ANON_PAGES if they
    	 * are mapped to swap space.
    	 */
    	__dec_zone_page_state(page, NR_FILE_PAGES);
    	__inc_zone_page_state(newpage, NR_FILE_PAGES);
    	if (!PageSwapCache(page) && PageSwapBacked(page)) {
    		__dec_zone_page_state(page, NR_SHMEM);
    		__inc_zone_page_state(newpage, NR_SHMEM);
    	}
    	spin_unlock_irq(&mapping->tree_lock);
    
    	return MIGRATEPAGE_SUCCESS;
    }
    
    /*
     * The expected number of remaining references is the same as that
     * of migrate_page_move_mapping().
     */
    int migrate_huge_page_move_mapping(struct address_space *mapping,
    				   struct page *newpage, struct page *page)
    {
    	int expected_count;
    	void **pslot;
    
    	if (!mapping) {
    		if (page_count(page) != 1)
    			return -EAGAIN;
    		return MIGRATEPAGE_SUCCESS;
    	}
    
    	spin_lock_irq(&mapping->tree_lock);
    
    	pslot = radix_tree_lookup_slot(&mapping->page_tree,
    					page_index(page));
    
    	expected_count = 2 + page_has_private(page);
    	if (page_count(page) != expected_count ||
    		radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return -EAGAIN;
    	}
    
    	if (!page_freeze_refs(page, expected_count)) {
    		spin_unlock_irq(&mapping->tree_lock);
    		return -EAGAIN;
    	}
    
    	get_page(newpage);
    
    	radix_tree_replace_slot(pslot, newpage);
    
    	page_unfreeze_refs(page, expected_count - 1);
    
    	spin_unlock_irq(&mapping->tree_lock);
    	return MIGRATEPAGE_SUCCESS;
    }
    
    /*
     * Gigantic pages are so large that we do not guarantee that page++ pointer
     * arithmetic will work across the entire page.  We need something more
     * specialized.
     */
    static void __copy_gigantic_page(struct page *dst, struct page *src,
    				int nr_pages)
    {
    	int i;
    	struct page *dst_base = dst;
    	struct page *src_base = src;
    
    	for (i = 0; i < nr_pages; ) {
    		cond_resched();
    		copy_highpage(dst, src);
    
    		i++;
    		dst = mem_map_next(dst, dst_base, i);
    		src = mem_map_next(src, src_base, i);
    	}
    }
    
    static void copy_huge_page(struct page *dst, struct page *src)
    {
    	int i;
    	int nr_pages;
    
    	if (PageHuge(src)) {
    		/* hugetlbfs page */
    		struct hstate *h = page_hstate(src);
    		nr_pages = pages_per_huge_page(h);
    
    		if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
    			__copy_gigantic_page(dst, src, nr_pages);
    			return;
    		}
    	} else {
    		/* thp page */
    		BUG_ON(!PageTransHuge(src));
    		nr_pages = hpage_nr_pages(src);
    	}
    
    	for (i = 0; i < nr_pages; i++) {
    		cond_resched();
    		copy_highpage(dst + i, src + i);
    	}
    }
    
    /*
     * Copy the page to its new location
     */
    void migrate_page_copy(struct page *newpage, struct page *page)
    {
    	int cpupid;
    
    	if (PageHuge(page) || PageTransHuge(page))
    		copy_huge_page(newpage, page);
    	else
    		copy_highpage(newpage, page);
    
    	if (PageError(page))
    		SetPageError(newpage);
    	if (PageReferenced(page))
    		SetPageReferenced(newpage);
    	if (PageUptodate(page))
    		SetPageUptodate(newpage);
    	if (TestClearPageActive(page)) {
    		VM_BUG_ON_PAGE(PageUnevictable(page), page);
    		SetPageActive(newpage);
    	} else if (TestClearPageUnevictable(page))
    		SetPageUnevictable(newpage);
    	if (PageChecked(page))
    		SetPageChecked(newpage);
    	if (PageMappedToDisk(page))
    		SetPageMappedToDisk(newpage);
    
    	if (PageDirty(page)) {
    		clear_page_dirty_for_io(page);
    		/*
    		 * Want to mark the page and the radix tree as dirty, and
    		 * redo the accounting that clear_page_dirty_for_io undid,
    		 * but we can't use set_page_dirty because that function
    		 * is actually a signal that all of the page has become dirty.
    		 * Whereas only part of our page may be dirty.
    		 */
    		if (PageSwapBacked(page))
    			SetPageDirty(newpage);
    		else
    			__set_page_dirty_nobuffers(newpage);
     	}
    
    	if (page_is_young(page))
    		set_page_young(newpage);
    	if (page_is_idle(page))
    		set_page_idle(newpage);
    
    	/*
    	 * Copy NUMA information to the new page, to prevent over-eager
    	 * future migrations of this same page.
    	 */
    	cpupid = page_cpupid_xchg_last(page, -1);
    	page_cpupid_xchg_last(newpage, cpupid);
    
    	ksm_migrate_page(newpage, page);
    	/*
    	 * Please do not reorder this without considering how mm/ksm.c's
    	 * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
    	 */
    	if (PageSwapCache(page))
    		ClearPageSwapCache(page);
    	ClearPagePrivate(page);
    	set_page_private(page, 0);
    
    	/*
    	 * If any waiters have accumulated on the new page then
    	 * wake them up.
    	 */
    	if (PageWriteback(newpage))
    		end_page_writeback(newpage);
    }
    
    /************************************************************
     *                    Migration functions
     ***********************************************************/
    
    /*
     * Common logic to directly migrate a single page suitable for
     * pages that do not use PagePrivate/PagePrivate2.
     *
     * Pages are locked upon entry and exit.
     */
    int migrate_page(struct address_space *mapping,
    		struct page *newpage, struct page *page,
    		enum migrate_mode mode)
    {
    	int rc;
    
    	BUG_ON(PageWriteback(page));	/* Writeback must be complete */
    
    	rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
    
    	if (rc != MIGRATEPAGE_SUCCESS)
    		return rc;
    
    	migrate_page_copy(newpage, page);
    	return MIGRATEPAGE_SUCCESS;
    }
    EXPORT_SYMBOL(migrate_page);
    
    #ifdef CONFIG_BLOCK
    /*
     * Migration function for pages with buffers. This function can only be used
     * if the underlying filesystem guarantees that no other references to "page"
     * exist.
     */
    int buffer_migrate_page(struct address_space *mapping,
    		struct page *newpage, struct page *page, enum migrate_mode mode)
    {
    	struct buffer_head *bh, *head;
    	int rc;
    
    	if (!page_has_buffers(page))
    		return migrate_page(mapping, newpage, page, mode);
    
    	head = page_buffers(page);
    
    	rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
    
    	if (rc != MIGRATEPAGE_SUCCESS)
    		return rc;
    
    	/*
    	 * In the async case, migrate_page_move_mapping locked the buffers
    	 * with an IRQ-safe spinlock held. In the sync case, the buffers
    	 * need to be locked now
    	 */
    	if (mode != MIGRATE_ASYNC)
    		BUG_ON(!buffer_migrate_lock_buffers(head, mode));
    
    	ClearPagePrivate(page);
    	set_page_private(newpage, page_private(page));
    	set_page_private(page, 0);
    	put_page(page);
    	get_page(newpage);
    
    	bh = head;
    	do {
    		set_bh_page(bh, newpage, bh_offset(bh));
    		bh = bh->b_this_page;
    
    	} while (bh != head);
    
    	SetPagePrivate(newpage);
    
    	migrate_page_copy(newpage, page);
    
    	bh = head;
    	do {
    		unlock_buffer(bh);
     		put_bh(bh);
    		bh = bh->b_this_page;
    
    	} while (bh != head);
    
    	return MIGRATEPAGE_SUCCESS;
    }
    EXPORT_SYMBOL(buffer_migrate_page);
    #endif
    
    /*
     * Writeback a page to clean the dirty state
     */
    static int writeout(struct address_space *mapping, struct page *page)
    {
    	struct writeback_control wbc = {
    		.sync_mode = WB_SYNC_NONE,
    		.nr_to_write = 1,
    		.range_start = 0,
    		.range_end = LLONG_MAX,
    		.for_reclaim = 1
    	};
    	int rc;
    
    	if (!mapping->a_ops->writepage)
    		/* No write method for the address space */
    		return -EINVAL;
    
    	if (!clear_page_dirty_for_io(page))
    		/* Someone else already triggered a write */
    		return -EAGAIN;
    
    	/*
    	 * A dirty page may imply that the underlying filesystem has
    	 * the page on some queue. So the page must be clean for
    	 * migration. Writeout may mean we loose the lock and the
    	 * page state is no longer what we checked for earlier.
    	 * At this point we know that the migration attempt cannot
    	 * be successful.
    	 */
    	remove_migration_ptes(page, page);
    
    	rc = mapping->a_ops->writepage(page, &wbc);
    
    	if (rc != AOP_WRITEPAGE_ACTIVATE)
    		/* unlocked. Relock */
    		lock_page(page);
    
    	return (rc < 0) ? -EIO : -EAGAIN;
    }
    
    /*
     * Default handling if a filesystem does not provide a migration function.
     */
    static int fallback_migrate_page(struct address_space *mapping,
    	struct page *newpage, struct page *page, enum migrate_mode mode)
    {
    	if (PageDirty(page)) {
    		/* Only writeback pages in full synchronous migration */
    		if (mode != MIGRATE_SYNC)
    			return -EBUSY;
    		return writeout(mapping, page);
    	}
    
    	/*
    	 * Buffers may be managed in a filesystem specific way.
    	 * We must have no buffers or drop them.
    	 */
    	if (page_has_private(page) &&
    	    !try_to_release_page(page, GFP_KERNEL))
    		return -EAGAIN;
    
    	return migrate_page(mapping, newpage, page, mode);
    }
    
    /*
     * Move a page to a newly allocated page
     * The page is locked and all ptes have been successfully removed.
     *
     * The new page will have replaced the old page if this function
     * is successful.
     *
     * Return value:
     *   < 0 - error code
     *  MIGRATEPAGE_SUCCESS - success
     */
    static int move_to_new_page(struct page *newpage, struct page *page,
    				int page_was_mapped, enum migrate_mode mode)
    {
    	struct address_space *mapping;
    	int rc;
    
    	/*
    	 * Block others from accessing the page when we get around to
    	 * establishing additional references. We are the only one
    	 * holding a reference to the new page at this point.
    	 */
    	if (!trylock_page(newpage))
    		BUG();
    
    	/* Prepare mapping for the new page.*/
    	newpage->index = page->index;
    	newpage->mapping = page->mapping;
    	if (PageSwapBacked(page))
    		SetPageSwapBacked(newpage);
    
    	/*
    	 * Indirectly called below, migrate_page_copy() copies PG_dirty and thus
    	 * needs newpage's memcg set to transfer memcg dirty page accounting.
    	 * So perform memcg migration in two steps:
    	 * 1. set newpage->mem_cgroup (here)
    	 * 2. clear page->mem_cgroup (below)
    	 */
    	set_page_memcg(newpage, page_memcg(page));
    
    	mapping = page_mapping(page);
    	if (!mapping)
    		rc = migrate_page(mapping, newpage, page, mode);
    	else if (mapping->a_ops->migratepage)
    		/*
    		 * Most pages have a mapping and most filesystems provide a
    		 * migratepage callback. Anonymous pages are part of swap
    		 * space which also has its own migratepage callback. This
    		 * is the most common path for page migration.
    		 */
    		rc = mapping->a_ops->migratepage(mapping,
    						newpage, page, mode);
    	else
    		rc = fallback_migrate_page(mapping, newpage, page, mode);
    
    	if (rc != MIGRATEPAGE_SUCCESS) {
    		set_page_memcg(newpage, NULL);
    		newpage->mapping = NULL;
    	} else {
    		set_page_memcg(page, NULL);
    		if (page_was_mapped)
    			remove_migration_ptes(page, newpage);
    		page->mapping = NULL;
    	}
    
    	unlock_page(newpage);
    
    	return rc;
    }
    
    static int __unmap_and_move(struct page *page, struct page *newpage,
    				int force, enum migrate_mode mode)
    {
    	int rc = -EAGAIN;
    	int page_was_mapped = 0;
    	struct anon_vma *anon_vma = NULL;
    
    	if (!trylock_page(page)) {
    		if (!force || mode == MIGRATE_ASYNC)
    			goto out;
    
    		/*
    		 * It's not safe for direct compaction to call lock_page.
    		 * For example, during page readahead pages are added locked
    		 * to the LRU. Later, when the IO completes the pages are
    		 * marked uptodate and unlocked. However, the queueing
    		 * could be merging multiple pages for one bio (e.g.
    		 * mpage_readpages). If an allocation happens for the
    		 * second or third page, the process can end up locking
    		 * the same page twice and deadlocking. Rather than
    		 * trying to be clever about what pages can be locked,
    		 * avoid the use of lock_page for direct compaction
    		 * altogether.
    		 */
    		if (current->flags & PF_MEMALLOC)
    			goto out;
    
    		lock_page(page);
    	}
    
    	if (PageWriteback(page)) {
    		/*
    		 * Only in the case of a full synchronous migration is it
    		 * necessary to wait for PageWriteback. In the async case,
    		 * the retry loop is too short and in the sync-light case,
    		 * the overhead of stalling is too much
    		 */
    		if (mode != MIGRATE_SYNC) {
    			rc = -EBUSY;
    			goto out_unlock;
    		}
    		if (!force)
    			goto out_unlock;
    		wait_on_page_writeback(page);
    	}
    	/*
    	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
    	 * we cannot notice that anon_vma is freed while we migrates a page.
    	 * This get_anon_vma() delays freeing anon_vma pointer until the end
    	 * of migration. File cache pages are no problem because of page_lock()
    	 * File Caches may use write_page() or lock_page() in migration, then,
    	 * just care Anon page here.
    	 */
    	if (PageAnon(page) && !PageKsm(page)) {
    		/*
    		 * Only page_lock_anon_vma_read() understands the subtleties of
    		 * getting a hold on an anon_vma from outside one of its mms.
    		 */
    		anon_vma = page_get_anon_vma(page);
    		if (anon_vma) {
    			/*
    			 * Anon page
    			 */
    		} else if (PageSwapCache(page)) {
    			/*
    			 * We cannot be sure that the anon_vma of an unmapped
    			 * swapcache page is safe to use because we don't
    			 * know in advance if the VMA that this page belonged
    			 * to still exists. If the VMA and others sharing the
    			 * data have been freed, then the anon_vma could
    			 * already be invalid.
    			 *
    			 * To avoid this possibility, swapcache pages get
    			 * migrated but are not remapped when migration
    			 * completes
    			 */
    		} else {
    			goto out_unlock;
    		}
    	}
    
    	if (unlikely(isolated_balloon_page(page))) {
    		/*
    		 * A ballooned page does not need any special attention from
    		 * physical to virtual reverse mapping procedures.
    		 * Skip any attempt to unmap PTEs or to remap swap cache,
    		 * in order to avoid burning cycles at rmap level, and perform
    		 * the page migration right away (proteced by page lock).
    		 */
    		rc = balloon_page_migrate(newpage, page, mode);
    		goto out_unlock;
    	}
    
    	/*
    	 * Corner case handling:
    	 * 1. When a new swap-cache page is read into, it is added to the LRU
    	 * and treated as swapcache but it has no rmap yet.
    	 * Calling try_to_unmap() against a page->mapping==NULL page will
    	 * trigger a BUG.  So handle it here.
    	 * 2. An orphaned page (see truncate_complete_page) might have
    	 * fs-private metadata. The page can be picked up due to memory
    	 * offlining.  Everywhere else except page reclaim, the page is
    	 * invisible to the vm, so the page can not be migrated.  So try to
    	 * free the metadata, so the page can be freed.
    	 */
    	if (!page->mapping) {
    		VM_BUG_ON_PAGE(PageAnon(page), page);
    		if (page_has_private(page)) {
    			try_to_free_buffers(page);
    			goto out_unlock;
    		}
    		goto skip_unmap;
    	}
    
    	/* Establish migration ptes or remove ptes */
    	if (page_mapped(page)) {
    		try_to_unmap(page,
    			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
    		page_was_mapped = 1;
    	}
    
    skip_unmap:
    	if (!page_mapped(page))
    		rc = move_to_new_page(newpage, page, page_was_mapped, mode);
    
    	if (rc && page_was_mapped)
    		remove_migration_ptes(page, page);
    
    	/* Drop an anon_vma reference if we took one */
    	if (anon_vma)
    		put_anon_vma(anon_vma);
    
    out_unlock:
    	unlock_page(page);
    out:
    	return rc;
    }
    
    /*
     * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
     * around it.
     */
    #if (GCC_VERSION >= 40700 && GCC_VERSION < 40900) && defined(CONFIG_ARM)
    #define ICE_noinline noinline
    #else
    #define ICE_noinline
    #endif
    
    /*
     * Obtain the lock on page, remove all ptes and migrate the page
     * to the newly allocated page in newpage.
     */
    static ICE_noinline int unmap_and_move(new_page_t get_new_page,
    				   free_page_t put_new_page,
    				   unsigned long private, struct page *page,
    				   int force, enum migrate_mode mode,
    				   enum migrate_reason reason)
    {
    	int rc = 0;
    	int *result = NULL;
    	struct page *newpage = get_new_page(page, private, &result);
    
    	if (!newpage)
    		return -ENOMEM;
    
    	if (page_count(page) == 1) {
    		/* page was freed from under us. So we are done. */
    		goto out;
    	}
    
    	if (unlikely(PageTransHuge(page)))
    		if (unlikely(split_huge_page(page)))
    			goto out;
    
    	rc = __unmap_and_move(page, newpage, force, mode);
    
    out:
    	if (rc != -EAGAIN) {
    		/*
    		 * A page that has been migrated has all references
    		 * removed and will be freed. A page that has not been
    		 * migrated will have kepts its references and be
    		 * restored.
    		 */
    		list_del(&page->lru);
    		dec_zone_page_state(page, NR_ISOLATED_ANON +
    				page_is_file_cache(page));
    		/* Soft-offlined page shouldn't go through lru cache list */
    		if (reason == MR_MEMORY_FAILURE) {
    			put_page(page);
    			if (!test_set_page_hwpoison(page))
    				num_poisoned_pages_inc();
    		} else
    			putback_lru_page(page);
    	}
    
    	/*
    	 * If migration was not successful and there's a freeing callback, use
    	 * it.  Otherwise, putback_lru_page() will drop the reference grabbed
    	 * during isolation.
    	 */
    	if (rc != MIGRATEPAGE_SUCCESS && put_new_page) {
    		ClearPageSwapBacked(newpage);
    		put_new_page(newpage, private);
    	} else if (unlikely(__is_movable_balloon_page(newpage))) {
    		/* drop our reference, page already in the balloon */
    		put_page(newpage);
    	} else
    		putback_lru_page(newpage);
    
    	if (result) {
    		if (rc)
    			*result = rc;
    		else
    			*result = page_to_nid(newpage);
    	}
    	return rc;
    }
    
    /*
     * Counterpart of unmap_and_move_page() for hugepage migration.
     *
     * This function doesn't wait the completion of hugepage I/O
     * because there is no race between I/O and migration for hugepage.
     * Note that currently hugepage I/O occurs only in direct I/O
     * where no lock is held and PG_writeback is irrelevant,
     * and writeback status of all subpages are counted in the reference
     * count of the head page (i.e. if all subpages of a 2MB hugepage are
     * under direct I/O, the reference of the head page is 512 and a bit more.)
     * This means that when we try to migrate hugepage whose subpages are
     * doing direct I/O, some references remain after try_to_unmap() and
     * hugepage migration fails without data corruption.
     *
     * There is also no race when direct I/O is issued on the page under migration,
     * because then pte is replaced with migration swap entry and direct I/O code
     * will wait in the page fault for migration to complete.
     */
    static int unmap_and_move_huge_page(new_page_t get_new_page,
    				free_page_t put_new_page, unsigned long private,
    				struct page *hpage, int force,
    				enum migrate_mode mode)
    {
    	int rc = 0;
    	int *result = NULL;
    	int page_was_mapped = 0;
    	struct page *new_hpage;
    	struct anon_vma *anon_vma = NULL;
    
    	/*
    	 * Movability of hugepages depends on architectures and hugepage size.
    	 * This check is necessary because some callers of hugepage migration
    	 * like soft offline and memory hotremove don't walk through page
    	 * tables or check whether the hugepage is pmd-based or not before
    	 * kicking migration.
    	 */
    	if (!hugepage_migration_supported(page_hstate(hpage))) {
    		putback_active_hugepage(hpage);
    		return -ENOSYS;
    	}
    
    	new_hpage = get_new_page(hpage, private, &result);
    	if (!new_hpage)
    		return -ENOMEM;
    
    	rc = -EAGAIN;
    
    	if (!trylock_page(hpage)) {
    		if (!force || mode != MIGRATE_SYNC)
    			goto out;
    		lock_page(hpage);
    	}
    
    	if (PageAnon(hpage))
    		anon_vma = page_get_anon_vma(hpage);
    
    	if (page_mapped(hpage)) {
    		try_to_unmap(hpage,
    			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
    		page_was_mapped = 1;
    	}
    
    	if (!page_mapped(hpage))
    		rc = move_to_new_page(new_hpage, hpage, page_was_mapped, mode);
    
    	if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)
    		remove_migration_ptes(hpage, hpage);
    
    	if (anon_vma)
    		put_anon_vma(anon_vma);
    
    	if (rc == MIGRATEPAGE_SUCCESS)
    		hugetlb_cgroup_migrate(hpage, new_hpage);
    
    	unlock_page(hpage);
    out:
    	if (rc != -EAGAIN)
    		putback_active_hugepage(hpage);
    
    	/*
    	 * If migration was not successful and there's a freeing callback, use
    	 * it.  Otherwise, put_page() will drop the reference grabbed during
    	 * isolation.
    	 */
    	if (rc != MIGRATEPAGE_SUCCESS && put_new_page)
    		put_new_page(new_hpage, private);
    	else
    		putback_active_hugepage(new_hpage);
    
    	if (result) {
    		if (rc)
    			*result = rc;
    		else
    			*result = page_to_nid(new_hpage);
    	}
    	return rc;
    }
    
    /*
     * migrate_pages - migrate the pages specified in a list, to the free pages
     *		   supplied as the target for the page migration
     *
     * @from:		The list of pages to be migrated.
     * @get_new_page:	The function used to allocate free pages to be used
     *			as the target of the page migration.
     * @put_new_page:	The function used to free target pages if migration
     *			fails, or NULL if no special handling is necessary.
     * @private:		Private data to be passed on to get_new_page()
     * @mode:		The migration mode that specifies the constraints for
     *			page migration, if any.
     * @reason:		The reason for page migration.
     *
     * The function returns after 10 attempts or if no pages are movable any more
     * because the list has become empty or no retryable pages exist any more.
     * The caller should call putback_movable_pages() to return pages to the LRU
     * or free list only if ret != 0.
     *
     * Returns the number of pages that were not migrated, or an error code.
     */
    int migrate_pages(struct list_head *from, new_page_t get_new_page,
    		free_page_t put_new_page, unsigned long private,
    		enum migrate_mode mode, int reason)
    {
    	int retry = 1;
    	int nr_failed = 0;
    	int nr_succeeded = 0;
    	int pass = 0;
    	struct page *page;
    	struct page *page2;
    	int swapwrite = current->flags & PF_SWAPWRITE;
    	int rc;
    
    	if (!swapwrite)
    		current->flags |= PF_SWAPWRITE;
    
    	for(pass = 0; pass < 10 && retry; pass++) {
    		retry = 0;
    
    		list_for_each_entry_safe(page, page2, from, lru) {
    			cond_resched();
    
    			if (PageHuge(page))
    				rc = unmap_and_move_huge_page(get_new_page,
    						put_new_page, private, page,
    						pass > 2, mode);
    			else
    				rc = unmap_and_move(get_new_page, put_new_page,
    						private, page, pass > 2, mode,
    						reason);
    
    			switch(rc) {
    			case -ENOMEM:
    				goto out;
    			case -EAGAIN:
    				retry++;
    				break;
    			case MIGRATEPAGE_SUCCESS:
    				nr_succeeded++;
    				break;
    			default:
    				/*
    				 * Permanent failure (-EBUSY, -ENOSYS, etc.):
    				 * unlike -EAGAIN case, the failed page is
    				 * removed from migration page list and not
    				 * retried in the next outer loop.
    				 */
    				nr_failed++;
    				break;
    			}
    		}
    	}
    	nr_failed += retry;
    	rc = nr_failed;
    out:
    	if (nr_succeeded)
    		count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
    	if (nr_failed)
    		count_vm_events(PGMIGRATE_FAIL, nr_failed);
    	trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
    
    	if (!swapwrite)
    		current->flags &= ~PF_SWAPWRITE;
    
    	return rc;
    }
    
    #ifdef CONFIG_NUMA
    /*
     * Move a list of individual pages
     */
    struct page_to_node {
    	unsigned long addr;
    	struct page *page;
    	int node;
    	int status;
    };
    
    static struct page *new_page_node(struct page *p, unsigned long private,
    		int **result)
    {
    	struct page_to_node *pm = (struct page_to_node *)private;
    
    	while (pm->node != MAX_NUMNODES && pm->page != p)
    		pm++;
    
    	if (pm->node == MAX_NUMNODES)
    		return NULL;
    
    	*result = &pm->status;
    
    	if (PageHuge(p))
    		return alloc_huge_page_node(page_hstate(compound_head(p)),
    					pm->node);
    	else
    		return __alloc_pages_node(pm->node,
    				GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, 0);
    }
    
    /*
     * Move a set of pages as indicated in the pm array. The addr
     * field must be set to the virtual address of the page to be moved
     * and the node number must contain a valid target node.
     * The pm array ends with node = MAX_NUMNODES.
     */
    static int do_move_page_to_node_array(struct mm_struct *mm,
    				      struct page_to_node *pm,
    				      int migrate_all)
    {
    	int err;
    	struct page_to_node *pp;
    	LIST_HEAD(pagelist);
    
    	down_read(&mm->mmap_sem);
    
    	/*
    	 * Build a list of pages to migrate
    	 */
    	for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
    		struct vm_area_struct *vma;
    		struct page *page;
    
    		err = -EFAULT;
    		vma = find_vma(mm, pp->addr);
    		if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma))
    			goto set_status;
    
    		/* FOLL_DUMP to ignore special (like zero) pages */
    		page = follow_page(vma, pp->addr,
    				FOLL_GET | FOLL_SPLIT | FOLL_DUMP);
    
    		err = PTR_ERR(page);
    		if (IS_ERR(page))
    			goto set_status;
    
    		err = -ENOENT;
    		if (!page)
    			goto set_status;
    
    		pp->page = page;
    		err = page_to_nid(page);
    
    		if (err == pp->node)
    			/*
    			 * Node already in the right place
    			 */
    			goto put_and_set;
    
    		err = -EACCES;
    		if (page_mapcount(page) > 1 &&
    				!migrate_all)
    			goto put_and_set;
    
    		if (PageHuge(page)) {
    			if (PageHead(page))
    				isolate_huge_page(page, &pagelist);
    			goto put_and_set;
    		}
    
    		err = isolate_lru_page(page);
    		if (!err) {
    			list_add_tail(&page->lru, &pagelist);
    			inc_zone_page_state(page, NR_ISOLATED_ANON +
    					    page_is_file_cache(page));
    		}
    put_and_set:
    		/*
    		 * Either remove the duplicate refcount from
    		 * isolate_lru_page() or drop the page ref if it was
    		 * not isolated.
    		 */
    		put_page(page);
    set_status:
    		pp->status = err;
    	}
    
    	err = 0;
    	if (!list_empty(&pagelist)) {
    		err = migrate_pages(&pagelist, new_page_node, NULL,
    				(unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
    		if (err)
    			putback_movable_pages(&pagelist);
    	}
    
    	up_read(&mm->mmap_sem);
    	return err;
    }
    
    /*
     * Migrate an array of page address onto an array of nodes and fill
     * the corresponding array of status.
     */
    static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
    			 unsigned long nr_pages,
    			 const void __user * __user *pages,
    			 const int __user *nodes,
    			 int __user *status, int flags)
    {
    	struct page_to_node *pm;
    	unsigned long chunk_nr_pages;
    	unsigned long chunk_start;
    	int err;
    
    	err = -ENOMEM;
    	pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
    	if (!pm)
    		goto out;
    
    	migrate_prep();
    
    	/*
    	 * Store a chunk of page_to_node array in a page,
    	 * but keep the last one as a marker
    	 */
    	chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
    
    	for (chunk_start = 0;
    	     chunk_start < nr_pages;
    	     chunk_start += chunk_nr_pages) {
    		int j;
    
    		if (chunk_start + chunk_nr_pages > nr_pages)
    			chunk_nr_pages = nr_pages - chunk_start;
    
    		/* fill the chunk pm with addrs and nodes from user-space */
    		for (j = 0; j < chunk_nr_pages; j++) {
    			const void __user *p;
    			int node;
    
    			err = -EFAULT;
    			if (get_user(p, pages + j + chunk_start))
    				goto out_pm;
    			pm[j].addr = (unsigned long) p;
    
    			if (get_user(node, nodes + j + chunk_start))
    				goto out_pm;
    
    			err = -ENODEV;
    			if (node < 0 || node >= MAX_NUMNODES)
    				goto out_pm;
    
    			if (!node_state(node, N_MEMORY))
    				goto out_pm;
    
    			err = -EACCES;
    			if (!node_isset(node, task_nodes))
    				goto out_pm;
    
    			pm[j].node = node;
    		}
    
    		/* End marker for this chunk */
    		pm[chunk_nr_pages].node = MAX_NUMNODES;
    
    		/* Migrate this chunk */
    		err = do_move_page_to_node_array(mm, pm,
    						 flags & MPOL_MF_MOVE_ALL);
    		if (err < 0)
    			goto out_pm;
    
    		/* Return status information */
    		for (j = 0; j < chunk_nr_pages; j++)
    			if (put_user(pm[j].status, status + j + chunk_start)) {
    				err = -EFAULT;
    				goto out_pm;
    			}
    	}
    	err = 0;
    
    out_pm:
    	free_page((unsigned long)pm);
    out:
    	return err;
    }
    
    /*
     * Determine the nodes of an array of pages and store it in an array of status.
     */
    static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
    				const void __user **pages, int *status)
    {
    	unsigned long i;
    
    	down_read(&mm->mmap_sem);
    
    	for (i = 0; i < nr_pages; i++) {
    		unsigned long addr = (unsigned long)(*pages);
    		struct vm_area_struct *vma;
    		struct page *page;
    		int err = -EFAULT;
    
    		vma = find_vma(mm, addr);
    		if (!vma || addr < vma->vm_start)
    			goto set_status;
    
    		/* FOLL_DUMP to ignore special (like zero) pages */
    		page = follow_page(vma, addr, FOLL_DUMP);
    
    		err = PTR_ERR(page);
    		if (IS_ERR(page))
    			goto set_status;
    
    		err = page ? page_to_nid(page) : -ENOENT;
    set_status:
    		*status = err;
    
    		pages++;
    		status++;
    	}
    
    	up_read(&mm->mmap_sem);
    }
    
    /*
     * Determine the nodes of a user array of pages and store it in
     * a user array of status.
     */
    static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
    			 const void __user * __user *pages,
    			 int __user *status)
    {
    #define DO_PAGES_STAT_CHUNK_NR 16
    	const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
    	int chunk_status[DO_PAGES_STAT_CHUNK_NR];
    
    	while (nr_pages) {
    		unsigned long chunk_nr;
    
    		chunk_nr = nr_pages;
    		if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
    			chunk_nr = DO_PAGES_STAT_CHUNK_NR;
    
    		if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
    			break;
    
    		do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
    
    		if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
    			break;
    
    		pages += chunk_nr;
    		status += chunk_nr;
    		nr_pages -= chunk_nr;
    	}
    	return nr_pages ? -EFAULT : 0;
    }
    
    /*
     * Move a list of pages in the address space of the currently executing
     * process.
     */
    SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
    		const void __user * __user *, pages,
    		const int __user *, nodes,
    		int __user *, status, int, flags)
    {
    	const struct cred *cred = current_cred(), *tcred;
    	struct task_struct *task;
    	struct mm_struct *mm;
    	int err;
    	nodemask_t task_nodes;
    
    	/* Check flags */
    	if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
    		return -EINVAL;
    
    	if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
    		return -EPERM;
    
    	/* Find the mm_struct */
    	rcu_read_lock();
    	task = pid ? find_task_by_vpid(pid) : current;
    	if (!task) {
    		rcu_read_unlock();
    		return -ESRCH;
    	}
    	get_task_struct(task);
    
    	/*
    	 * Check if this process has the right to modify the specified
    	 * process. The right exists if the process has administrative
    	 * capabilities, superuser privileges or the same
    	 * userid as the target process.
    	 */
    	tcred = __task_cred(task);
    	if (!uid_eq(cred->euid, tcred->suid) && !uid_eq(cred->euid, tcred->uid) &&
    	    !uid_eq(cred->uid,  tcred->suid) && !uid_eq(cred->uid,  tcred->uid) &&
    	    !capable(CAP_SYS_NICE)) {
    		rcu_read_unlock();
    		err = -EPERM;
    		goto out;
    	}
    	rcu_read_unlock();
    
     	err = security_task_movememory(task);
     	if (err)
    		goto out;
    
    	task_nodes = cpuset_mems_allowed(task);
    	mm = get_task_mm(task);
    	put_task_struct(task);
    
    	if (!mm)
    		return -EINVAL;
    
    	if (nodes)
    		err = do_pages_move(mm, task_nodes, nr_pages, pages,
    				    nodes, status, flags);
    	else
    		err = do_pages_stat(mm, nr_pages, pages, status);
    
    	mmput(mm);
    	return err;
    
    out:
    	put_task_struct(task);
    	return err;
    }
    
    #ifdef CONFIG_NUMA_BALANCING
    /*
     * Returns true if this is a safe migration target node for misplaced NUMA
     * pages. Currently it only checks the watermarks which crude
     */
    static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
    				   unsigned long nr_migrate_pages)
    {
    	int z;
    	for (z = pgdat->nr_zones - 1; z >= 0; z--) {
    		struct zone *zone = pgdat->node_zones + z;
    
    		if (!populated_zone(zone))
    			continue;
    
    		if (!zone_reclaimable(zone))
    			continue;
    
    		/* Avoid waking kswapd by allocating pages_to_migrate pages. */
    		if (!zone_watermark_ok(zone, 0,
    				       high_wmark_pages(zone) +
    				       nr_migrate_pages,
    				       0, 0))
    			continue;
    		return true;
    	}
    	return false;
    }
    
    static struct page *alloc_misplaced_dst_page(struct page *page,
    					   unsigned long data,
    					   int **result)
    {
    	int nid = (int) data;
    	struct page *newpage;
    
    	newpage = __alloc_pages_node(nid,
    					 (GFP_HIGHUSER_MOVABLE |
    					  __GFP_THISNODE | __GFP_NOMEMALLOC |
    					  __GFP_NORETRY | __GFP_NOWARN) &
    					 ~GFP_IOFS, 0);
    
    	return newpage;
    }
    
    /*
     * page migration rate limiting control.
     * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
     * window of time. Default here says do not migrate more than 1280M per second.
     */
    static unsigned int migrate_interval_millisecs __read_mostly = 100;
    static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
    
    /* Returns true if the node is migrate rate-limited after the update */
    static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
    					unsigned long nr_pages)
    {
    	/*
    	 * Rate-limit the amount of data that is being migrated to a node.
    	 * Optimal placement is no good if the memory bus is saturated and
    	 * all the time is being spent migrating!
    	 */
    	if (time_after(jiffies, pgdat->numabalancing_migrate_next_window)) {
    		spin_lock(&pgdat->numabalancing_migrate_lock);
    		pgdat->numabalancing_migrate_nr_pages = 0;
    		pgdat->numabalancing_migrate_next_window = jiffies +
    			msecs_to_jiffies(migrate_interval_millisecs);
    		spin_unlock(&pgdat->numabalancing_migrate_lock);
    	}
    	if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
    		trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
    								nr_pages);
    		return true;
    	}
    
    	/*
    	 * This is an unlocked non-atomic update so errors are possible.
    	 * The consequences are failing to migrate when we potentiall should
    	 * have which is not severe enough to warrant locking. If it is ever
    	 * a problem, it can be converted to a per-cpu counter.
    	 */
    	pgdat->numabalancing_migrate_nr_pages += nr_pages;
    	return false;
    }
    
    static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
    {
    	int page_lru;
    
    	VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
    
    	/* Avoid migrating to a node that is nearly full */
    	if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
    		return 0;
    
    	if (isolate_lru_page(page))
    		return 0;
    
    	/*
    	 * migrate_misplaced_transhuge_page() skips page migration's usual
    	 * check on page_count(), so we must do it here, now that the page
    	 * has been isolated: a GUP pin, or any other pin, prevents migration.
    	 * The expected page count is 3: 1 for page's mapcount and 1 for the
    	 * caller's pin and 1 for the reference taken by isolate_lru_page().
    	 */
    	if (PageTransHuge(page) && page_count(page) != 3) {
    		putback_lru_page(page);
    		return 0;
    	}
    
    	page_lru = page_is_file_cache(page);
    	mod_zone_page_state(page_zone(page), NR_ISOLATED_ANON + page_lru,
    				hpage_nr_pages(page));
    
    	/*
    	 * Isolating the page has taken another reference, so the
    	 * caller's reference can be safely dropped without the page
    	 * disappearing underneath us during migration.
    	 */
    	put_page(page);
    	return 1;
    }
    
    bool pmd_trans_migrating(pmd_t pmd)
    {
    	struct page *page = pmd_page(pmd);
    	return PageLocked(page);
    }
    
    /*
     * Attempt to migrate a misplaced page to the specified destination
     * node. Caller is expected to have an elevated reference count on
     * the page that will be dropped by this function before returning.
     */
    int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
    			   int node)
    {
    	pg_data_t *pgdat = NODE_DATA(node);
    	int isolated;
    	int nr_remaining;
    	LIST_HEAD(migratepages);
    
    	/*
    	 * Don't migrate file pages that are mapped in multiple processes
    	 * with execute permissions as they are probably shared libraries.
    	 */
    	if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
    	    (vma->vm_flags & VM_EXEC))
    		goto out;
    
    	/*
    	 * Rate-limit the amount of data that is being migrated to a node.
    	 * Optimal placement is no good if the memory bus is saturated and
    	 * all the time is being spent migrating!
    	 */
    	if (numamigrate_update_ratelimit(pgdat, 1))
    		goto out;
    
    	isolated = numamigrate_isolate_page(pgdat, page);
    	if (!isolated)
    		goto out;
    
    	list_add(&page->lru, &migratepages);
    	nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
    				     NULL, node, MIGRATE_ASYNC,
    				     MR_NUMA_MISPLACED);
    	if (nr_remaining) {
    		if (!list_empty(&migratepages)) {
    			list_del(&page->lru);
    			dec_zone_page_state(page, NR_ISOLATED_ANON +
    					page_is_file_cache(page));
    			putback_lru_page(page);
    		}
    		isolated = 0;
    	} else
    		count_vm_numa_event(NUMA_PAGE_MIGRATE);
    	BUG_ON(!list_empty(&migratepages));
    	return isolated;
    
    out:
    	put_page(page);
    	return 0;
    }
    #endif /* CONFIG_NUMA_BALANCING */
    
    #if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
    /*
     * Migrates a THP to a given target node. page must be locked and is unlocked
     * before returning.
     */
    int migrate_misplaced_transhuge_page(struct mm_struct *mm,
    				struct vm_area_struct *vma,
    				pmd_t *pmd, pmd_t entry,
    				unsigned long address,
    				struct page *page, int node)
    {
    	spinlock_t *ptl;
    	pg_data_t *pgdat = NODE_DATA(node);
    	int isolated = 0;
    	struct page *new_page = NULL;
    	int page_lru = page_is_file_cache(page);
    	unsigned long mmun_start = address & HPAGE_PMD_MASK;
    	unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
    	pmd_t orig_entry;
    
    	/*
    	 * Rate-limit the amount of data that is being migrated to a node.
    	 * Optimal placement is no good if the memory bus is saturated and
    	 * all the time is being spent migrating!
    	 */
    	if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
    		goto out_dropref;
    
    	new_page = alloc_pages_node(node,
    		(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_WAIT,
    		HPAGE_PMD_ORDER);
    	if (!new_page)
    		goto out_fail;
    
    	isolated = numamigrate_isolate_page(pgdat, page);
    	if (!isolated) {
    		put_page(new_page);
    		goto out_fail;
    	}
    
    	if (mm_tlb_flush_pending(mm))
    		flush_tlb_range(vma, mmun_start, mmun_end);
    
    	/* Prepare a page as a migration target */
    	__set_page_locked(new_page);
    	SetPageSwapBacked(new_page);
    
    	/* anon mapping, we can simply copy page->mapping to the new page: */
    	new_page->mapping = page->mapping;
    	new_page->index = page->index;
    	migrate_page_copy(new_page, page);
    	WARN_ON(PageLRU(new_page));
    
    	/* Recheck the target PMD */
    	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
    	ptl = pmd_lock(mm, pmd);
    	if (unlikely(!pmd_same(*pmd, entry) || page_count(page) != 2)) {
    fail_putback:
    		spin_unlock(ptl);
    		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
    
    		/* Reverse changes made by migrate_page_copy() */
    		if (TestClearPageActive(new_page))
    			SetPageActive(page);
    		if (TestClearPageUnevictable(new_page))
    			SetPageUnevictable(page);
    
    		unlock_page(new_page);
    		put_page(new_page);		/* Free it */
    
    		/* Retake the callers reference and putback on LRU */
    		get_page(page);
    		putback_lru_page(page);
    		mod_zone_page_state(page_zone(page),
    			 NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
    
    		goto out_unlock;
    	}
    
    	orig_entry = *pmd;
    	entry = mk_pmd(new_page, vma->vm_page_prot);
    	entry = pmd_mkhuge(entry);
    	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
    
    	/*
    	 * Clear the old entry under pagetable lock and establish the new PTE.
    	 * Any parallel GUP will either observe the old page blocking on the
    	 * page lock, block on the page table lock or observe the new page.
    	 * The SetPageUptodate on the new page and page_add_new_anon_rmap
    	 * guarantee the copy is visible before the pagetable update.
    	 */
    	flush_cache_range(vma, mmun_start, mmun_end);
    	page_add_anon_rmap(new_page, vma, mmun_start);
    	pmdp_huge_clear_flush_notify(vma, mmun_start, pmd);
    	set_pmd_at(mm, mmun_start, pmd, entry);
    	flush_tlb_range(vma, mmun_start, mmun_end);
    	update_mmu_cache_pmd(vma, address, &entry);
    
    	if (page_count(page) != 2) {
    		set_pmd_at(mm, mmun_start, pmd, orig_entry);
    		flush_tlb_range(vma, mmun_start, mmun_end);
    		mmu_notifier_invalidate_range(mm, mmun_start, mmun_end);
    		update_mmu_cache_pmd(vma, address, &entry);
    		page_remove_rmap(new_page);
    		goto fail_putback;
    	}
    
    	mlock_migrate_page(new_page, page);
    	set_page_memcg(new_page, page_memcg(page));
    	set_page_memcg(page, NULL);
    	page_remove_rmap(page);
    
    	spin_unlock(ptl);
    	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
    
    	/* Take an "isolate" reference and put new page on the LRU. */
    	get_page(new_page);
    	putback_lru_page(new_page);
    
    	unlock_page(new_page);
    	unlock_page(page);
    	put_page(page);			/* Drop the rmap reference */
    	put_page(page);			/* Drop the LRU isolation reference */
    
    	count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
    	count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
    
    	mod_zone_page_state(page_zone(page),
    			NR_ISOLATED_ANON + page_lru,
    			-HPAGE_PMD_NR);
    	return isolated;
    
    out_fail:
    	count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
    out_dropref:
    	ptl = pmd_lock(mm, pmd);
    	if (pmd_same(*pmd, entry)) {
    		entry = pmd_modify(entry, vma->vm_page_prot);
    		set_pmd_at(mm, mmun_start, pmd, entry);
    		update_mmu_cache_pmd(vma, address, &entry);
    	}
    	spin_unlock(ptl);
    
    out_unlock:
    	unlock_page(page);
    	put_page(page);
    	return 0;
    }
    #endif /* CONFIG_NUMA_BALANCING */
    
    #endif /* CONFIG_NUMA */