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32 results

rmap.c

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  • rmap.c 51.17 KiB
    /*
     * mm/rmap.c - physical to virtual reverse mappings
     *
     * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
     * Released under the General Public License (GPL).
     *
     * Simple, low overhead reverse mapping scheme.
     * Please try to keep this thing as modular as possible.
     *
     * Provides methods for unmapping each kind of mapped page:
     * the anon methods track anonymous pages, and
     * the file methods track pages belonging to an inode.
     *
     * Original design by Rik van Riel <riel@conectiva.com.br> 2001
     * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
     * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
     * Contributions by Hugh Dickins 2003, 2004
     */
    
    /*
     * Lock ordering in mm:
     *
     * inode->i_mutex	(while writing or truncating, not reading or faulting)
     *   mm->mmap_sem
     *     page->flags PG_locked (lock_page)
     *       hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share)
     *         mapping->i_mmap_rwsem
     *           anon_vma->rwsem
     *             mm->page_table_lock or pte_lock
     *               zone_lru_lock (in mark_page_accessed, isolate_lru_page)
     *               swap_lock (in swap_duplicate, swap_info_get)
     *                 mmlist_lock (in mmput, drain_mmlist and others)
     *                 mapping->private_lock (in __set_page_dirty_buffers)
     *                   mem_cgroup_{begin,end}_page_stat (memcg->move_lock)
     *                     mapping->tree_lock (widely used)
     *                 inode->i_lock (in set_page_dirty's __mark_inode_dirty)
     *                 bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
     *                   sb_lock (within inode_lock in fs/fs-writeback.c)
     *                   mapping->tree_lock (widely used, in set_page_dirty,
     *                             in arch-dependent flush_dcache_mmap_lock,
     *                             within bdi.wb->list_lock in __sync_single_inode)
     *
     * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
     *   ->tasklist_lock
     *     pte map lock
     */
    
    #include <linux/mm.h>
    #include <linux/pagemap.h>
    #include <linux/swap.h>
    #include <linux/swapops.h>
    #include <linux/slab.h>
    #include <linux/init.h>
    #include <linux/ksm.h>
    #include <linux/rmap.h>
    #include <linux/rcupdate.h>
    #include <linux/export.h>
    #include <linux/memcontrol.h>
    #include <linux/mmu_notifier.h>
    #include <linux/migrate.h>
    #include <linux/hugetlb.h>
    #include <linux/backing-dev.h>
    #include <linux/page_idle.h>
    
    #include <asm/tlbflush.h>
    
    #include <trace/events/tlb.h>
    
    #include "internal.h"
    
    static struct kmem_cache *anon_vma_cachep;
    static struct kmem_cache *anon_vma_chain_cachep;
    
    static inline struct anon_vma *anon_vma_alloc(void)
    {
    	struct anon_vma *anon_vma;
    
    	anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
    	if (anon_vma) {
    		atomic_set(&anon_vma->refcount, 1);
    		anon_vma->degree = 1;	/* Reference for first vma */
    		anon_vma->parent = anon_vma;
    		/*
    		 * Initialise the anon_vma root to point to itself. If called
    		 * from fork, the root will be reset to the parents anon_vma.
    		 */
    		anon_vma->root = anon_vma;
    	}
    
    	return anon_vma;
    }
    
    static inline void anon_vma_free(struct anon_vma *anon_vma)
    {
    	VM_BUG_ON(atomic_read(&anon_vma->refcount));
    
    	/*
    	 * Synchronize against page_lock_anon_vma_read() such that
    	 * we can safely hold the lock without the anon_vma getting
    	 * freed.
    	 *
    	 * Relies on the full mb implied by the atomic_dec_and_test() from
    	 * put_anon_vma() against the acquire barrier implied by
    	 * down_read_trylock() from page_lock_anon_vma_read(). This orders:
    	 *
    	 * page_lock_anon_vma_read()	VS	put_anon_vma()
    	 *   down_read_trylock()		  atomic_dec_and_test()
    	 *   LOCK				  MB
    	 *   atomic_read()			  rwsem_is_locked()
    	 *
    	 * LOCK should suffice since the actual taking of the lock must
    	 * happen _before_ what follows.
    	 */
    	might_sleep();
    	if (rwsem_is_locked(&anon_vma->root->rwsem)) {
    		anon_vma_lock_write(anon_vma);
    		anon_vma_unlock_write(anon_vma);
    	}
    
    	kmem_cache_free(anon_vma_cachep, anon_vma);
    }
    
    static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
    {
    	return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
    }
    
    static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
    {
    	kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
    }
    
    static void anon_vma_chain_link(struct vm_area_struct *vma,
    				struct anon_vma_chain *avc,
    				struct anon_vma *anon_vma)
    {
    	avc->vma = vma;
    	avc->anon_vma = anon_vma;
    	list_add(&avc->same_vma, &vma->anon_vma_chain);
    	anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
    }
    
    /**
     * anon_vma_prepare - attach an anon_vma to a memory region
     * @vma: the memory region in question
     *
     * This makes sure the memory mapping described by 'vma' has
     * an 'anon_vma' attached to it, so that we can associate the
     * anonymous pages mapped into it with that anon_vma.
     *
     * The common case will be that we already have one, but if
     * not we either need to find an adjacent mapping that we
     * can re-use the anon_vma from (very common when the only
     * reason for splitting a vma has been mprotect()), or we
     * allocate a new one.
     *
     * Anon-vma allocations are very subtle, because we may have
     * optimistically looked up an anon_vma in page_lock_anon_vma_read()
     * and that may actually touch the spinlock even in the newly
     * allocated vma (it depends on RCU to make sure that the
     * anon_vma isn't actually destroyed).
     *
     * As a result, we need to do proper anon_vma locking even
     * for the new allocation. At the same time, we do not want
     * to do any locking for the common case of already having
     * an anon_vma.
     *
     * This must be called with the mmap_sem held for reading.
     */
    int anon_vma_prepare(struct vm_area_struct *vma)
    {
    	struct anon_vma *anon_vma = vma->anon_vma;
    	struct anon_vma_chain *avc;
    
    	might_sleep();
    	if (unlikely(!anon_vma)) {
    		struct mm_struct *mm = vma->vm_mm;
    		struct anon_vma *allocated;
    
    		avc = anon_vma_chain_alloc(GFP_KERNEL);
    		if (!avc)
    			goto out_enomem;
    
    		anon_vma = find_mergeable_anon_vma(vma);
    		allocated = NULL;
    		if (!anon_vma) {
    			anon_vma = anon_vma_alloc();
    			if (unlikely(!anon_vma))
    				goto out_enomem_free_avc;
    			allocated = anon_vma;
    		}
    
    		anon_vma_lock_write(anon_vma);
    		/* page_table_lock to protect against threads */
    		spin_lock(&mm->page_table_lock);
    		if (likely(!vma->anon_vma)) {
    			vma->anon_vma = anon_vma;
    			anon_vma_chain_link(vma, avc, anon_vma);
    			/* vma reference or self-parent link for new root */
    			anon_vma->degree++;
    			allocated = NULL;
    			avc = NULL;
    		}
    		spin_unlock(&mm->page_table_lock);
    		anon_vma_unlock_write(anon_vma);
    
    		if (unlikely(allocated))
    			put_anon_vma(allocated);
    		if (unlikely(avc))
    			anon_vma_chain_free(avc);
    	}
    	return 0;
    
     out_enomem_free_avc:
    	anon_vma_chain_free(avc);
     out_enomem:
    	return -ENOMEM;
    }
    
    /*
     * This is a useful helper function for locking the anon_vma root as
     * we traverse the vma->anon_vma_chain, looping over anon_vma's that
     * have the same vma.
     *
     * Such anon_vma's should have the same root, so you'd expect to see
     * just a single mutex_lock for the whole traversal.
     */
    static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
    {
    	struct anon_vma *new_root = anon_vma->root;
    	if (new_root != root) {
    		if (WARN_ON_ONCE(root))
    			up_write(&root->rwsem);
    		root = new_root;
    		down_write(&root->rwsem);
    	}
    	return root;
    }
    
    static inline void unlock_anon_vma_root(struct anon_vma *root)
    {
    	if (root)
    		up_write(&root->rwsem);
    }
    
    /*
     * Attach the anon_vmas from src to dst.
     * Returns 0 on success, -ENOMEM on failure.
     *
     * If dst->anon_vma is NULL this function tries to find and reuse existing
     * anon_vma which has no vmas and only one child anon_vma. This prevents
     * degradation of anon_vma hierarchy to endless linear chain in case of
     * constantly forking task. On the other hand, an anon_vma with more than one
     * child isn't reused even if there was no alive vma, thus rmap walker has a
     * good chance of avoiding scanning the whole hierarchy when it searches where
     * page is mapped.
     */
    int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
    {
    	struct anon_vma_chain *avc, *pavc;
    	struct anon_vma *root = NULL;
    
    	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
    		struct anon_vma *anon_vma;
    
    		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
    		if (unlikely(!avc)) {
    			unlock_anon_vma_root(root);
    			root = NULL;
    			avc = anon_vma_chain_alloc(GFP_KERNEL);
    			if (!avc)
    				goto enomem_failure;
    		}
    		anon_vma = pavc->anon_vma;
    		root = lock_anon_vma_root(root, anon_vma);
    		anon_vma_chain_link(dst, avc, anon_vma);
    
    		/*
    		 * Reuse existing anon_vma if its degree lower than two,
    		 * that means it has no vma and only one anon_vma child.
    		 *
    		 * Do not chose parent anon_vma, otherwise first child
    		 * will always reuse it. Root anon_vma is never reused:
    		 * it has self-parent reference and at least one child.
    		 */
    		if (!dst->anon_vma && anon_vma != src->anon_vma &&
    				anon_vma->degree < 2)
    			dst->anon_vma = anon_vma;
    	}
    	if (dst->anon_vma)
    		dst->anon_vma->degree++;
    	unlock_anon_vma_root(root);
    	return 0;
    
     enomem_failure:
    	/*
    	 * dst->anon_vma is dropped here otherwise its degree can be incorrectly
    	 * decremented in unlink_anon_vmas().
    	 * We can safely do this because callers of anon_vma_clone() don't care
    	 * about dst->anon_vma if anon_vma_clone() failed.
    	 */
    	dst->anon_vma = NULL;
    	unlink_anon_vmas(dst);
    	return -ENOMEM;
    }
    
    /*
     * Attach vma to its own anon_vma, as well as to the anon_vmas that
     * the corresponding VMA in the parent process is attached to.
     * Returns 0 on success, non-zero on failure.
     */
    int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
    {
    	struct anon_vma_chain *avc;
    	struct anon_vma *anon_vma;
    	int error;
    
    	/* Don't bother if the parent process has no anon_vma here. */
    	if (!pvma->anon_vma)
    		return 0;
    
    	/* Drop inherited anon_vma, we'll reuse existing or allocate new. */
    	vma->anon_vma = NULL;
    
    	/*
    	 * First, attach the new VMA to the parent VMA's anon_vmas,
    	 * so rmap can find non-COWed pages in child processes.
    	 */
    	error = anon_vma_clone(vma, pvma);
    	if (error)
    		return error;
    
    	/* An existing anon_vma has been reused, all done then. */
    	if (vma->anon_vma)
    		return 0;
    
    	/* Then add our own anon_vma. */
    	anon_vma = anon_vma_alloc();
    	if (!anon_vma)
    		goto out_error;
    	avc = anon_vma_chain_alloc(GFP_KERNEL);
    	if (!avc)
    		goto out_error_free_anon_vma;
    
    	/*
    	 * The root anon_vma's spinlock is the lock actually used when we
    	 * lock any of the anon_vmas in this anon_vma tree.
    	 */
    	anon_vma->root = pvma->anon_vma->root;
    	anon_vma->parent = pvma->anon_vma;
    	/*
    	 * With refcounts, an anon_vma can stay around longer than the
    	 * process it belongs to. The root anon_vma needs to be pinned until
    	 * this anon_vma is freed, because the lock lives in the root.
    	 */
    	get_anon_vma(anon_vma->root);
    	/* Mark this anon_vma as the one where our new (COWed) pages go. */
    	vma->anon_vma = anon_vma;
    	anon_vma_lock_write(anon_vma);
    	anon_vma_chain_link(vma, avc, anon_vma);
    	anon_vma->parent->degree++;
    	anon_vma_unlock_write(anon_vma);
    
    	return 0;
    
     out_error_free_anon_vma:
    	put_anon_vma(anon_vma);
     out_error:
    	unlink_anon_vmas(vma);
    	return -ENOMEM;
    }
    
    void unlink_anon_vmas(struct vm_area_struct *vma)
    {
    	struct anon_vma_chain *avc, *next;
    	struct anon_vma *root = NULL;
    
    	/*
    	 * Unlink each anon_vma chained to the VMA.  This list is ordered
    	 * from newest to oldest, ensuring the root anon_vma gets freed last.
    	 */
    	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
    		struct anon_vma *anon_vma = avc->anon_vma;
    
    		root = lock_anon_vma_root(root, anon_vma);
    		anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);
    
    		/*
    		 * Leave empty anon_vmas on the list - we'll need
    		 * to free them outside the lock.
    		 */
    		if (RB_EMPTY_ROOT(&anon_vma->rb_root)) {
    			anon_vma->parent->degree--;
    			continue;
    		}
    
    		list_del(&avc->same_vma);
    		anon_vma_chain_free(avc);
    	}
    	if (vma->anon_vma)
    		vma->anon_vma->degree--;
    	unlock_anon_vma_root(root);
    
    	/*
    	 * Iterate the list once more, it now only contains empty and unlinked
    	 * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
    	 * needing to write-acquire the anon_vma->root->rwsem.
    	 */
    	list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
    		struct anon_vma *anon_vma = avc->anon_vma;
    
    		VM_WARN_ON(anon_vma->degree);
    		put_anon_vma(anon_vma);
    
    		list_del(&avc->same_vma);
    		anon_vma_chain_free(avc);
    	}
    }
    
    static void anon_vma_ctor(void *data)
    {
    	struct anon_vma *anon_vma = data;
    
    	init_rwsem(&anon_vma->rwsem);
    	atomic_set(&anon_vma->refcount, 0);
    	anon_vma->rb_root = RB_ROOT;
    }
    
    void __init anon_vma_init(void)
    {
    	anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
    			0, SLAB_DESTROY_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
    			anon_vma_ctor);
    	anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
    			SLAB_PANIC|SLAB_ACCOUNT);
    }
    
    /*
     * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
     *
     * Since there is no serialization what so ever against page_remove_rmap()
     * the best this function can do is return a locked anon_vma that might
     * have been relevant to this page.
     *
     * The page might have been remapped to a different anon_vma or the anon_vma
     * returned may already be freed (and even reused).
     *
     * In case it was remapped to a different anon_vma, the new anon_vma will be a
     * child of the old anon_vma, and the anon_vma lifetime rules will therefore
     * ensure that any anon_vma obtained from the page will still be valid for as
     * long as we observe page_mapped() [ hence all those page_mapped() tests ].
     *
     * All users of this function must be very careful when walking the anon_vma
     * chain and verify that the page in question is indeed mapped in it
     * [ something equivalent to page_mapped_in_vma() ].
     *
     * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
     * that the anon_vma pointer from page->mapping is valid if there is a
     * mapcount, we can dereference the anon_vma after observing those.
     */
    struct anon_vma *page_get_anon_vma(struct page *page)
    {
    	struct anon_vma *anon_vma = NULL;
    	unsigned long anon_mapping;
    
    	rcu_read_lock();
    	anon_mapping = (unsigned long)READ_ONCE(page->mapping);
    	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
    		goto out;
    	if (!page_mapped(page))
    		goto out;
    
    	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
    	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
    		anon_vma = NULL;
    		goto out;
    	}
    
    	/*
    	 * If this page is still mapped, then its anon_vma cannot have been
    	 * freed.  But if it has been unmapped, we have no security against the
    	 * anon_vma structure being freed and reused (for another anon_vma:
    	 * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
    	 * above cannot corrupt).
    	 */
    	if (!page_mapped(page)) {
    		rcu_read_unlock();
    		put_anon_vma(anon_vma);
    		return NULL;
    	}
    out:
    	rcu_read_unlock();
    
    	return anon_vma;
    }
    
    /*
     * Similar to page_get_anon_vma() except it locks the anon_vma.
     *
     * Its a little more complex as it tries to keep the fast path to a single
     * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
     * reference like with page_get_anon_vma() and then block on the mutex.
     */
    struct anon_vma *page_lock_anon_vma_read(struct page *page)
    {
    	struct anon_vma *anon_vma = NULL;
    	struct anon_vma *root_anon_vma;
    	unsigned long anon_mapping;
    
    	rcu_read_lock();
    	anon_mapping = (unsigned long)READ_ONCE(page->mapping);
    	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
    		goto out;
    	if (!page_mapped(page))
    		goto out;
    
    	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
    	root_anon_vma = READ_ONCE(anon_vma->root);
    	if (down_read_trylock(&root_anon_vma->rwsem)) {
    		/*
    		 * If the page is still mapped, then this anon_vma is still
    		 * its anon_vma, and holding the mutex ensures that it will
    		 * not go away, see anon_vma_free().
    		 */
    		if (!page_mapped(page)) {
    			up_read(&root_anon_vma->rwsem);
    			anon_vma = NULL;
    		}
    		goto out;
    	}
    
    	/* trylock failed, we got to sleep */
    	if (!atomic_inc_not_zero(&anon_vma->refcount)) {
    		anon_vma = NULL;
    		goto out;
    	}
    
    	if (!page_mapped(page)) {
    		rcu_read_unlock();
    		put_anon_vma(anon_vma);
    		return NULL;
    	}
    
    	/* we pinned the anon_vma, its safe to sleep */
    	rcu_read_unlock();
    	anon_vma_lock_read(anon_vma);
    
    	if (atomic_dec_and_test(&anon_vma->refcount)) {
    		/*
    		 * Oops, we held the last refcount, release the lock
    		 * and bail -- can't simply use put_anon_vma() because
    		 * we'll deadlock on the anon_vma_lock_write() recursion.
    		 */
    		anon_vma_unlock_read(anon_vma);
    		__put_anon_vma(anon_vma);
    		anon_vma = NULL;
    	}
    
    	return anon_vma;
    
    out:
    	rcu_read_unlock();
    	return anon_vma;
    }
    
    void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
    {
    	anon_vma_unlock_read(anon_vma);
    }
    
    #ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
    /*
     * Flush TLB entries for recently unmapped pages from remote CPUs. It is
     * important if a PTE was dirty when it was unmapped that it's flushed
     * before any IO is initiated on the page to prevent lost writes. Similarly,
     * it must be flushed before freeing to prevent data leakage.
     */
    void try_to_unmap_flush(void)
    {
    	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
    	int cpu;
    
    	if (!tlb_ubc->flush_required)
    		return;
    
    	cpu = get_cpu();
    
    	if (cpumask_test_cpu(cpu, &tlb_ubc->cpumask)) {
    		count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
    		local_flush_tlb();
    		trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
    	}
    
    	if (cpumask_any_but(&tlb_ubc->cpumask, cpu) < nr_cpu_ids)
    		flush_tlb_others(&tlb_ubc->cpumask, NULL, 0, TLB_FLUSH_ALL);
    	cpumask_clear(&tlb_ubc->cpumask);
    	tlb_ubc->flush_required = false;
    	tlb_ubc->writable = false;
    	put_cpu();
    }
    
    /* Flush iff there are potentially writable TLB entries that can race with IO */
    void try_to_unmap_flush_dirty(void)
    {
    	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
    
    	if (tlb_ubc->writable)
    		try_to_unmap_flush();
    }
    
    static void set_tlb_ubc_flush_pending(struct mm_struct *mm,
    		struct page *page, bool writable)
    {
    	struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
    
    	cpumask_or(&tlb_ubc->cpumask, &tlb_ubc->cpumask, mm_cpumask(mm));
    	tlb_ubc->flush_required = true;
    
    	/*
    	 * If the PTE was dirty then it's best to assume it's writable. The
    	 * caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
    	 * before the page is queued for IO.
    	 */
    	if (writable)
    		tlb_ubc->writable = true;
    }
    
    /*
     * Returns true if the TLB flush should be deferred to the end of a batch of
     * unmap operations to reduce IPIs.
     */
    static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
    {
    	bool should_defer = false;
    
    	if (!(flags & TTU_BATCH_FLUSH))
    		return false;
    
    	/* If remote CPUs need to be flushed then defer batch the flush */
    	if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
    		should_defer = true;
    	put_cpu();
    
    	return should_defer;
    }
    #else
    static void set_tlb_ubc_flush_pending(struct mm_struct *mm,
    		struct page *page, bool writable)
    {
    }
    
    static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
    {
    	return false;
    }
    #endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */
    
    /*
     * At what user virtual address is page expected in vma?
     * Caller should check the page is actually part of the vma.
     */
    unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
    {
    	unsigned long address;
    	if (PageAnon(page)) {
    		struct anon_vma *page__anon_vma = page_anon_vma(page);
    		/*
    		 * Note: swapoff's unuse_vma() is more efficient with this
    		 * check, and needs it to match anon_vma when KSM is active.
    		 */
    		if (!vma->anon_vma || !page__anon_vma ||
    		    vma->anon_vma->root != page__anon_vma->root)
    			return -EFAULT;
    	} else if (page->mapping) {
    		if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping)
    			return -EFAULT;
    	} else
    		return -EFAULT;
    	address = __vma_address(page, vma);
    	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
    		return -EFAULT;
    	return address;
    }
    
    pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
    {
    	pgd_t *pgd;
    	pud_t *pud;
    	pmd_t *pmd = NULL;
    	pmd_t pmde;
    
    	pgd = pgd_offset(mm, address);
    	if (!pgd_present(*pgd))
    		goto out;
    
    	pud = pud_offset(pgd, address);
    	if (!pud_present(*pud))
    		goto out;
    
    	pmd = pmd_offset(pud, address);
    	/*
    	 * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
    	 * without holding anon_vma lock for write.  So when looking for a
    	 * genuine pmde (in which to find pte), test present and !THP together.
    	 */
    	pmde = *pmd;
    	barrier();
    	if (!pmd_present(pmde) || pmd_trans_huge(pmde))
    		pmd = NULL;
    out:
    	return pmd;
    }
    
    /*
     * Check that @page is mapped at @address into @mm.
     *
     * If @sync is false, page_check_address may perform a racy check to avoid
     * the page table lock when the pte is not present (helpful when reclaiming
     * highly shared pages).
     *
     * On success returns with pte mapped and locked.
     */
    pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
    			  unsigned long address, spinlock_t **ptlp, int sync)
    {
    	pmd_t *pmd;
    	pte_t *pte;
    	spinlock_t *ptl;
    
    	if (unlikely(PageHuge(page))) {
    		/* when pud is not present, pte will be NULL */
    		pte = huge_pte_offset(mm, address);
    		if (!pte)
    			return NULL;
    
    		ptl = huge_pte_lockptr(page_hstate(page), mm, pte);
    		goto check;
    	}
    
    	pmd = mm_find_pmd(mm, address);
    	if (!pmd)
    		return NULL;
    
    	pte = pte_offset_map(pmd, address);
    	/* Make a quick check before getting the lock */
    	if (!sync && !pte_present(*pte)) {
    		pte_unmap(pte);
    		return NULL;
    	}
    
    	ptl = pte_lockptr(mm, pmd);
    check:
    	spin_lock(ptl);
    	if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
    		*ptlp = ptl;
    		return pte;
    	}
    	pte_unmap_unlock(pte, ptl);
    	return NULL;
    }
    
    /**
     * page_mapped_in_vma - check whether a page is really mapped in a VMA
     * @page: the page to test
     * @vma: the VMA to test
     *
     * Returns 1 if the page is mapped into the page tables of the VMA, 0
     * if the page is not mapped into the page tables of this VMA.  Only
     * valid for normal file or anonymous VMAs.
     */
    int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
    {
    	unsigned long address;
    	pte_t *pte;
    	spinlock_t *ptl;
    
    	address = __vma_address(page, vma);
    	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
    		return 0;
    	pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
    	if (!pte)			/* the page is not in this mm */
    		return 0;
    	pte_unmap_unlock(pte, ptl);
    
    	return 1;
    }
    
    #ifdef CONFIG_TRANSPARENT_HUGEPAGE
    /*
     * Check that @page is mapped at @address into @mm. In contrast to
     * page_check_address(), this function can handle transparent huge pages.
     *
     * On success returns true with pte mapped and locked. For PMD-mapped
     * transparent huge pages *@ptep is set to NULL.
     */
    bool page_check_address_transhuge(struct page *page, struct mm_struct *mm,
    				  unsigned long address, pmd_t **pmdp,
    				  pte_t **ptep, spinlock_t **ptlp)
    {
    	pgd_t *pgd;
    	pud_t *pud;
    	pmd_t *pmd;
    	pte_t *pte;
    	spinlock_t *ptl;
    
    	if (unlikely(PageHuge(page))) {
    		/* when pud is not present, pte will be NULL */
    		pte = huge_pte_offset(mm, address);
    		if (!pte)
    			return false;
    
    		ptl = huge_pte_lockptr(page_hstate(page), mm, pte);
    		pmd = NULL;
    		goto check_pte;
    	}
    
    	pgd = pgd_offset(mm, address);
    	if (!pgd_present(*pgd))
    		return false;
    	pud = pud_offset(pgd, address);
    	if (!pud_present(*pud))
    		return false;
    	pmd = pmd_offset(pud, address);
    
    	if (pmd_trans_huge(*pmd)) {
    		ptl = pmd_lock(mm, pmd);
    		if (!pmd_present(*pmd))
    			goto unlock_pmd;
    		if (unlikely(!pmd_trans_huge(*pmd))) {
    			spin_unlock(ptl);
    			goto map_pte;
    		}
    
    		if (pmd_page(*pmd) != page)
    			goto unlock_pmd;
    
    		pte = NULL;
    		goto found;
    unlock_pmd:
    		spin_unlock(ptl);
    		return false;
    	} else {
    		pmd_t pmde = *pmd;
    
    		barrier();
    		if (!pmd_present(pmde) || pmd_trans_huge(pmde))
    			return false;
    	}
    map_pte:
    	pte = pte_offset_map(pmd, address);
    	if (!pte_present(*pte)) {
    		pte_unmap(pte);
    		return false;
    	}
    
    	ptl = pte_lockptr(mm, pmd);
    check_pte:
    	spin_lock(ptl);
    
    	if (!pte_present(*pte)) {
    		pte_unmap_unlock(pte, ptl);
    		return false;
    	}
    
    	/* THP can be referenced by any subpage */
    	if (pte_pfn(*pte) - page_to_pfn(page) >= hpage_nr_pages(page)) {
    		pte_unmap_unlock(pte, ptl);
    		return false;
    	}
    found:
    	*ptep = pte;
    	*pmdp = pmd;
    	*ptlp = ptl;
    	return true;
    }
    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
    
    struct page_referenced_arg {
    	int mapcount;
    	int referenced;
    	unsigned long vm_flags;
    	struct mem_cgroup *memcg;
    };
    /*
     * arg: page_referenced_arg will be passed
     */
    static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
    			unsigned long address, void *arg)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	struct page_referenced_arg *pra = arg;
    	pmd_t *pmd;
    	pte_t *pte;
    	spinlock_t *ptl;
    	int referenced = 0;
    
    	if (!page_check_address_transhuge(page, mm, address, &pmd, &pte, &ptl))
    		return SWAP_AGAIN;
    
    	if (vma->vm_flags & VM_LOCKED) {
    		if (pte)
    			pte_unmap(pte);
    		spin_unlock(ptl);
    		pra->vm_flags |= VM_LOCKED;
    		return SWAP_FAIL; /* To break the loop */
    	}
    
    	if (pte) {
    		if (ptep_clear_flush_young_notify(vma, address, pte)) {
    			/*
    			 * Don't treat a reference through a sequentially read
    			 * mapping as such.  If the page has been used in
    			 * another mapping, we will catch it; if this other
    			 * mapping is already gone, the unmap path will have
    			 * set PG_referenced or activated the page.
    			 */
    			if (likely(!(vma->vm_flags & VM_SEQ_READ)))
    				referenced++;
    		}
    		pte_unmap(pte);
    	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
    		if (pmdp_clear_flush_young_notify(vma, address, pmd))
    			referenced++;
    	} else {
    		/* unexpected pmd-mapped page? */
    		WARN_ON_ONCE(1);
    	}
    	spin_unlock(ptl);
    
    	if (referenced)
    		clear_page_idle(page);
    	if (test_and_clear_page_young(page))
    		referenced++;
    
    	if (referenced) {
    		pra->referenced++;
    		pra->vm_flags |= vma->vm_flags;
    	}
    
    	pra->mapcount--;
    	if (!pra->mapcount)
    		return SWAP_SUCCESS; /* To break the loop */
    
    	return SWAP_AGAIN;
    }
    
    static bool invalid_page_referenced_vma(struct vm_area_struct *vma, void *arg)
    {
    	struct page_referenced_arg *pra = arg;
    	struct mem_cgroup *memcg = pra->memcg;
    
    	if (!mm_match_cgroup(vma->vm_mm, memcg))
    		return true;
    
    	return false;
    }
    
    /**
     * page_referenced - test if the page was referenced
     * @page: the page to test
     * @is_locked: caller holds lock on the page
     * @memcg: target memory cgroup
     * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
     *
     * Quick test_and_clear_referenced for all mappings to a page,
     * returns the number of ptes which referenced the page.
     */
    int page_referenced(struct page *page,
    		    int is_locked,
    		    struct mem_cgroup *memcg,
    		    unsigned long *vm_flags)
    {
    	int ret;
    	int we_locked = 0;
    	struct page_referenced_arg pra = {
    		.mapcount = total_mapcount(page),
    		.memcg = memcg,
    	};
    	struct rmap_walk_control rwc = {
    		.rmap_one = page_referenced_one,
    		.arg = (void *)&pra,
    		.anon_lock = page_lock_anon_vma_read,
    	};
    
    	*vm_flags = 0;
    	if (!page_mapped(page))
    		return 0;
    
    	if (!page_rmapping(page))
    		return 0;
    
    	if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
    		we_locked = trylock_page(page);
    		if (!we_locked)
    			return 1;
    	}
    
    	/*
    	 * If we are reclaiming on behalf of a cgroup, skip
    	 * counting on behalf of references from different
    	 * cgroups
    	 */
    	if (memcg) {
    		rwc.invalid_vma = invalid_page_referenced_vma;
    	}
    
    	ret = rmap_walk(page, &rwc);
    	*vm_flags = pra.vm_flags;
    
    	if (we_locked)
    		unlock_page(page);
    
    	return pra.referenced;
    }
    
    static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
    			    unsigned long address, void *arg)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	pte_t *pte;
    	spinlock_t *ptl;
    	int ret = 0;
    	int *cleaned = arg;
    
    	pte = page_check_address(page, mm, address, &ptl, 1);
    	if (!pte)
    		goto out;
    
    	if (pte_dirty(*pte) || pte_write(*pte)) {
    		pte_t entry;
    
    		flush_cache_page(vma, address, pte_pfn(*pte));
    		entry = ptep_clear_flush(vma, address, pte);
    		entry = pte_wrprotect(entry);
    		entry = pte_mkclean(entry);
    		set_pte_at(mm, address, pte, entry);
    		ret = 1;
    	}
    
    	pte_unmap_unlock(pte, ptl);
    
    	if (ret) {
    		mmu_notifier_invalidate_page(mm, address);
    		(*cleaned)++;
    	}
    out:
    	return SWAP_AGAIN;
    }
    
    static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg)
    {
    	if (vma->vm_flags & VM_SHARED)
    		return false;
    
    	return true;
    }
    
    int page_mkclean(struct page *page)
    {
    	int cleaned = 0;
    	struct address_space *mapping;
    	struct rmap_walk_control rwc = {
    		.arg = (void *)&cleaned,
    		.rmap_one = page_mkclean_one,
    		.invalid_vma = invalid_mkclean_vma,
    	};
    
    	BUG_ON(!PageLocked(page));
    
    	if (!page_mapped(page))
    		return 0;
    
    	mapping = page_mapping(page);
    	if (!mapping)
    		return 0;
    
    	rmap_walk(page, &rwc);
    
    	return cleaned;
    }
    EXPORT_SYMBOL_GPL(page_mkclean);
    
    /**
     * page_move_anon_rmap - move a page to our anon_vma
     * @page:	the page to move to our anon_vma
     * @vma:	the vma the page belongs to
     *
     * When a page belongs exclusively to one process after a COW event,
     * that page can be moved into the anon_vma that belongs to just that
     * process, so the rmap code will not search the parent or sibling
     * processes.
     */
    void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
    {
    	struct anon_vma *anon_vma = vma->anon_vma;
    
    	page = compound_head(page);
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_VMA(!anon_vma, vma);
    
    	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
    	/*
    	 * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
    	 * simultaneously, so a concurrent reader (eg page_referenced()'s
    	 * PageAnon()) will not see one without the other.
    	 */
    	WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
    }
    
    /**
     * __page_set_anon_rmap - set up new anonymous rmap
     * @page:	Page to add to rmap	
     * @vma:	VM area to add page to.
     * @address:	User virtual address of the mapping	
     * @exclusive:	the page is exclusively owned by the current process
     */
    static void __page_set_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address, int exclusive)
    {
    	struct anon_vma *anon_vma = vma->anon_vma;
    
    	BUG_ON(!anon_vma);
    
    	if (PageAnon(page))
    		return;
    
    	/*
    	 * If the page isn't exclusively mapped into this vma,
    	 * we must use the _oldest_ possible anon_vma for the
    	 * page mapping!
    	 */
    	if (!exclusive)
    		anon_vma = anon_vma->root;
    
    	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
    	page->mapping = (struct address_space *) anon_vma;
    	page->index = linear_page_index(vma, address);
    }
    
    /**
     * __page_check_anon_rmap - sanity check anonymous rmap addition
     * @page:	the page to add the mapping to
     * @vma:	the vm area in which the mapping is added
     * @address:	the user virtual address mapped
     */
    static void __page_check_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address)
    {
    #ifdef CONFIG_DEBUG_VM
    	/*
    	 * The page's anon-rmap details (mapping and index) are guaranteed to
    	 * be set up correctly at this point.
    	 *
    	 * We have exclusion against page_add_anon_rmap because the caller
    	 * always holds the page locked, except if called from page_dup_rmap,
    	 * in which case the page is already known to be setup.
    	 *
    	 * We have exclusion against page_add_new_anon_rmap because those pages
    	 * are initially only visible via the pagetables, and the pte is locked
    	 * over the call to page_add_new_anon_rmap.
    	 */
    	BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
    	BUG_ON(page_to_pgoff(page) != linear_page_index(vma, address));
    #endif
    }
    
    /**
     * page_add_anon_rmap - add pte mapping to an anonymous page
     * @page:	the page to add the mapping to
     * @vma:	the vm area in which the mapping is added
     * @address:	the user virtual address mapped
     * @compound:	charge the page as compound or small page
     *
     * The caller needs to hold the pte lock, and the page must be locked in
     * the anon_vma case: to serialize mapping,index checking after setting,
     * and to ensure that PageAnon is not being upgraded racily to PageKsm
     * (but PageKsm is never downgraded to PageAnon).
     */
    void page_add_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address, bool compound)
    {
    	do_page_add_anon_rmap(page, vma, address, compound ? RMAP_COMPOUND : 0);
    }
    
    /*
     * Special version of the above for do_swap_page, which often runs
     * into pages that are exclusively owned by the current process.
     * Everybody else should continue to use page_add_anon_rmap above.
     */
    void do_page_add_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address, int flags)
    {
    	bool compound = flags & RMAP_COMPOUND;
    	bool first;
    
    	if (compound) {
    		atomic_t *mapcount;
    		VM_BUG_ON_PAGE(!PageLocked(page), page);
    		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
    		mapcount = compound_mapcount_ptr(page);
    		first = atomic_inc_and_test(mapcount);
    	} else {
    		first = atomic_inc_and_test(&page->_mapcount);
    	}
    
    	if (first) {
    		int nr = compound ? hpage_nr_pages(page) : 1;
    		/*
    		 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
    		 * these counters are not modified in interrupt context, and
    		 * pte lock(a spinlock) is held, which implies preemption
    		 * disabled.
    		 */
    		if (compound)
    			__inc_zone_page_state(page, NR_ANON_THPS);
    		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);
    	}
    	if (unlikely(PageKsm(page)))
    		return;
    
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    
    	/* address might be in next vma when migration races vma_adjust */
    	if (first)
    		__page_set_anon_rmap(page, vma, address,
    				flags & RMAP_EXCLUSIVE);
    	else
    		__page_check_anon_rmap(page, vma, address);
    }
    
    /**
     * page_add_new_anon_rmap - add pte mapping to a new anonymous page
     * @page:	the page to add the mapping to
     * @vma:	the vm area in which the mapping is added
     * @address:	the user virtual address mapped
     * @compound:	charge the page as compound or small page
     *
     * Same as page_add_anon_rmap but must only be called on *new* pages.
     * This means the inc-and-test can be bypassed.
     * Page does not have to be locked.
     */
    void page_add_new_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address, bool compound)
    {
    	int nr = compound ? hpage_nr_pages(page) : 1;
    
    	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
    	__SetPageSwapBacked(page);
    	if (compound) {
    		VM_BUG_ON_PAGE(!PageTransHuge(page), page);
    		/* increment count (starts at -1) */
    		atomic_set(compound_mapcount_ptr(page), 0);
    		__inc_zone_page_state(page, NR_ANON_THPS);
    	} else {
    		/* Anon THP always mapped first with PMD */
    		VM_BUG_ON_PAGE(PageTransCompound(page), page);
    		/* increment count (starts at -1) */
    		atomic_set(&page->_mapcount, 0);
    	}
    	__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, nr);
    	__page_set_anon_rmap(page, vma, address, 1);
    }
    
    /**
     * page_add_file_rmap - add pte mapping to a file page
     * @page: the page to add the mapping to
     *
     * The caller needs to hold the pte lock.
     */
    void page_add_file_rmap(struct page *page, bool compound)
    {
    	int i, nr = 1;
    
    	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
    	lock_page_memcg(page);
    	if (compound && PageTransHuge(page)) {
    		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
    			if (atomic_inc_and_test(&page[i]._mapcount))
    				nr++;
    		}
    		if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
    			goto out;
    		VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
    		__inc_zone_page_state(page, NR_SHMEM_PMDMAPPED);
    	} else {
    		if (PageTransCompound(page)) {
    			VM_BUG_ON_PAGE(!PageLocked(page), page);
    			SetPageDoubleMap(compound_head(page));
    			if (PageMlocked(page))
    				clear_page_mlock(compound_head(page));
    		}
    		if (!atomic_inc_and_test(&page->_mapcount))
    			goto out;
    	}
    	__mod_node_page_state(page_pgdat(page), NR_FILE_MAPPED, nr);
    	mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
    out:
    	unlock_page_memcg(page);
    }
    
    static void page_remove_file_rmap(struct page *page, bool compound)
    {
    	int i, nr = 1;
    
    	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
    	lock_page_memcg(page);
    
    	/* Hugepages are not counted in NR_FILE_MAPPED for now. */
    	if (unlikely(PageHuge(page))) {
    		/* hugetlb pages are always mapped with pmds */
    		atomic_dec(compound_mapcount_ptr(page));
    		goto out;
    	}
    
    	/* page still mapped by someone else? */
    	if (compound && PageTransHuge(page)) {
    		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
    			if (atomic_add_negative(-1, &page[i]._mapcount))
    				nr++;
    		}
    		if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
    			goto out;
    		VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
    		__dec_zone_page_state(page, NR_SHMEM_PMDMAPPED);
    	} else {
    		if (!atomic_add_negative(-1, &page->_mapcount))
    			goto out;
    	}
    
    	/*
    	 * We use the irq-unsafe __{inc|mod}_zone_page_state because
    	 * these counters are not modified in interrupt context, and
    	 * pte lock(a spinlock) is held, which implies preemption disabled.
    	 */
    	__mod_node_page_state(page_pgdat(page), NR_FILE_MAPPED, -nr);
    	mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_FILE_MAPPED);
    
    	if (unlikely(PageMlocked(page)))
    		clear_page_mlock(page);
    out:
    	unlock_page_memcg(page);
    }
    
    static void page_remove_anon_compound_rmap(struct page *page)
    {
    	int i, nr;
    
    	if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
    		return;
    
    	/* Hugepages are not counted in NR_ANON_PAGES for now. */
    	if (unlikely(PageHuge(page)))
    		return;
    
    	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
    		return;
    
    	__dec_zone_page_state(page, NR_ANON_THPS);
    
    	if (TestClearPageDoubleMap(page)) {
    		/*
    		 * Subpages can be mapped with PTEs too. Check how many of
    		 * themi are still mapped.
    		 */
    		for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
    			if (atomic_add_negative(-1, &page[i]._mapcount))
    				nr++;
    		}
    	} else {
    		nr = HPAGE_PMD_NR;
    	}
    
    	if (unlikely(PageMlocked(page)))
    		clear_page_mlock(page);
    
    	if (nr) {
    		__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
    		deferred_split_huge_page(page);
    	}
    }
    
    /**
     * page_remove_rmap - take down pte mapping from a page
     * @page:	page to remove mapping from
     * @compound:	uncharge the page as compound or small page
     *
     * The caller needs to hold the pte lock.
     */
    void page_remove_rmap(struct page *page, bool compound)
    {
    	if (!PageAnon(page))
    		return page_remove_file_rmap(page, compound);
    
    	if (compound)
    		return page_remove_anon_compound_rmap(page);
    
    	/* page still mapped by someone else? */
    	if (!atomic_add_negative(-1, &page->_mapcount))
    		return;
    
    	/*
    	 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
    	 * these counters are not modified in interrupt context, and
    	 * pte lock(a spinlock) is held, which implies preemption disabled.
    	 */
    	__dec_node_page_state(page, NR_ANON_MAPPED);
    
    	if (unlikely(PageMlocked(page)))
    		clear_page_mlock(page);
    
    	if (PageTransCompound(page))
    		deferred_split_huge_page(compound_head(page));
    
    	/*
    	 * It would be tidy to reset the PageAnon mapping here,
    	 * but that might overwrite a racing page_add_anon_rmap
    	 * which increments mapcount after us but sets mapping
    	 * before us: so leave the reset to free_hot_cold_page,
    	 * and remember that it's only reliable while mapped.
    	 * Leaving it set also helps swapoff to reinstate ptes
    	 * faster for those pages still in swapcache.
    	 */
    }
    
    struct rmap_private {
    	enum ttu_flags flags;
    	int lazyfreed;
    };
    
    /*
     * @arg: enum ttu_flags will be passed to this argument
     */
    static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
    		     unsigned long address, void *arg)
    {
    	struct mm_struct *mm = vma->vm_mm;
    	pte_t *pte;
    	pte_t pteval;
    	spinlock_t *ptl;
    	int ret = SWAP_AGAIN;
    	struct rmap_private *rp = arg;
    	enum ttu_flags flags = rp->flags;
    
    	/* munlock has nothing to gain from examining un-locked vmas */
    	if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
    		goto out;
    
    	if (flags & TTU_SPLIT_HUGE_PMD) {
    		split_huge_pmd_address(vma, address,
    				flags & TTU_MIGRATION, page);
    		/* check if we have anything to do after split */
    		if (page_mapcount(page) == 0)
    			goto out;
    	}
    
    	pte = page_check_address(page, mm, address, &ptl,
    				 PageTransCompound(page));
    	if (!pte)
    		goto out;
    
    	/*
    	 * If the page is mlock()d, we cannot swap it out.
    	 * If it's recently referenced (perhaps page_referenced
    	 * skipped over this mm) then we should reactivate it.
    	 */
    	if (!(flags & TTU_IGNORE_MLOCK)) {
    		if (vma->vm_flags & VM_LOCKED) {
    			/* PTE-mapped THP are never mlocked */
    			if (!PageTransCompound(page)) {
    				/*
    				 * Holding pte lock, we do *not* need
    				 * mmap_sem here
    				 */
    				mlock_vma_page(page);
    			}
    			ret = SWAP_MLOCK;
    			goto out_unmap;
    		}
    		if (flags & TTU_MUNLOCK)
    			goto out_unmap;
    	}
    	if (!(flags & TTU_IGNORE_ACCESS)) {
    		if (ptep_clear_flush_young_notify(vma, address, pte)) {
    			ret = SWAP_FAIL;
    			goto out_unmap;
    		}
      	}
    
    	/* Nuke the page table entry. */
    	flush_cache_page(vma, address, page_to_pfn(page));
    	if (should_defer_flush(mm, flags)) {
    		/*
    		 * We clear the PTE but do not flush so potentially a remote
    		 * CPU could still be writing to the page. If the entry was
    		 * previously clean then the architecture must guarantee that
    		 * a clear->dirty transition on a cached TLB entry is written
    		 * through and traps if the PTE is unmapped.
    		 */
    		pteval = ptep_get_and_clear(mm, address, pte);
    
    		set_tlb_ubc_flush_pending(mm, page, pte_dirty(pteval));
    	} else {
    		pteval = ptep_clear_flush(vma, address, pte);
    	}
    
    	/* Move the dirty bit to the physical page now the pte is gone. */
    	if (pte_dirty(pteval))
    		set_page_dirty(page);
    
    	/* Update high watermark before we lower rss */
    	update_hiwater_rss(mm);
    
    	if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
    		if (PageHuge(page)) {
    			hugetlb_count_sub(1 << compound_order(page), mm);
    		} else {
    			dec_mm_counter(mm, mm_counter(page));
    		}
    		set_pte_at(mm, address, pte,
    			   swp_entry_to_pte(make_hwpoison_entry(page)));
    	} else if (pte_unused(pteval)) {
    		/*
    		 * The guest indicated that the page content is of no
    		 * interest anymore. Simply discard the pte, vmscan
    		 * will take care of the rest.
    		 */
    		dec_mm_counter(mm, mm_counter(page));
    	} else if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION)) {
    		swp_entry_t entry;
    		pte_t swp_pte;
    		/*
    		 * Store the pfn of the page in a special migration
    		 * pte. do_swap_page() will wait until the migration
    		 * pte is removed and then restart fault handling.
    		 */
    		entry = make_migration_entry(page, pte_write(pteval));
    		swp_pte = swp_entry_to_pte(entry);
    		if (pte_soft_dirty(pteval))
    			swp_pte = pte_swp_mksoft_dirty(swp_pte);
    		set_pte_at(mm, address, pte, swp_pte);
    	} else if (PageAnon(page)) {
    		swp_entry_t entry = { .val = page_private(page) };
    		pte_t swp_pte;
    		/*
    		 * Store the swap location in the pte.
    		 * See handle_pte_fault() ...
    		 */
    		VM_BUG_ON_PAGE(!PageSwapCache(page), page);
    
    		if (!PageDirty(page) && (flags & TTU_LZFREE)) {
    			/* It's a freeable page by MADV_FREE */
    			dec_mm_counter(mm, MM_ANONPAGES);
    			rp->lazyfreed++;
    			goto discard;
    		}
    
    		if (swap_duplicate(entry) < 0) {
    			set_pte_at(mm, address, pte, pteval);
    			ret = SWAP_FAIL;
    			goto out_unmap;
    		}
    		if (list_empty(&mm->mmlist)) {
    			spin_lock(&mmlist_lock);
    			if (list_empty(&mm->mmlist))
    				list_add(&mm->mmlist, &init_mm.mmlist);
    			spin_unlock(&mmlist_lock);
    		}
    		dec_mm_counter(mm, MM_ANONPAGES);
    		inc_mm_counter(mm, MM_SWAPENTS);
    		swp_pte = swp_entry_to_pte(entry);
    		if (pte_soft_dirty(pteval))
    			swp_pte = pte_swp_mksoft_dirty(swp_pte);
    		set_pte_at(mm, address, pte, swp_pte);
    	} else
    		dec_mm_counter(mm, mm_counter_file(page));
    
    discard:
    	page_remove_rmap(page, PageHuge(page));
    	put_page(page);
    
    out_unmap:
    	pte_unmap_unlock(pte, ptl);
    	if (ret != SWAP_FAIL && ret != SWAP_MLOCK && !(flags & TTU_MUNLOCK))
    		mmu_notifier_invalidate_page(mm, address);
    out:
    	return ret;
    }
    
    bool is_vma_temporary_stack(struct vm_area_struct *vma)
    {
    	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
    
    	if (!maybe_stack)
    		return false;
    
    	if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
    						VM_STACK_INCOMPLETE_SETUP)
    		return true;
    
    	return false;
    }
    
    static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
    {
    	return is_vma_temporary_stack(vma);
    }
    
    static int page_mapcount_is_zero(struct page *page)
    {
    	return !page_mapcount(page);
    }
    
    /**
     * try_to_unmap - try to remove all page table mappings to a page
     * @page: the page to get unmapped
     * @flags: action and flags
     *
     * Tries to remove all the page table entries which are mapping this
     * page, used in the pageout path.  Caller must hold the page lock.
     * Return values are:
     *
     * SWAP_SUCCESS	- we succeeded in removing all mappings
     * SWAP_AGAIN	- we missed a mapping, try again later
     * SWAP_FAIL	- the page is unswappable
     * SWAP_MLOCK	- page is mlocked.
     */
    int try_to_unmap(struct page *page, enum ttu_flags flags)
    {
    	int ret;
    	struct rmap_private rp = {
    		.flags = flags,
    		.lazyfreed = 0,
    	};
    
    	struct rmap_walk_control rwc = {
    		.rmap_one = try_to_unmap_one,
    		.arg = &rp,
    		.done = page_mapcount_is_zero,
    		.anon_lock = page_lock_anon_vma_read,
    	};
    
    	/*
    	 * During exec, a temporary VMA is setup and later moved.
    	 * The VMA is moved under the anon_vma lock but not the
    	 * page tables leading to a race where migration cannot
    	 * find the migration ptes. Rather than increasing the
    	 * locking requirements of exec(), migration skips
    	 * temporary VMAs until after exec() completes.
    	 */
    	if ((flags & TTU_MIGRATION) && !PageKsm(page) && PageAnon(page))
    		rwc.invalid_vma = invalid_migration_vma;
    
    	if (flags & TTU_RMAP_LOCKED)
    		ret = rmap_walk_locked(page, &rwc);
    	else
    		ret = rmap_walk(page, &rwc);
    
    	if (ret != SWAP_MLOCK && !page_mapcount(page)) {
    		ret = SWAP_SUCCESS;
    		if (rp.lazyfreed && !PageDirty(page))
    			ret = SWAP_LZFREE;
    	}
    	return ret;
    }
    
    static int page_not_mapped(struct page *page)
    {
    	return !page_mapped(page);
    };
    
    /**
     * try_to_munlock - try to munlock a page
     * @page: the page to be munlocked
     *
     * Called from munlock code.  Checks all of the VMAs mapping the page
     * to make sure nobody else has this page mlocked. The page will be
     * returned with PG_mlocked cleared if no other vmas have it mlocked.
     *
     * Return values are:
     *
     * SWAP_AGAIN	- no vma is holding page mlocked, or,
     * SWAP_AGAIN	- page mapped in mlocked vma -- couldn't acquire mmap sem
     * SWAP_FAIL	- page cannot be located at present
     * SWAP_MLOCK	- page is now mlocked.
     */
    int try_to_munlock(struct page *page)
    {
    	int ret;
    	struct rmap_private rp = {
    		.flags = TTU_MUNLOCK,
    		.lazyfreed = 0,
    	};
    
    	struct rmap_walk_control rwc = {
    		.rmap_one = try_to_unmap_one,
    		.arg = &rp,
    		.done = page_not_mapped,
    		.anon_lock = page_lock_anon_vma_read,
    
    	};
    
    	VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
    
    	ret = rmap_walk(page, &rwc);
    	return ret;
    }
    
    void __put_anon_vma(struct anon_vma *anon_vma)
    {
    	struct anon_vma *root = anon_vma->root;
    
    	anon_vma_free(anon_vma);
    	if (root != anon_vma && atomic_dec_and_test(&root->refcount))
    		anon_vma_free(root);
    }
    
    static struct anon_vma *rmap_walk_anon_lock(struct page *page,
    					struct rmap_walk_control *rwc)
    {
    	struct anon_vma *anon_vma;
    
    	if (rwc->anon_lock)
    		return rwc->anon_lock(page);
    
    	/*
    	 * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
    	 * because that depends on page_mapped(); but not all its usages
    	 * are holding mmap_sem. Users without mmap_sem are required to
    	 * take a reference count to prevent the anon_vma disappearing
    	 */
    	anon_vma = page_anon_vma(page);
    	if (!anon_vma)
    		return NULL;
    
    	anon_vma_lock_read(anon_vma);
    	return anon_vma;
    }
    
    /*
     * rmap_walk_anon - do something to anonymous page using the object-based
     * rmap method
     * @page: the page to be handled
     * @rwc: control variable according to each walk type
     *
     * Find all the mappings of a page using the mapping pointer and the vma chains
     * contained in the anon_vma struct it points to.
     *
     * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
     * where the page was found will be held for write.  So, we won't recheck
     * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
     * LOCKED.
     */
    static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,
    		bool locked)
    {
    	struct anon_vma *anon_vma;
    	pgoff_t pgoff;
    	struct anon_vma_chain *avc;
    	int ret = SWAP_AGAIN;
    
    	if (locked) {
    		anon_vma = page_anon_vma(page);
    		/* anon_vma disappear under us? */
    		VM_BUG_ON_PAGE(!anon_vma, page);
    	} else {
    		anon_vma = rmap_walk_anon_lock(page, rwc);
    	}
    	if (!anon_vma)
    		return ret;
    
    	pgoff = page_to_pgoff(page);
    	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
    		struct vm_area_struct *vma = avc->vma;
    		unsigned long address = vma_address(page, vma);
    
    		cond_resched();
    
    		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
    			continue;
    
    		ret = rwc->rmap_one(page, vma, address, rwc->arg);
    		if (ret != SWAP_AGAIN)
    			break;
    		if (rwc->done && rwc->done(page))
    			break;
    	}
    
    	if (!locked)
    		anon_vma_unlock_read(anon_vma);
    	return ret;
    }
    
    /*
     * rmap_walk_file - do something to file page using the object-based rmap method
     * @page: the page to be handled
     * @rwc: control variable according to each walk type
     *
     * Find all the mappings of a page using the mapping pointer and the vma chains
     * contained in the address_space struct it points to.
     *
     * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
     * where the page was found will be held for write.  So, we won't recheck
     * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
     * LOCKED.
     */
    static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,
    		bool locked)
    {
    	struct address_space *mapping = page_mapping(page);
    	pgoff_t pgoff;
    	struct vm_area_struct *vma;
    	int ret = SWAP_AGAIN;
    
    	/*
    	 * The page lock not only makes sure that page->mapping cannot
    	 * suddenly be NULLified by truncation, it makes sure that the
    	 * structure at mapping cannot be freed and reused yet,
    	 * so we can safely take mapping->i_mmap_rwsem.
    	 */
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    
    	if (!mapping)
    		return ret;
    
    	pgoff = page_to_pgoff(page);
    	if (!locked)
    		i_mmap_lock_read(mapping);
    	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
    		unsigned long address = vma_address(page, vma);
    
    		cond_resched();
    
    		if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
    			continue;
    
    		ret = rwc->rmap_one(page, vma, address, rwc->arg);
    		if (ret != SWAP_AGAIN)
    			goto done;
    		if (rwc->done && rwc->done(page))
    			goto done;
    	}
    
    done:
    	if (!locked)
    		i_mmap_unlock_read(mapping);
    	return ret;
    }
    
    int rmap_walk(struct page *page, struct rmap_walk_control *rwc)
    {
    	if (unlikely(PageKsm(page)))
    		return rmap_walk_ksm(page, rwc);
    	else if (PageAnon(page))
    		return rmap_walk_anon(page, rwc, false);
    	else
    		return rmap_walk_file(page, rwc, false);
    }
    
    /* Like rmap_walk, but caller holds relevant rmap lock */
    int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc)
    {
    	/* no ksm support for now */
    	VM_BUG_ON_PAGE(PageKsm(page), page);
    	if (PageAnon(page))
    		return rmap_walk_anon(page, rwc, true);
    	else
    		return rmap_walk_file(page, rwc, true);
    }
    
    #ifdef CONFIG_HUGETLB_PAGE
    /*
     * The following three functions are for anonymous (private mapped) hugepages.
     * Unlike common anonymous pages, anonymous hugepages have no accounting code
     * and no lru code, because we handle hugepages differently from common pages.
     */
    static void __hugepage_set_anon_rmap(struct page *page,
    	struct vm_area_struct *vma, unsigned long address, int exclusive)
    {
    	struct anon_vma *anon_vma = vma->anon_vma;
    
    	BUG_ON(!anon_vma);
    
    	if (PageAnon(page))
    		return;
    	if (!exclusive)
    		anon_vma = anon_vma->root;
    
    	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
    	page->mapping = (struct address_space *) anon_vma;
    	page->index = linear_page_index(vma, address);
    }
    
    void hugepage_add_anon_rmap(struct page *page,
    			    struct vm_area_struct *vma, unsigned long address)
    {
    	struct anon_vma *anon_vma = vma->anon_vma;
    	int first;
    
    	BUG_ON(!PageLocked(page));
    	BUG_ON(!anon_vma);
    	/* address might be in next vma when migration races vma_adjust */
    	first = atomic_inc_and_test(compound_mapcount_ptr(page));
    	if (first)
    		__hugepage_set_anon_rmap(page, vma, address, 0);
    }
    
    void hugepage_add_new_anon_rmap(struct page *page,
    			struct vm_area_struct *vma, unsigned long address)
    {
    	BUG_ON(address < vma->vm_start || address >= vma->vm_end);
    	atomic_set(compound_mapcount_ptr(page), 0);
    	__hugepage_set_anon_rmap(page, vma, address, 1);
    }
    #endif /* CONFIG_HUGETLB_PAGE */