rmap.c

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/*
 * mm/rmap.c - physical to virtual reverse mappings
 *
 * Copyright 2001, Rik van Riel <[email protected]>
 * 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 <[email protected]> 2001
 * File methods by Dave McCracken <[email protected]> 2003, 2004
 * Anonymous methods by Andrea Arcangeli <[email protected]> 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)
 *       mapping->i_mmap_mutex
 *         anon_vma->mutex
 *           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)
 *               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->mutex,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 <asm/tlbflush.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);
        /*
         * 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() 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
     * mutex_trylock() from page_lock_anon_vma(). This orders:
     *
     * page_lock_anon_vma()     VS  put_anon_vma()
     *   mutex_trylock()              atomic_dec_and_test()
     *   LOCK                 MB
     *   atomic_read()            mutex_is_locked()
     *
     * LOCK should suffice since the actual taking of the lock must
     * happen _before_ what follows.
     */
    if (mutex_is_locked(&anon_vma->root->mutex)) {
        anon_vma_lock(anon_vma);
        anon_vma_unlock(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);
}

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(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);
            allocated = NULL;
            avc = NULL;
        }
        spin_unlock(&mm->page_table_lock);
        anon_vma_unlock(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))
            mutex_unlock(&root->mutex);
        root = new_root;
        mutex_lock(&root->mutex);
    }
    return root;
}

static inline void unlock_anon_vma_root(struct anon_vma *root)
{
    if (root)
        mutex_unlock(&root->mutex);
}

/*
 * Attach the anon_vmas from src to dst.
 * Returns 0 on success, -ENOMEM on failure.
 */
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);
    }
    unlock_anon_vma_root(root);
    return 0;

 enomem_failure:
    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;

    /* Don't bother if the parent process has no anon_vma here. */
    if (!pvma->anon_vma)
        return 0;

    /*
     * First, attach the new VMA to the parent VMA's anon_vmas,
     * so rmap can find non-COWed pages in child processes.
     */
    if (anon_vma_clone(vma, pvma))
        return -ENOMEM;

    /* 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;
    /*
     * 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(anon_vma);
    anon_vma_chain_link(vma, avc, anon_vma);
    anon_vma_unlock(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))
            continue;

        list_del(&avc->same_vma);
        anon_vma_chain_free(avc);
    }
    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 acquire the anon_vma->root->mutex.
     */
    list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
        struct anon_vma *anon_vma = avc->anon_vma;

        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;

    mutex_init(&anon_vma->mutex);
    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, anon_vma_ctor);
    anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
}

/*
 * 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) ACCESS_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)) {
        put_anon_vma(anon_vma);
        anon_vma = 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(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) ACCESS_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 = ACCESS_ONCE(anon_vma->root);
    if (mutex_trylock(&root_anon_vma->mutex)) {
        /*
         * 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)) {
            mutex_unlock(&root_anon_vma->mutex);
            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)) {
        put_anon_vma(anon_vma);
        anon_vma = NULL;
        goto out;
    }

    /* we pinned the anon_vma, its safe to sleep */
    rcu_read_unlock();
    anon_vma_lock(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() recursion.
         */
        anon_vma_unlock(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(struct anon_vma *anon_vma)
{
    anon_vma_unlock(anon_vma);
}

/*
 * At what user virtual address is page expected in @vma?
 */
static inline unsigned long
__vma_address(struct page *page, struct vm_area_struct *vma)
{
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

    if (unlikely(is_vm_hugetlb_page(vma)))
        pgoff = page->index << huge_page_order(page_hstate(page));

    return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
}

inline unsigned long
vma_address(struct page *page, struct vm_area_struct *vma)
{
    unsigned long address = __vma_address(page, vma);

    /* page should be within @vma mapping range */
    VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);

    return address;
}

/*
 * 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 && !(vma->vm_flags & VM_NONLINEAR)) {
        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;
}

/*
 * 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)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    spinlock_t *ptl;

    if (unlikely(PageHuge(page))) {
        pte = huge_pte_offset(mm, address);
        ptl = &mm->page_table_lock;
        goto check;
    }

    pgd = pgd_offset(mm, address);
    if (!pgd_present(*pgd))
        return NULL;

    pud = pud_offset(pgd, address);
    if (!pud_present(*pud))
        return NULL;

    pmd = pmd_offset(pud, address);
    if (!pmd_present(*pmd))
        return NULL;
    if (pmd_trans_huge(*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;
}

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;
}

/*
 * Subfunctions of page_referenced: page_referenced_one called
 * repeatedly from either page_referenced_anon or page_referenced_file.
 */
int page_referenced_one(struct page *page, struct vm_area_struct *vma,
            unsigned long address, unsigned int *mapcount,
            unsigned long *vm_flags)
{
    struct mm_struct *mm = vma->vm_mm;
    int referenced = 0;

    if (unlikely(PageTransHuge(page))) {
        pmd_t *pmd;

        spin_lock(&mm->page_table_lock);
        /*
         * rmap might return false positives; we must filter
         * these out using page_check_address_pmd().
         */
        pmd = page_check_address_pmd(page, mm, address,
                         PAGE_CHECK_ADDRESS_PMD_FLAG);
        if (!pmd) {
            spin_unlock(&mm->page_table_lock);
            goto out;
        }

        if (vma->vm_flags & VM_LOCKED) {
            spin_unlock(&mm->page_table_lock);
            *mapcount = 0;  /* break early from loop */
            *vm_flags |= VM_LOCKED;
            goto out;
        }

        /* go ahead even if the pmd is pmd_trans_splitting() */
        if (pmdp_clear_flush_young_notify(vma, address, pmd))
            referenced++;
        spin_unlock(&mm->page_table_lock);
    } else {
        pte_t *pte;
        spinlock_t *ptl;

        /*
         * rmap might return false positives; we must filter
         * these out using page_check_address().
         */
        pte = page_check_address(page, mm, address, &ptl, 0);
        if (!pte)
            goto out;

        if (vma->vm_flags & VM_LOCKED) {
            pte_unmap_unlock(pte, ptl);
            *mapcount = 0;  /* break early from loop */
            *vm_flags |= VM_LOCKED;
            goto out;
        }

        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(!VM_SequentialReadHint(vma)))
                referenced++;
        }
        pte_unmap_unlock(pte, ptl);
    }

    (*mapcount)--;

    if (referenced)
        *vm_flags |= vma->vm_flags;
out:
    return referenced;
}

static int page_referenced_anon(struct page *page,
                struct mem_cgroup *memcg,
                unsigned long *vm_flags)
{
    unsigned int mapcount;
    struct anon_vma *anon_vma;
    pgoff_t pgoff;
    struct anon_vma_chain *avc;
    int referenced = 0;

    anon_vma = page_lock_anon_vma(page);
    if (!anon_vma)
        return referenced;

    mapcount = page_mapcount(page);
    pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    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);
        /*
         * If we are reclaiming on behalf of a cgroup, skip
         * counting on behalf of references from different
         * cgroups
         */
        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
            continue;
        referenced += page_referenced_one(page, vma, address,
                          &mapcount, vm_flags);
        if (!mapcount)
            break;
    }

    page_unlock_anon_vma(anon_vma);
    return referenced;
}

static int page_referenced_file(struct page *page,
                struct mem_cgroup *memcg,
                unsigned long *vm_flags)
{
    unsigned int mapcount;
    struct address_space *mapping = page->mapping;
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    struct vm_area_struct *vma;
    int referenced = 0;

    /*
     * The caller's checks on page->mapping and !PageAnon have made
     * sure that this is a file page: the check for page->mapping
     * excludes the case just before it gets set on an anon page.
     */
    BUG_ON(PageAnon(page));

    /*
     * 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_mutex.
     */
    BUG_ON(!PageLocked(page));

    mutex_lock(&mapping->i_mmap_mutex);

    /*
     * i_mmap_mutex does not stabilize mapcount at all, but mapcount
     * is more likely to be accurate if we note it after spinning.
     */
    mapcount = page_mapcount(page);

    vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
        unsigned long address = vma_address(page, vma);
        /*
         * If we are reclaiming on behalf of a cgroup, skip
         * counting on behalf of references from different
         * cgroups
         */
        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
            continue;
        referenced += page_referenced_one(page, vma, address,
                          &mapcount, vm_flags);
        if (!mapcount)
            break;
    }

    mutex_unlock(&mapping->i_mmap_mutex);
    return referenced;
}

int page_referenced(struct page *page,
            int is_locked,
            struct mem_cgroup *memcg,
            unsigned long *vm_flags)
{
    int referenced = 0;
    int we_locked = 0;

    *vm_flags = 0;
    if (page_mapped(page) && page_rmapping(page)) {
        if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
            we_locked = trylock_page(page);
            if (!we_locked) {
                referenced++;
                goto out;
            }
        }
        if (unlikely(PageKsm(page)))
            referenced += page_referenced_ksm(page, memcg,
                                vm_flags);
        else if (PageAnon(page))
            referenced += page_referenced_anon(page, memcg,
                                vm_flags);
        else if (page->mapping)
            referenced += page_referenced_file(page, memcg,
                                vm_flags);
        if (we_locked)
            unlock_page(page);

        if (page_test_and_clear_young(page_to_pfn(page)))
            referenced++;
    }
out:
    return referenced;
}

static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
                unsigned long address)
{
    struct mm_struct *mm = vma->vm_mm;
    pte_t *pte;
    spinlock_t *ptl;
    int ret = 0;

    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);
out:
    return ret;
}

static int page_mkclean_file(struct address_space *mapping, struct page *page)
{
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    struct vm_area_struct *vma;
    int ret = 0;

    BUG_ON(PageAnon(page));

    mutex_lock(&mapping->i_mmap_mutex);
    vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
        if (vma->vm_flags & VM_SHARED) {
            unsigned long address = vma_address(page, vma);
            ret += page_mkclean_one(page, vma, address);
        }
    }
    mutex_unlock(&mapping->i_mmap_mutex);
    return ret;
}

int page_mkclean(struct page *page)
{
    int ret = 0;

    BUG_ON(!PageLocked(page));

    if (page_mapped(page)) {
        struct address_space *mapping = page_mapping(page);
        if (mapping)
            ret = page_mkclean_file(mapping, page);
    }

    return ret;
}
EXPORT_SYMBOL_GPL(page_mkclean);

void page_move_anon_rmap(struct page *page,
    struct vm_area_struct *vma, unsigned long address)
{
    struct anon_vma *anon_vma = vma->anon_vma;

    VM_BUG_ON(!PageLocked(page));
    VM_BUG_ON(!anon_vma);
    VM_BUG_ON(page->index != linear_page_index(vma, address));

    anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
    page->mapping = (struct address_space *) anon_vma;
}

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);
}

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->index != linear_page_index(vma, address));
#endif
}

void page_add_anon_rmap(struct page *page,
    struct vm_area_struct *vma, unsigned long address)
{
    do_page_add_anon_rmap(page, vma, address, 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 exclusive)
{
    int first = atomic_inc_and_test(&page->_mapcount);
    if (first) {
        if (!PageTransHuge(page))
            __inc_zone_page_state(page, NR_ANON_PAGES);
        else
            __inc_zone_page_state(page,
                          NR_ANON_TRANSPARENT_HUGEPAGES);
    }
    if (unlikely(PageKsm(page)))
        return;

    VM_BUG_ON(!PageLocked(page));
    /* address might be in next vma when migration races vma_adjust */
    if (first)
        __page_set_anon_rmap(page, vma, address, exclusive);
    else
        __page_check_anon_rmap(page, vma, address);
}

void page_add_new_anon_rmap(struct page *page,
    struct vm_area_struct *vma, unsigned long address)
{
    VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
    SetPageSwapBacked(page);
    atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
    if (!PageTransHuge(page))
        __inc_zone_page_state(page, NR_ANON_PAGES);
    else
        __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
    __page_set_anon_rmap(page, vma, address, 1);
    if (!mlocked_vma_newpage(vma, page))
        lru_cache_add_lru(page, LRU_ACTIVE_ANON);
    else
        add_page_to_unevictable_list(page);
}

void page_add_file_rmap(struct page *page)
{
    bool locked;
    unsigned long flags;

    mem_cgroup_begin_update_page_stat(page, &locked, &flags);
    if (atomic_inc_and_test(&page->_mapcount)) {
        __inc_zone_page_state(page, NR_FILE_MAPPED);
        mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
    }
    mem_cgroup_end_update_page_stat(page, &locked, &flags);
}

void page_remove_rmap(struct page *page)
{
    struct address_space *mapping = page_mapping(page);
    bool anon = PageAnon(page);
    bool locked;
    unsigned long flags;

    /*
     * The anon case has no mem_cgroup page_stat to update; but may
     * uncharge_page() below, where the lock ordering can deadlock if
     * we hold the lock against page_stat move: so avoid it on anon.
     */
    if (!anon)
        mem_cgroup_begin_update_page_stat(page, &locked, &flags);

    /* page still mapped by someone else? */
    if (!atomic_add_negative(-1, &page->_mapcount))
        goto out;

    /*
     * Now that the last pte has gone, s390 must transfer dirty
     * flag from storage key to struct page.  We can usually skip
     * this if the page is anon, so about to be freed; but perhaps
     * not if it's in swapcache - there might be another pte slot
     * containing the swap entry, but page not yet written to swap.
     *
     * And we can skip it on file pages, so long as the filesystem
     * participates in dirty tracking; but need to catch shm and tmpfs
     * and ramfs pages which have been modified since creation by read
     * fault.
     *
     * Note that mapping must be decided above, before decrementing
     * mapcount (which luckily provides a barrier): once page is unmapped,
     * it could be truncated and page->mapping reset to NULL at any moment.
     * Note also that we are relying on page_mapping(page) to set mapping
     * to &swapper_space when PageSwapCache(page).
     */
    if (mapping && !mapping_cap_account_dirty(mapping) &&
        page_test_and_clear_dirty(page_to_pfn(page), 1))
        set_page_dirty(page);
    /*
     * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
     * and not charged by memcg for now.
     */
    if (unlikely(PageHuge(page)))
        goto out;
    if (anon) {
        mem_cgroup_uncharge_page(page);
        if (!PageTransHuge(page))
            __dec_zone_page_state(page, NR_ANON_PAGES);
        else
            __dec_zone_page_state(page,
                          NR_ANON_TRANSPARENT_HUGEPAGES);
    } else {
        __dec_zone_page_state(page, NR_FILE_MAPPED);
        mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
        mem_cgroup_end_update_page_stat(page, &locked, &flags);
    }
    if (unlikely(PageMlocked(page)))
        clear_page_mlock(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.
     */
    return;
out:
    if (!anon)
        mem_cgroup_end_update_page_stat(page, &locked, &flags);
}

/*
 * Subfunctions of try_to_unmap: try_to_unmap_one called
 * repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
 */
int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
             unsigned long address, enum ttu_flags flags)
{
    struct mm_struct *mm = vma->vm_mm;
    pte_t *pte;
    pte_t pteval;
    spinlock_t *ptl;
    int ret = SWAP_AGAIN;

    pte = page_check_address(page, mm, address, &ptl, 0);
    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)
            goto out_mlock;

        if (TTU_ACTION(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));
    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 (PageAnon(page))
            dec_mm_counter(mm, MM_ANONPAGES);
        else
            dec_mm_counter(mm, MM_FILEPAGES);
        set_pte_at(mm, address, pte,
                swp_entry_to_pte(make_hwpoison_entry(page)));
    } else if (PageAnon(page)) {
        swp_entry_t entry = { .val = page_private(page) };

        if (PageSwapCache(page)) {
            /*
             * Store the swap location in the pte.
             * See handle_pte_fault() ...
             */
            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);
        } else if (IS_ENABLED(CONFIG_MIGRATION)) {
            /*
             * 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.
             */
            BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
            entry = make_migration_entry(page, pte_write(pteval));
        }
        set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
        BUG_ON(pte_file(*pte));
    } else if (IS_ENABLED(CONFIG_MIGRATION) &&
           (TTU_ACTION(flags) == TTU_MIGRATION)) {
        /* Establish migration entry for a file page */
        swp_entry_t entry;
        entry = make_migration_entry(page, pte_write(pteval));
        set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
    } else
        dec_mm_counter(mm, MM_FILEPAGES);

    page_remove_rmap(page);
    page_cache_release(page);

out_unmap:
    pte_unmap_unlock(pte, ptl);
    if (ret != SWAP_FAIL)
        mmu_notifier_invalidate_page(mm, address);
out:
    return ret;

out_mlock:
    pte_unmap_unlock(pte, ptl);


    /*
     * We need mmap_sem locking, Otherwise VM_LOCKED check makes
     * unstable result and race. Plus, We can't wait here because
     * we now hold anon_vma->mutex or mapping->i_mmap_mutex.
     * if trylock failed, the page remain in evictable lru and later
     * vmscan could retry to move the page to unevictable lru if the
     * page is actually mlocked.
     */
    if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
        if (vma->vm_flags & VM_LOCKED) {
            mlock_vma_page(page);
            ret = SWAP_MLOCK;
        }
        up_read(&vma->vm_mm->mmap_sem);
    }
    return ret;
}

/*
 * objrmap doesn't work for nonlinear VMAs because the assumption that
 * offset-into-file correlates with offset-into-virtual-addresses does not hold.
 * Consequently, given a particular page and its ->index, we cannot locate the
 * ptes which are mapping that page without an exhaustive linear search.
 *
 * So what this code does is a mini "virtual scan" of each nonlinear VMA which
 * maps the file to which the target page belongs.  The ->vm_private_data field
 * holds the current cursor into that scan.  Successive searches will circulate
 * around the vma's virtual address space.
 *
 * So as more replacement pressure is applied to the pages in a nonlinear VMA,
 * more scanning pressure is placed against them as well.   Eventually pages
 * will become fully unmapped and are eligible for eviction.
 *
 * For very sparsely populated VMAs this is a little inefficient - chances are
 * there there won't be many ptes located within the scan cluster.  In this case
 * maybe we could scan further - to the end of the pte page, perhaps.
 *
 * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
 * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
 * rather than unmapping them.  If we encounter the "check_page" that vmscan is
 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
 */
#define CLUSTER_SIZE    min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK    (~(CLUSTER_SIZE - 1))

static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
        struct vm_area_struct *vma, struct page *check_page)
{
    struct mm_struct *mm = vma->vm_mm;
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    pte_t pteval;
    spinlock_t *ptl;
    struct page *page;
    unsigned long address;
    unsigned long mmun_start;   /* For mmu_notifiers */
    unsigned long mmun_end;     /* For mmu_notifiers */
    unsigned long end;
    int ret = SWAP_AGAIN;
    int locked_vma = 0;

    address = (vma->vm_start + cursor) & CLUSTER_MASK;
    end = address + CLUSTER_SIZE;
    if (address < vma->vm_start)
        address = vma->vm_start;
    if (end > vma->vm_end)
        end = vma->vm_end;

    pgd = pgd_offset(mm, address);
    if (!pgd_present(*pgd))
        return ret;

    pud = pud_offset(pgd, address);
    if (!pud_present(*pud))
        return ret;

    pmd = pmd_offset(pud, address);
    if (!pmd_present(*pmd))
        return ret;

    mmun_start = address;
    mmun_end   = end;
    mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);

    /*
     * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
     * keep the sem while scanning the cluster for mlocking pages.
     */
    if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
        locked_vma = (vma->vm_flags & VM_LOCKED);
        if (!locked_vma)
            up_read(&vma->vm_mm->mmap_sem); /* don't need it */
    }

    pte = pte_offset_map_lock(mm, pmd, address, &ptl);

    /* Update high watermark before we lower rss */
    update_hiwater_rss(mm);

    for (; address < end; pte++, address += PAGE_SIZE) {
        if (!pte_present(*pte))
            continue;
        page = vm_normal_page(vma, address, *pte);
        BUG_ON(!page || PageAnon(page));

        if (locked_vma) {
            mlock_vma_page(page);   /* no-op if already mlocked */
            if (page == check_page)
                ret = SWAP_MLOCK;
            continue;   /* don't unmap */
        }

        if (ptep_clear_flush_young_notify(vma, address, pte))
            continue;

        /* Nuke the page table entry. */
        flush_cache_page(vma, address, pte_pfn(*pte));
        pteval = ptep_clear_flush(vma, address, pte);

        /* If nonlinear, store the file page offset in the pte. */
        if (page->index != linear_page_index(vma, address))
            set_pte_at(mm, address, pte, pgoff_to_pte(page->index));

        /* Move the dirty bit to the physical page now the pte is gone. */
        if (pte_dirty(pteval))
            set_page_dirty(page);

        page_remove_rmap(page);
        page_cache_release(page);
        dec_mm_counter(mm, MM_FILEPAGES);
        (*mapcount)--;
    }
    pte_unmap_unlock(pte - 1, ptl);
    mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
    if (locked_vma)
        up_read(&vma->vm_mm->mmap_sem);
    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 int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
{
    struct anon_vma *anon_vma;
    pgoff_t pgoff;
    struct anon_vma_chain *avc;
    int ret = SWAP_AGAIN;

    anon_vma = page_lock_anon_vma(page);
    if (!anon_vma)
        return ret;

    pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
        struct vm_area_struct *vma = avc->vma;
        unsigned long address;

        /*
         * 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 (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
                is_vma_temporary_stack(vma))
            continue;

        address = vma_address(page, vma);
        ret = try_to_unmap_one(page, vma, address, flags);
        if (ret != SWAP_AGAIN || !page_mapped(page))
            break;
    }

    page_unlock_anon_vma(anon_vma);
    return ret;
}

static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
{
    struct address_space *mapping = page->mapping;
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    struct vm_area_struct *vma;
    int ret = SWAP_AGAIN;
    unsigned long cursor;
    unsigned long max_nl_cursor = 0;
    unsigned long max_nl_size = 0;
    unsigned int mapcount;

    mutex_lock(&mapping->i_mmap_mutex);
    vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
        unsigned long address = vma_address(page, vma);
        ret = try_to_unmap_one(page, vma, address, flags);
        if (ret != SWAP_AGAIN || !page_mapped(page))
            goto out;
    }

    if (list_empty(&mapping->i_mmap_nonlinear))
        goto out;

    /*
     * We don't bother to try to find the munlocked page in nonlinears.
     * It's costly. Instead, later, page reclaim logic may call
     * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
     */
    if (TTU_ACTION(flags) == TTU_MUNLOCK)
        goto out;

    list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
                            shared.nonlinear) {
        cursor = (unsigned long) vma->vm_private_data;
        if (cursor > max_nl_cursor)
            max_nl_cursor = cursor;
        cursor = vma->vm_end - vma->vm_start;
        if (cursor > max_nl_size)
            max_nl_size = cursor;
    }

    if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
        ret = SWAP_FAIL;
        goto out;
    }

    /*
     * We don't try to search for this page in the nonlinear vmas,
     * and page_referenced wouldn't have found it anyway.  Instead
     * just walk the nonlinear vmas trying to age and unmap some.
     * The mapcount of the page we came in with is irrelevant,
     * but even so use it as a guide to how hard we should try?
     */
    mapcount = page_mapcount(page);
    if (!mapcount)
        goto out;
    cond_resched();

    max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
    if (max_nl_cursor == 0)
        max_nl_cursor = CLUSTER_SIZE;

    do {
        list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
                            shared.nonlinear) {
            cursor = (unsigned long) vma->vm_private_data;
            while ( cursor < max_nl_cursor &&
                cursor < vma->vm_end - vma->vm_start) {
                if (try_to_unmap_cluster(cursor, &mapcount,
                        vma, page) == SWAP_MLOCK)
                    ret = SWAP_MLOCK;
                cursor += CLUSTER_SIZE;
                vma->vm_private_data = (void *) cursor;
                if ((int)mapcount <= 0)
                    goto out;
            }
            vma->vm_private_data = (void *) max_nl_cursor;
        }
        cond_resched();
        max_nl_cursor += CLUSTER_SIZE;
    } while (max_nl_cursor <= max_nl_size);

    /*
     * Don't loop forever (perhaps all the remaining pages are
     * in locked vmas).  Reset cursor on all unreserved nonlinear
     * vmas, now forgetting on which ones it had fallen behind.
     */
    list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.nonlinear)
        vma->vm_private_data = NULL;
out:
    mutex_unlock(&mapping->i_mmap_mutex);
    return ret;
}

int try_to_unmap(struct page *page, enum ttu_flags flags)
{
    int ret;

    BUG_ON(!PageLocked(page));
    VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));

    if (unlikely(PageKsm(page)))
        ret = try_to_unmap_ksm(page, flags);
    else if (PageAnon(page))
        ret = try_to_unmap_anon(page, flags);
    else
        ret = try_to_unmap_file(page, flags);
    if (ret != SWAP_MLOCK && !page_mapped(page))
        ret = SWAP_SUCCESS;
    return ret;
}

int try_to_munlock(struct page *page)
{
    VM_BUG_ON(!PageLocked(page) || PageLRU(page));

    if (unlikely(PageKsm(page)))
        return try_to_unmap_ksm(page, TTU_MUNLOCK);
    else if (PageAnon(page))
        return try_to_unmap_anon(page, TTU_MUNLOCK);
    else
        return try_to_unmap_file(page, TTU_MUNLOCK);
}

void __put_anon_vma(struct anon_vma *anon_vma)
{
    struct anon_vma *root = anon_vma->root;

    if (root != anon_vma && atomic_dec_and_test(&root->refcount))
        anon_vma_free(root);

    anon_vma_free(anon_vma);
}

#ifdef CONFIG_MIGRATION
/*
 * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
 * Called by migrate.c to remove migration ptes, but might be used more later.
 */
static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
        struct vm_area_struct *, unsigned long, void *), void *arg)
{
    struct anon_vma *anon_vma;
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    struct anon_vma_chain *avc;
    int ret = SWAP_AGAIN;

    /*
     * Note: remove_migration_ptes() cannot use page_lock_anon_vma()
     * 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 ret;
    anon_vma_lock(anon_vma);
    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);
        ret = rmap_one(page, vma, address, arg);
        if (ret != SWAP_AGAIN)
            break;
    }
    anon_vma_unlock(anon_vma);
    return ret;
}

static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
        struct vm_area_struct *, unsigned long, void *), void *arg)
{
    struct address_space *mapping = page->mapping;
    pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
    struct vm_area_struct *vma;
    int ret = SWAP_AGAIN;

    if (!mapping)
        return ret;
    mutex_lock(&mapping->i_mmap_mutex);
    vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
        unsigned long address = vma_address(page, vma);
        ret = rmap_one(page, vma, address, arg);
        if (ret != SWAP_AGAIN)
            break;
    }
    /*
     * No nonlinear handling: being always shared, nonlinear vmas
     * never contain migration ptes.  Decide what to do about this
     * limitation to linear when we need rmap_walk() on nonlinear.
     */
    mutex_unlock(&mapping->i_mmap_mutex);
    return ret;
}

int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
        struct vm_area_struct *, unsigned long, void *), void *arg)
{
    VM_BUG_ON(!PageLocked(page));

    if (unlikely(PageKsm(page)))
        return rmap_walk_ksm(page, rmap_one, arg);
    else if (PageAnon(page))
        return rmap_walk_anon(page, rmap_one, arg);
    else
        return rmap_walk_file(page, rmap_one, arg);
}
#endif /* CONFIG_MIGRATION */

#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(&page->_mapcount);
    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(&page->_mapcount, 0);
    __hugepage_set_anon_rmap(page, vma, address, 1);
}
#endif /* CONFIG_HUGETLB_PAGE */