1 files changed, 199 insertions, 151 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index dd43373a483f..98135dbd25ba 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -49,6 +49,7 @@
 #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/module.h>
@@ -67,7 +68,7 @@ static inline struct anon_vma *anon_vma_alloc(void)
         return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
 }
 
-static inline void anon_vma_free(struct anon_vma *anon_vma)
+void anon_vma_free(struct anon_vma *anon_vma)
 {
         kmem_cache_free(anon_vma_cachep, anon_vma);
 }
@@ -171,7 +172,7 @@ void anon_vma_unlink(struct vm_area_struct *vma)
         list_del(&vma->anon_vma_node);
 
         /* We must garbage collect the anon_vma if it's empty */
-        empty = list_empty(&anon_vma->head);
+        empty = list_empty(&anon_vma->head) && !ksm_refcount(anon_vma);
         spin_unlock(&anon_vma->lock);
 
         if (empty)
@@ -183,6 +184,7 @@ static void anon_vma_ctor(void *data)
         struct anon_vma *anon_vma = data;
 
         spin_lock_init(&anon_vma->lock);
+        ksm_refcount_init(anon_vma);
         INIT_LIST_HEAD(&anon_vma->head);
 }
 
@@ -202,8 +204,8 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
         unsigned long anon_mapping;
 
         rcu_read_lock();
-        anon_mapping = (unsigned long) page->mapping;
-        if (!(anon_mapping & PAGE_MAPPING_ANON))
+        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;
@@ -248,8 +250,7 @@ vma_address(struct page *page, struct vm_area_struct *vma)
 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 {
         if (PageAnon(page)) {
-                if ((void *)vma->anon_vma !=
-                    (void *)page->mapping - PAGE_MAPPING_ANON)
+                if (vma->anon_vma != page_anon_vma(page))
                         return -EFAULT;
         } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
                 if (!vma->vm_file ||
@@ -337,21 +338,15 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
  * Subfunctions of page_referenced: page_referenced_one called
  * repeatedly from either page_referenced_anon or page_referenced_file.
  */
-static int page_referenced_one(struct page *page,
-                               struct vm_area_struct *vma,
-                               unsigned int *mapcount,
-                               unsigned long *vm_flags)
+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;
-        unsigned long address;
         pte_t *pte;
         spinlock_t *ptl;
         int referenced = 0;
 
-        address = vma_address(page, vma);
-        if (address == -EFAULT)
-                goto out;
-
         pte = page_check_address(page, mm, address, &ptl, 0);
         if (!pte)
                 goto out;
@@ -388,9 +383,10 @@ static int page_referenced_one(struct page *page,
 out_unmap:
         (*mapcount)--;
         pte_unmap_unlock(pte, ptl);
-out:
+
         if (referenced)
                 *vm_flags |= vma->vm_flags;
+out:
         return referenced;
 }
 
@@ -409,6 +405,9 @@ static int page_referenced_anon(struct page *page,
 
         mapcount = page_mapcount(page);
         list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
                 /*
                  * If we are reclaiming on behalf of a cgroup, skip
                  * counting on behalf of references from different
@@ -416,7 +415,7 @@ static int page_referenced_anon(struct page *page,
                  */
                 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
                         continue;
-                referenced += page_referenced_one(page, vma,
+                referenced += page_referenced_one(page, vma, address,
                                                   &mapcount, vm_flags);
                 if (!mapcount)
                         break;
@@ -474,6 +473,9 @@ static int page_referenced_file(struct page *page,
         mapcount = page_mapcount(page);
 
         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
                 /*
                  * If we are reclaiming on behalf of a cgroup, skip
                  * counting on behalf of references from different
@@ -481,7 +483,7 @@ static int page_referenced_file(struct page *page,
                  */
                 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
                         continue;
-                referenced += page_referenced_one(page, vma,
+                referenced += page_referenced_one(page, vma, address,
                                                   &mapcount, vm_flags);
                 if (!mapcount)
                         break;
@@ -507,46 +509,47 @@ int page_referenced(struct page *page,
                     unsigned long *vm_flags)
 {
         int referenced = 0;
+        int we_locked = 0;
 
         if (TestClearPageReferenced(page))
                 referenced++;
 
         *vm_flags = 0;
-        if (page_mapped(page) && page->mapping) {
-                if (PageAnon(page))
+        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, mem_cont,
+                                                                vm_flags);
+                else if (PageAnon(page))
                         referenced += page_referenced_anon(page, mem_cont,
                                                                 vm_flags);
-                else if (is_locked)
+                else if (page->mapping)
                         referenced += page_referenced_file(page, mem_cont,
                                                                 vm_flags);
-                else if (!trylock_page(page))
-                        referenced++;
-                else {
-                        if (page->mapping)
-                                referenced += page_referenced_file(page,
-                                                        mem_cont, vm_flags);
+                if (we_locked)
                         unlock_page(page);
-                }
         }
-
+out:
         if (page_test_and_clear_young(page))
                 referenced++;
 
         return referenced;
 }
 
-static int page_mkclean_one(struct page *page, struct vm_area_struct *vma)
+static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
+                            unsigned long address)
 {
         struct mm_struct *mm = vma->vm_mm;
-        unsigned long address;
         pte_t *pte;
         spinlock_t *ptl;
         int ret = 0;
 
-        address = vma_address(page, vma);
-        if (address == -EFAULT)
-                goto out;
-
         pte = page_check_address(page, mm, address, &ptl, 1);
         if (!pte)
                 goto out;
@@ -578,8 +581,12 @@ static int page_mkclean_file(struct address_space *mapping, struct page *page)
 
         spin_lock(&mapping->i_mmap_lock);
         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
-                if (vma->vm_flags & VM_SHARED)
-                        ret += page_mkclean_one(page, vma);
+                if (vma->vm_flags & VM_SHARED) {
+                        unsigned long address = vma_address(page, vma);
+                        if (address == -EFAULT)
+                                continue;
+                        ret += page_mkclean_one(page, vma, address);
+                }
         }
         spin_unlock(&mapping->i_mmap_lock);
         return ret;
@@ -620,14 +627,7 @@ static void __page_set_anon_rmap(struct page *page,
         BUG_ON(!anon_vma);
         anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
         page->mapping = (struct address_space *) anon_vma;
-
         page->index = linear_page_index(vma, address);
-
-        /*
-         * nr_mapped state can be updated without turning off
-         * interrupts because it is not modified via interrupt.
-         */
-        __inc_zone_page_state(page, NR_ANON_PAGES);
 }
 
 /**
@@ -665,14 +665,23 @@ static void __page_check_anon_rmap(struct page *page,
  * @vma:        the vm area in which the mapping is added
  * @address:    the user virtual address mapped
  *
- * The caller needs to hold the pte lock and the page must be locked.
+ * 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)
 {
+        int first = atomic_inc_and_test(&page->_mapcount);
+        if (first)
+                __inc_zone_page_state(page, NR_ANON_PAGES);
+        if (unlikely(PageKsm(page)))
+                return;
+
         VM_BUG_ON(!PageLocked(page));
         VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
-        if (atomic_inc_and_test(&page->_mapcount))
+        if (first)
                 __page_set_anon_rmap(page, vma, address);
         else
                 __page_check_anon_rmap(page, vma, address);
@@ -694,6 +703,7 @@ void page_add_new_anon_rmap(struct page *page,
         VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
         SetPageSwapBacked(page);
         atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
+        __inc_zone_page_state(page, NR_ANON_PAGES);
         __page_set_anon_rmap(page, vma, address);
         if (page_evictable(page, vma))
                 lru_cache_add_lru(page, LRU_ACTIVE_ANON);
@@ -760,20 +770,15 @@ void page_remove_rmap(struct page *page)
  * Subfunctions of try_to_unmap: try_to_unmap_one called
  * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
  */
-static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
-                                enum ttu_flags flags)
+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;
-        unsigned long address;
         pte_t *pte;
         pte_t pteval;
         spinlock_t *ptl;
         int ret = SWAP_AGAIN;
 
-        address = vma_address(page, vma);
-        if (address == -EFAULT)
-                goto out;
-
         pte = page_check_address(page, mm, address, &ptl, 0);
         if (!pte)
                 goto out;
@@ -784,10 +789,11 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
          * skipped over this mm) then we should reactivate it.
          */
         if (!(flags & TTU_IGNORE_MLOCK)) {
-                if (vma->vm_flags & VM_LOCKED) {
-                        ret = SWAP_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)) {
@@ -822,7 +828,11 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                          * Store the swap location in the pte.
                          * See handle_pte_fault() ...
                          */
-                        swap_duplicate(entry);
+                        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))
@@ -849,7 +859,6 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
         } else
                 dec_mm_counter(mm, file_rss);
 
-
         page_remove_rmap(page);
         page_cache_release(page);
 
@@ -857,6 +866,27 @@ out_unmap:
         pte_unmap_unlock(pte, ptl);
 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->lock or mapping->i_mmap_lock.
+         * 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;
 }
 
 /*
@@ -922,11 +952,10 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
                 return ret;
 
         /*
-         * MLOCK_PAGES => feature is configured.
-         * if we can acquire the mmap_sem for read, and vma is VM_LOCKED,
+         * 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 (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) {
+        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 */
@@ -976,29 +1005,11 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
         return ret;
 }
 
-/*
- * common handling for pages mapped in VM_LOCKED vmas
- */
-static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma)
-{
-        int mlocked = 0;
-
-        if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
-                if (vma->vm_flags & VM_LOCKED) {
-                        mlock_vma_page(page);
-                        mlocked++;      /* really mlocked the page */
-                }
-                up_read(&vma->vm_mm->mmap_sem);
-        }
-        return mlocked;
-}
-
 /**
  * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
  * rmap method
  * @page: the page to unmap/unlock
- * @unlock:  request for unlock rather than unmap [unlikely]
- * @migration:  unmapping for migration - ignored if @unlock
+ * @flags: action and flags
  *
  * Find all the mappings of a page using the mapping pointer and the vma chains
  * contained in the anon_vma struct it points to.
@@ -1014,42 +1025,22 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
 {
         struct anon_vma *anon_vma;
         struct vm_area_struct *vma;
-        unsigned int mlocked = 0;
         int ret = SWAP_AGAIN;
-        int unlock = TTU_ACTION(flags) == TTU_MUNLOCK;
-
-        if (MLOCK_PAGES && unlikely(unlock))
-                ret = SWAP_SUCCESS;     /* default for try_to_munlock() */
 
         anon_vma = page_lock_anon_vma(page);
         if (!anon_vma)
                 return ret;
 
         list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
-                if (MLOCK_PAGES && unlikely(unlock)) {
-                        if (!((vma->vm_flags & VM_LOCKED) &&
-                              page_mapped_in_vma(page, vma)))
-                                continue;  /* must visit all unlocked vmas */
-                        ret = SWAP_MLOCK;  /* saw at least one mlocked vma */
-                } else {
-                        ret = try_to_unmap_one(page, vma, flags);
-                        if (ret == SWAP_FAIL || !page_mapped(page))
-                                break;
-                }
-                if (ret == SWAP_MLOCK) {
-                        mlocked = try_to_mlock_page(page, vma);
-                        if (mlocked)
-                                break;  /* stop if actually mlocked page */
-                }
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
+                ret = try_to_unmap_one(page, vma, address, flags);
+                if (ret != SWAP_AGAIN || !page_mapped(page))
+                        break;
         }
 
         page_unlock_anon_vma(anon_vma);
-
-        if (mlocked)
-                ret = SWAP_MLOCK;       /* actually mlocked the page */
-        else if (ret == SWAP_MLOCK)
-                ret = SWAP_AGAIN;       /* saw VM_LOCKED vma */
-
         return ret;
 }
 
@@ -1079,48 +1070,30 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
         unsigned long max_nl_cursor = 0;
         unsigned long max_nl_size = 0;
         unsigned int mapcount;
-        unsigned int mlocked = 0;
-        int unlock = TTU_ACTION(flags) == TTU_MUNLOCK;
-
-        if (MLOCK_PAGES && unlikely(unlock))
-                ret = SWAP_SUCCESS;     /* default for try_to_munlock() */
 
         spin_lock(&mapping->i_mmap_lock);
         vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
-                if (MLOCK_PAGES && unlikely(unlock)) {
-                        if (!((vma->vm_flags & VM_LOCKED) &&
-                                                page_mapped_in_vma(page, vma)))
-                                continue;       /* must visit all vmas */
-                        ret = SWAP_MLOCK;
-                } else {
-                        ret = try_to_unmap_one(page, vma, flags);
-                        if (ret == SWAP_FAIL || !page_mapped(page))
-                                goto out;
-                }
-                if (ret == SWAP_MLOCK) {
-                        mlocked = try_to_mlock_page(page, vma);
-                        if (mlocked)
-                                break;  /* stop if actually mlocked page */
-                }
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
+                ret = try_to_unmap_one(page, vma, address, flags);
+                if (ret != SWAP_AGAIN || !page_mapped(page))
+                        goto out;
         }
 
-        if (mlocked)
+        if (list_empty(&mapping->i_mmap_nonlinear))
                 goto out;
 
-        if (list_empty(&mapping->i_mmap_nonlinear))
+        /*
+         * 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.vm_set.list) {
-                if (MLOCK_PAGES && unlikely(unlock)) {
-                        if (!(vma->vm_flags & VM_LOCKED))
-                                continue;       /* must visit all vmas */
-                        ret = SWAP_MLOCK;       /* leave mlocked == 0 */
-                        goto out;               /* no need to look further */
-                }
-                if (!MLOCK_PAGES && !(flags & TTU_IGNORE_MLOCK) &&
-                        (vma->vm_flags & VM_LOCKED))
-                        continue;
                 cursor = (unsigned long) vma->vm_private_data;
                 if (cursor > max_nl_cursor)
                         max_nl_cursor = cursor;
@@ -1153,16 +1126,12 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
         do {
                 list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
                                                 shared.vm_set.list) {
-                        if (!MLOCK_PAGES && !(flags & TTU_IGNORE_MLOCK) &&
-                            (vma->vm_flags & VM_LOCKED))
-                                continue;
                         cursor = (unsigned long) vma->vm_private_data;
                         while ( cursor < max_nl_cursor &&
                                 cursor < vma->vm_end - vma->vm_start) {
-                                ret = try_to_unmap_cluster(cursor, &mapcount,
-                                                                vma, page);
-                                if (ret == SWAP_MLOCK)
-                                        mlocked = 2;    /* to return below */
+                                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)
@@ -1183,10 +1152,6 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
                 vma->vm_private_data = NULL;
 out:
         spin_unlock(&mapping->i_mmap_lock);
-        if (mlocked)
-                ret = SWAP_MLOCK;       /* actually mlocked the page */
-        else if (ret == SWAP_MLOCK)
-                ret = SWAP_AGAIN;       /* saw VM_LOCKED vma */
         return ret;
 }
 
@@ -1210,7 +1175,9 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
 
         BUG_ON(!PageLocked(page));
 
-        if (PageAnon(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);
@@ -1229,17 +1196,98 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
  *
  * Return values are:
  *
- * SWAP_SUCCESS - no vma's holding page mlocked.
+ * 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)
 {
         VM_BUG_ON(!PageLocked(page) || PageLRU(page));
 
-        if (PageAnon(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);
 }
 
+#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;
+        struct vm_area_struct *vma;
+        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, which also gave the necessary guarantee
+         * (that this anon_vma's slab has not already been destroyed).
+         * This needs to be reviewed later: avoiding page_lock_anon_vma()
+         * is risky, and currently limits the usefulness of rmap_walk().
+         */
+        anon_vma = page_anon_vma(page);
+        if (!anon_vma)
+                return ret;
+        spin_lock(&anon_vma->lock);
+        list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
+                ret = rmap_one(page, vma, address, arg);
+                if (ret != SWAP_AGAIN)
+                        break;
+        }
+        spin_unlock(&anon_vma->lock);
+        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;
+        struct prio_tree_iter iter;
+        int ret = SWAP_AGAIN;
+
+        if (!mapping)
+                return ret;
+        spin_lock(&mapping->i_mmap_lock);
+        vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
+                unsigned long address = vma_address(page, vma);
+                if (address == -EFAULT)
+                        continue;
+                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.
+         */
+        spin_unlock(&mapping->i_mmap_lock);
+        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 */