6 files changed, 80 insertions, 11 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 213d3cf4f5e..640fc229df1 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -737,14 +737,12 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
         if (WARN_ON(PageMlocked(oldpage)))
                 goto out_fallback_unlock;
 
-        remove_from_page_cache(oldpage);
-        page_cache_release(oldpage);
-
-        err = add_to_page_cache_locked(newpage, mapping, index, GFP_KERNEL);
+        err = replace_page_cache_page(oldpage, newpage, GFP_KERNEL);
         if (err) {
-                printk(KERN_WARNING "fuse_try_move_page: failed to add page");
-                goto out_fallback_unlock;
+                unlock_page(newpage);
+                return err;
         }
+
         page_cache_get(newpage);
 
         if (!(buf->flags & PIPE_BUF_FLAG_LRU))
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f512e189be5..a1a1e5384f6 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -96,7 +96,7 @@ extern struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem);
 
 extern int
 mem_cgroup_prepare_migration(struct page *page,
-        struct page *newpage, struct mem_cgroup **ptr);
+        struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask);
 extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
         struct page *oldpage, struct page *newpage, bool migration_ok);
 
@@ -249,7 +249,7 @@ static inline struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *mem)
 
 static inline int
 mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
-        struct mem_cgroup **ptr)
+        struct mem_cgroup **ptr, gfp_t gfp_mask)
 {
         return 0;
 }
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9c66e994540..26946ad483b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -457,6 +457,7 @@ int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
                                 pgoff_t index, gfp_t gfp_mask);
 extern void remove_from_page_cache(struct page *page);
 extern void __remove_from_page_cache(struct page *page);
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);
 
 /*
  * Like add_to_page_cache_locked, but used to add newly allocated pages:
diff --git a/mm/filemap.c b/mm/filemap.c
index 312b6eb7843..c1459f2cdb5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -387,6 +387,76 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 EXPORT_SYMBOL(filemap_write_and_wait_range);
 
 /**
+ * replace_page_cache_page - replace a pagecache page with a new one
+ * @old:        page to be replaced
+ * @new:        page to replace with
+ * @gfp_mask:   allocation mode
+ *
+ * This function replaces a page in the pagecache with a new one.  On
+ * success it acquires the pagecache reference for the new page and
+ * drops it for the old page.  Both the old and new pages must be
+ * locked.  This function does not add the new page to the LRU, the
+ * caller must do that.
+ *
+ * The remove + add is atomic.  The only way this function can fail is
+ * memory allocation failure.
+ */
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
+{
+        int error;
+        struct mem_cgroup *memcg = NULL;
+
+        VM_BUG_ON(!PageLocked(old));
+        VM_BUG_ON(!PageLocked(new));
+        VM_BUG_ON(new->mapping);
+
+        /*
+         * This is not page migration, but prepare_migration and
+         * end_migration does enough work for charge replacement.
+         *
+         * In the longer term we probably want a specialized function
+         * for moving the charge from old to new in a more efficient
+         * manner.
+         */
+        error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask);
+        if (error)
+                return error;
+
+        error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
+        if (!error) {
+                struct address_space *mapping = old->mapping;
+                void (*freepage)(struct page *);
+
+                pgoff_t offset = old->index;
+                freepage = mapping->a_ops->freepage;
+
+                page_cache_get(new);
+                new->mapping = mapping;
+                new->index = offset;
+
+                spin_lock_irq(&mapping->tree_lock);
+                __remove_from_page_cache(old);
+                error = radix_tree_insert(&mapping->page_tree, offset, new);
+                BUG_ON(error);
+                mapping->nrpages++;
+                __inc_zone_page_state(new, NR_FILE_PAGES);
+                if (PageSwapBacked(new))
+                        __inc_zone_page_state(new, NR_SHMEM);
+                spin_unlock_irq(&mapping->tree_lock);
+                radix_tree_preload_end();
+                if (freepage)
+                        freepage(old);
+                page_cache_release(old);
+                mem_cgroup_end_migration(memcg, old, new, true);
+        } else {
+                mem_cgroup_end_migration(memcg, old, new, false);
+        }
+
+        return error;
+}
+EXPORT_SYMBOL_GPL(replace_page_cache_page);
+
+/**
  * add_to_page_cache_locked - add a locked page to the pagecache
  * @page:       page to add
  * @mapping:    the page's address_space
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index da53a252b25..6ef5c53dffc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2883,7 +2883,7 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
  * page belongs to.
  */
 int mem_cgroup_prepare_migration(struct page *page,
-        struct page *newpage, struct mem_cgroup **ptr)
+        struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
 {
         struct page_cgroup *pc;
         struct mem_cgroup *mem = NULL;
@@ -2940,7 +2940,7 @@ int mem_cgroup_prepare_migration(struct page *page,
                 return 0;
 
         *ptr = mem;
-        ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false, PAGE_SIZE);
+        ret = __mem_cgroup_try_charge(NULL, gfp_mask, ptr, false, PAGE_SIZE);
         css_put(&mem->css);/* drop extra refcnt */
         if (ret || *ptr == NULL) {
                 if (PageAnon(page)) {
diff --git a/mm/migrate.c b/mm/migrate.c
index 352de555626..8aacce3af8c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -678,7 +678,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
         }
 
         /* charge against new page */
-        charge = mem_cgroup_prepare_migration(page, newpage, &mem);
+        charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
         if (charge == -ENOMEM) {
                 rc = -ENOMEM;
                 goto unlock;