1 files changed, 70 insertions, 0 deletions

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