mm: add replace_page_cache_page() function

This function basically does:

     remove_from_page_cache(old);
     page_cache_release(old);
     add_to_page_cache_locked(new);

Except it does this atomically, so there's no possibility for the "add" to
fail because of a race.

If memory cgroups are enabled, then the memory cgroup charge is also moved
from the old page to the new.

This function is currently used by fuse to move pages into the page cache
on read, instead of copying the page contents.

[minchan.kim@gmail.com: add freepage() hook to replace_page_cache_page()]
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f512e189be5a..a1a1e5384f6e 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 9c66e994540f..26946ad483bf 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: