From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Now (-mm queue), SwapCache is handled by memcg.
But Handling migration of swap-cache was wrong.

Fix to call uncharge() after ClearPageSwapCache() as
__delete_from_swap_cache()(swap_state.c) does.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujtsu.com>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff -puN mm/migrate.c~memcg-handle-swap-cache-fix mm/migrate.c
--- a/mm/migrate.c~memcg-handle-swap-cache-fix
+++ a/mm/migrate.c
@@ -358,10 +358,8 @@ static int migrate_page_move_mapping(str
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
 
 	write_unlock_irq(&mapping->tree_lock);
-	if (!PageSwapCache(newpage)) {
+	if (!PageSwapCache(newpage))
 		mem_cgroup_uncharge_cache_page(page);
-	} else
-		mem_cgroup_uncharge_page(page);
 
 	return 0;
 }
@@ -399,7 +397,15 @@ static void migrate_page_copy(struct pag
  	}
 
 #ifdef CONFIG_SWAP
-	ClearPageSwapCache(page);
+	if (PageSwapCache(page)) {
+		ClearPageSwapCache(page);
+		/*
+		 * SwapCache is removed implicitly. Uncharge against swapcache
+		 * should be called after ClearPageSwapCache() because
+		 * mem_cgroup_uncharge_page checks the flag.
+		 */
+		mem_cgroup_uncharge_page(page);
+	}
 #endif
 	ClearPageActive(page);
 	ClearPagePrivate(page);
_