Swapping tmpfs loads show absurd wrapped rss and wrong cache in memcg's
memory.stat statistics: __mem_cgroup_uncharge_common() is failing to
distinguish the anon and tmpfs cases.

Mostly we can decide between them by PageAnon, which is reliable once
it has been set; but there are several callers who need to uncharge a
MEM_CGROUP_CHARGE_TYPE_MAPPED page before it was fully initialized,
so allow that case to override the PageAnon decision.

Signed-off-by: Hugh Dickins <hughd@google.com>
---

 mm/memcontrol.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- 3.3-rc5-next/mm/memcontrol.c	2012-02-25 10:06:52.496035568 -0800
+++ linux/mm/memcontrol.c	2012-02-26 10:44:32.146365398 -0800

@@ -2944,13 +2944,16 @@ __mem_cgroup_uncharge_common(struct page
 	if (!PageCgroupUsed(pc))
 		goto unlock_out;
 
+	anon = PageAnon(page);
+
 	switch (ctype) {
 	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
+		anon = true;
+		/* fallthrough */

 	case MEM_CGROUP_CHARGE_TYPE_DROP:
 		/* See mem_cgroup_prepare_migration() */
 		if (page_mapped(page) || PageCgroupMigration(pc))
 			goto unlock_out;
-		anon = true;
 		break;
 	case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
 		if (!PageAnon(page)) {	/* Shared memory */

@@ -2958,10 +2961,8 @@ __mem_cgroup_uncharge_common(struct page
 				goto unlock_out;
 		} else if (page_mapped(page)) /* Anon */
 				goto unlock_out;
-		anon = true;
 		break;
 	default:
-		anon = false;
 		break;
 	}