On Mon, Jul 09, 2012 at 11:42:12AM +0900, Kamezawa Hiroyuki wrote:

(2012/07/05 9:44), Johannes Weiner wrote:

quoted

@@ -3278,10 +3283,11 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
  		unused = oldpage;
  	}
  	anon = PageAnon(used);
-	__mem_cgroup_uncharge_common(unused,
-		anon ? MEM_CGROUP_CHARGE_TYPE_ANON
-		     : MEM_CGROUP_CHARGE_TYPE_CACHE,
-		true);
+	if (!PageSwapCache(page))
+		__mem_cgroup_uncharge_common(unused,
+					     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
+					     : MEM_CGROUP_CHARGE_TYPE_CACHE,
+					     true);

!PageSwapCache(unused) ?

Argh, right.

But I think unused page's PG_swapcache is always dropped. So, the check is
not necessary.

Oh, this is intentional: the check was in __mem_cgroup_uncharge_common
before, which means it applied to this entry point as well.  This is
supposed to be a mechanical change that does not change any logic.
The check is then removed in the next patch.

---
Subject: mm: memcg: push down PageSwapCache check into uncharge entry functions fix

Signed-off-by: Johannes Weiner <redacted>
---

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a3bf414..f4ff18a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -3283,7 +3283,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
 		unused = oldpage;
 	}
 	anon = PageAnon(used);
-	if (!PageSwapCache(page))
+	if (!PageSwapCache(unused))
 		__mem_cgroup_uncharge_common(unused,
 					     anon ? MEM_CGROUP_CHARGE_TYPE_ANON
 					     : MEM_CGROUP_CHARGE_TYPE_CACHE,