[PATCH next] memcg: remove PCG_CACHE page_cgroup flag fix2

[Hugh Dickins]

Add comment to MEM_CGROUP_CHARGE_TYPE_MAPPED case in
__mem_cgroup_uncharge_common().

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
This one incremental to patch already in mm-commits.

 mm/memcontrol.c |    5 +++++
 1 file changed, 5 insertions(+)

--- mm-commits/mm/memcontrol.c	2012-02-28 20:45:43.488100423 -0800
+++ linux/mm/memcontrol.c	2012-02-29 18:21:49.144702180 -0800
@@ -2953,6 +2953,11 @@ __mem_cgroup_uncharge_common(struct page
 
 	switch (ctype) {
 	case MEM_CGROUP_CHARGE_TYPE_MAPPED:
+		/*
+		 * Generally PageAnon tells if it's the anon statistics to be
+		 * updated; but sometimes e.g. mem_cgroup_uncharge_page() is
+		 * used before page reached the stage of being marked PageAnon.
+		 */
 		anon = true;
 		/* fallthrough */
 	case MEM_CGROUP_CHARGE_TYPE_DROP:
--
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