The patch titled
memcg: add comments explaining memory barriers
has been added to the -mm tree. Its filename is
memcg-add-comments-explaining-memory-barriers.patch
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------------------------------------------------------
Subject: memcg: add comments explaining memory barriers
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Add comments for the reason of smp_wmb() in mem_cgroup_commit_charge().
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN mm/memcontrol.c~memcg-add-comments-explaining-memory-barriers mm/memcontrol.c
--- a/mm/memcontrol.c~memcg-add-comments-explaining-memory-barriers
+++ a/mm/memcontrol.c
@@ -1134,6 +1134,13 @@ static void __mem_cgroup_commit_charge(s
}
pc->mem_cgroup = mem;
+ /*
+ * We access a page_cgroup asynchronously without lock_page_cgroup().
+ * Especially when a page_cgroup is taken from a page, pc->mem_cgroup
+ * is accessed after testing USED bit. To make pc->mem_cgroup visible
+ * before USED bit, we need memory barrier here.
+ * See mem_cgroup_add_lru_list(), etc.
+ */
smp_wmb();
switch (ctype) {
case MEM_CGROUP_CHARGE_TYPE_CACHE:
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
elf-limit-max-map-count-to-safe-value.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup-fix.patch
memcg-add-comments-explaining-memory-barriers.patch
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