[Devel,rh7,v2,14/21] ms/mm: memcontrol: catch root bypass in move precharge

Submitted by Andrey Ryabinin on Jan. 12, 2017, 9:47 a.m.


Message ID 20170112094738.7720-14-aryabinin@virtuozzo.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Andrey Ryabinin Jan. 12, 2017, 9:47 a.m.
From: Johannes Weiner <hannes@cmpxchg.org>

When mem_cgroup_try_charge() returns -EINTR, it bypassed the charge to
the root memcg.  But move precharging does not catch this and treats
this case as if no charge had happened, thus leaking a charge against
root.  Because of an old optimization, the root memcg's res_counter is
not actually charged right now, but it's still an imbalance and
subsequent patches will charge the root memcg again.

Catch those bypasses to the root memcg and properly cancel them before
giving up the move.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit 692e7c45d95ad1064b6911800e2cfec7fc0236db)
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
 mm/memcontrol.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Patch hide | download patch | download mbox

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 32533bf..cddfb93 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6738,6 +6738,10 @@  static int mem_cgroup_do_precharge(unsigned long count)
 		mc.precharge += count;
 		return ret;
+	if (ret == -EINTR) {
+		__mem_cgroup_cancel_charge(root_mem_cgroup, count);
+		return ret;
+	}
 	/* Try charges one by one with reclaim */
 	while (count--) {
@@ -6746,8 +6750,11 @@  static int mem_cgroup_do_precharge(unsigned long count)
 		 * In case of failure, any residual charges against
 		 * mc.to will be dropped by mem_cgroup_clear_mc()
-		 * later on.
+		 * later on.  However, cancel any charges that are
+		 * bypassed to root right away or they'll be lost.
+		if (ret == -EINTR)
+			__mem_cgroup_cancel_charge(root_mem_cgroup, 1);
 		if (ret)
 			return ret;