linux-kernel - [PATCH] memcg: fix memory.high target

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Date:	Mon, 23 Nov 2015 15:22:31 +0300
From:	Vladimir Davydov <vdavydov@...tuozzo.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>, Tejun Heo <tj@...nel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] memcg: fix memory.high target

When the memory.high threshold is exceeded, try_charge() schedules a
task_work to reclaim the excess. The reclaim target is set to the number
of pages requested by try_charge(). This is wrong, because try_charge()
usually charges more pages than requested (batch > nr_pages) in order to
refill per cpu stocks. As a result, a process in a cgroup can easily
exceed memory.high significantly when doing a lot of charges w/o
returning to userspace (e.g. reading a file in big chunks).

Fix this issue by assuring that when exceeding memory.high a process
reclaims as many pages as were actually charged (i.e. batch).

Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 648cc9f02437..06c476ab0f2c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2133,7 +2133,7 @@ done_restock:
 	 */
 	do {
 		if (page_counter_read(&memcg->memory) > memcg->high) {
-			current->memcg_nr_pages_over_high += nr_pages;
+			current->memcg_nr_pages_over_high += batch;
 			set_notify_resume(current);
 			break;
 		}
-- 
2.1.4

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