memcg: fix memory.high target
authorVladimir Davydov <vdavydov@virtuozzo.com>
Fri, 11 Dec 2015 21:40:24 +0000 (13:40 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 12 Dec 2015 18:15:34 +0000 (10:15 -0800)
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@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memcontrol.c

index c92a65b2b4ab4103454aa1f8bca828384b22e07b..32259e37a66baf54ccf19f104b915d642d6c3828 100644 (file)
@@ -2128,7 +2128,7 @@ 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;
                }