path: root/Documentation/cgroups
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authorMichal Hocko <mhocko@suse.cz>2012-11-16 14:14:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-11-16 14:33:04 -0800
commit9a5a8f19b43430752067ecaee62fc59e11e88fa6 (patch)
treeffa31761b0e208d8be324dc97368caf4bea87fd8 /Documentation/cgroups
parent1756954c61cb5c97c618ccb366482b9c1f891d6d (diff)
memcg: oom: fix totalpages calculation for memory.swappiness==0
oom_badness() takes a totalpages argument which says how many pages are available and it uses it as a base for the score calculation. The value is calculated by mem_cgroup_get_limit which considers both limit and total_swap_pages (resp. memsw portion of it). This is usually correct but since fe35004fbf9e ("mm: avoid swapping out with swappiness==0") we do not swap when swappiness is 0 which means that we cannot really use up all the totalpages pages. This in turn confuses oom score calculation if the memcg limit is much smaller than the available swap because the used memory (capped by the limit) is negligible comparing to totalpages so the resulting score is too small if adj!=0 (typically task with CAP_SYS_ADMIN or non zero oom_score_adj). A wrong process might be selected as result. The problem can be worked around by checking mem_cgroup_swappiness==0 and not considering swap at all in such a case. Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/cgroups')
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index c07f7b4fb88..71c4da41344 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -466,6 +466,10 @@ Note:
5.3 swappiness
Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
+Please note that unlike the global swappiness, memcg knob set to 0
+really prevents from any swapping even if there is a swap storage
+available. This might lead to memcg OOM killer if there are no file
+pages to reclaim.
Following cgroups' swappiness can't be changed.
- root cgroup (uses /proc/sys/vm/swappiness).