On Tue, 16 Oct 2012 00:04:08 +0200 Michal Hocko <mhocko@xxxxxxx> wrote: > As Kosaki correctly pointed out, the glogal reclaim doesn't have this > issue because we _do_ swap on swappinnes==0 so the swap space has > to be considered. So the v2 is just acks + changelog fix. > > Changes since v1 > - drop a note about global swappiness affected as well from the > changelog > - stable needs 3.2+ rather than 3.5+ because the fe35004f has been > backported to stable > --- > >From c2ae4849f09dbfda6b61472c6dd1fd8c2fe8ac81 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxx> > Date: Wed, 10 Oct 2012 15:46:54 +0200 > Subject: [PATCH] memcg: oom: fix totalpages calculation for > memory.swappiness==0 > > oom_badness takes 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 fe35004f (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@xxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: stable [3.2+] That's "Cc: <stable@xxxxxxxxxxxxxxx>", please. It's unobvious from the changelog that a -stable backport is really needed. The bug looks pretty obscure and has been there for a long time. Realistically, is anyone likely to hurt from this? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>