On Wed 07-11-12 14:10:25, Andrew Morton wrote: > 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. Will do next time. > 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. Yes but it is not _that_ long since fe35004f made it into stable trees (e.g. 3.2.29). The reason why we probably do not see many reports is because people didn't get used to swappiness==0 really works these days - especially with memcg where it means _really_ no swapping. > Realistically, is anyone likely to hurt from this? The primary motivation for the fix was a real report by a customer. -- Michal Hocko SUSE Labs -- 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>