Re: [PATCH] memcg: oom: fix totalpages calculation formemory.swappiness==0

[Michal Hocko]

On Thu 11-10-12 18:36:26, KOSAKI Motohiro wrote:
> On Thu, Oct 11, 2012 at 4:57 AM, Michal Hocko <mhocko@xxxxxxx> wrote:
> > 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 same issue exists for the global oom killer as well but it is not
> > that problematic as the amount of the RAM is usually much bigger than
> > the swap space.
> >
> > 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>
> > Cc: stable [3.5+]
> 
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>

Thanks!

-- 
Michal Hocko
SUSE Labs
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