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    SubjectRe: [PATCH] memcg: oom: fix totalpages calculation for memory.swappiness==0
    On Thu, Oct 11, 2012 at 10:57:39AM +0200, Michal Hocko 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@suse.cz>
    > Acked-by: David Rientjes <rientjes@google.com>
    > Cc: stable [3.5+]

    I also don't think it's hackish, the limit depends very much on
    whether reclaim can swap, so it's natural that swappiness shows up
    here.

    Acked-by: Johannes Weiner <hannes@cmpxchg.org>


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