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    SubjectRe: [PATCH] oom: skip frozen tasks
    On Fri 26-08-11 11:53:56, Michal Hocko wrote:
    > On Fri 26-08-11 02:21:42, David Rientjes wrote:
    > > On Fri, 26 Aug 2011, Michal Hocko wrote:
    > >
    > > > Let's give all frozen tasks a bonus (OOM_SCORE_ADJ_MAX/2) so that we do
    > > > not consider them unless really necessary and if we really pick up one
    > > > then thaw its threads before we try to kill it.
    > > >
    > >
    > > I don't like arbitrary heuristics like this because they polluted the old
    > > oom killer before it was rewritten and made it much more unpredictable.
    > > The only heuristic it includes right now is a bonus for root tasks so that
    > > when two processes have nearly the same amount of memory usage (within 3%
    > > of available memory), the non-root task is chosen instead.
    > >
    > > This bonus is actually saying that a single frozen task can use up to 50%
    > > more of the machine's capacity in a system-wide oom condition than the
    > > task that will now be killed instead. That seems excessive.
    >
    > Yes, the number is probably too high. I just wanted to start up with
    > something. Maybe we can give it another root bonus. But I agree whatever
    > we use it will be just a random value...
    >
    > >
    > > I do like the idea of automatically thawing the task though and if that's
    > > possible then I don't think we need to manipulate the badness heuristic at
    > > all. I know that wouldn't be feasible when we've frozen _all_ threads and
    >
    > Why it wouldn't be feasible for all threads? If you have all tasks
    > frozen (suspend going on, whole cgroup or all tasks in a cpuset/nodemask
    > are frozen) then the selection is more natural because all of them are
    > equal (with or without a bonus). The bonus tries to reduce thawing if
    > not all of them are frozen.
    > I am not saying the bonus is necessary, though. It depends on what
    > the freezer is used for (e.g. freeze a process which went wild and
    > debug what went wrong wouldn't welcome that somebody killed it or other
    > (mis)use which relies on D state).

    Anyway, I do agree, the two things (bonus and thaw during oom_kill)
    should be handled separately.

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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