linux-kernel - Re: [RFC 1/2] mm: oom: expose expedite_reclaim to use oom_reaper outside of oom

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Date:   Thu, 25 Apr 2019 14:56:16 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        yuzhoujian@...ichuxing.com,
        Souptick Joarder <jrdr.linux@...il.com>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Minchan Kim <minchan@...nel.org>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>, linux-mm <linux-mm@...ck.org>,
        lsf-pc@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [RFC 1/2] mm: oom: expose expedite_reclaim to use oom_reaper
 outside of oom_kill.c

On Thu, Apr 25, 2019 at 2:13 PM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2019/04/11 10:43, Suren Baghdasaryan wrote:
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 3a2484884cfd..6449710c8a06 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -1102,6 +1102,21 @@ bool out_of_memory(struct oom_control *oc)
> >       return !!oc->chosen;
> >  }
> >
> > +bool expedite_reclaim(struct task_struct *task)
> > +{
> > +     bool res = false;
> > +
> > +     task_lock(task);
> > +     if (task_will_free_mem(task)) {
>
> mark_oom_victim() needs to be called under oom_lock mutex after
> checking that oom_killer_disabled == false. Since you are trying
> to trigger this function from signal handler, you might want to
> defer until e.g. WQ context.

Thanks for the tip! I'll take this into account in the new design.
Just thinking out loud... AFAIU oom_lock is there to protect against
multiple concurrent out_of_memory calls from different contexts and
prevent overly-aggressive process killing. For my purposes when
reaping memory of a killed process we don't have this concern (we did
not initiate the killing, SIGKILL was explicitly requested). I'll
probably need some synchronization there but not for purposes of
preventing multiple concurrent reapers. In any case, thank you for the
feedback!

>
> > +             mark_oom_victim(task);
> > +             wake_oom_reaper(task);
> > +             res = true;
> > +     }
> > +     task_unlock(task);
> > +
> > +     return res;
> > +}
> > +
> >  /*
> >   * The pagefault handler calls here because it is out of memory, so kill a
> >   * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
> >