linux-kernel - Re: [patch v4] mm, oom: fix unnecessary killing of additional processes

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Message-ID: <alpine.DEB.2.21.1807241444370.206335@chino.kir.corp.google.com>
Date:   Tue, 24 Jul 2018 14:45:58 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch v4] mm, oom: fix unnecessary killing of additional
 processes

On Sat, 21 Jul 2018, Tetsuo Handa wrote:

> You can't apply "[patch v4] mm, oom: fix unnecessary killing of additional processes"
> because Michal's patch which removes oom_lock serialization was added to -mm tree.
> 

I've rebased the patch to linux-next and posted a v5.

> You might worry about situations where __oom_reap_task_mm() is a no-op.
> But that is not always true. There is no point with emitting
> 
>   pr_info("oom_reaper: unable to reap pid:%d (%s)\n", ...);
>   debug_show_all_locks();
> 
> noise and doing
> 
>   set_bit(MMF_OOM_SKIP, &mm->flags);
> 
> because exit_mmap() will not release oom_lock until __oom_reap_task_mm()
> completes. That is, except extra noise, there is no difference with
> current behavior which sets set_bit(MMF_OOM_SKIP, &mm->flags) after
> returning from __oom_reap_task_mm().
> 

v5 has restructured how exit_mmap() serializes its unmapping with the oom 
reaper.  It sets MMF_OOM_SKIP while holding mm->mmap_sem.