Re: [RFC PATCH -v2] mm, oom: introduce oom reaper

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH -v2] mm, oom: introduce oom reaper
Date	2015-12-08 12:10 +0100
Message-ID	<qDojE-1AO-11@gated-at.bofh.it> (permalink)
References	(1 earlier) <qzQo9-2Ef-3@gated-at.bofh.it> <qATjY-1Oq-25@gated-at.bofh.it> <qCki5-12G-1@gated-at.bofh.it> <qD6ws-6Nn-63@gated-at.bofh.it> <qDciu-2cp-31@gated-at.bofh.it>
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On Tue 08-12-15 07:19:42, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > Yes you are right! The reference count should be incremented before
> > publishing the new mm_to_reap. I thought that an elevated ref. count by
> > the caller would be enough but this was clearly wrong. Does the update
> > below looks better?
> 
> I think that moving mmdrop() from oom_kill_process() to
> oom_reap_vmas() xor wake_oom_reaper() makes the patch simpler.

It surely is less lines of code but I am not sure it is simpler. I do
not think we should drop the reference in a different path than it is
taken.  Maybe we will grow more users of wake_oom_reaper in the future
and this is quite subtle behavior.

> 
>  	rcu_read_unlock();
>  
> +	if (can_oom_reap)
> +		wake_oom_reaper(mm); /* will call mmdrop() */
> +	else
> +		mmdrop(mm);
> -	mmdrop(mm);
>  	put_task_struct(victim);
>  }

Thanks!
-- 
Michal Hocko
SUSE Labs
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Re: [RFC PATCH -v2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-01 14:40 +0100
  Re: [RFC PATCH -v2] mm, oom: introduce oom reaper Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-05 13:40 +0100
    Re: [RFC PATCH -v2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-07 17:10 +0100
      Re: [RFC PATCH -v2] mm, oom: introduce oom reaper Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2015-12-07 23:20 +0100
        Re: [RFC PATCH -v2] mm, oom: introduce oom reaper Michal Hocko <mhocko@kernel.org> - 2015-12-08 12:10 +0100

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