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

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Message-ID: <20151208110653.GA25800@dhcp22.suse.cz>
Date:	Tue, 8 Dec 2015 12:06:53 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, mgorman@...e.de,
	rientjes@...gle.com, riel@...hat.com, hughd@...gle.com,
	oleg@...hat.com, andrea@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH -v2] mm, oom: introduce oom reaper

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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