linux-kernel - Re: [PATCH 0/9] oom reaper v6

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Message-ID: <20160323120716.GE7059@dhcp22.suse.cz>
Date:	Wed, 23 Mar 2016 13:07:16 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	rientjes@...gle.com, akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, hannes@...xchg.org,
	mgorman@...e.de, oleg@...hat.com, a.p.zijlstra@...llo.nl,
	vdavydov@...tuozzo.com
Subject: Re: [PATCH 0/9] oom reaper v6

On Wed 23-03-16 20:11:35, Tetsuo Handa wrote:
> David Rientjes wrote:
[...]
> > Tetsuo, have you been able to run your previous test cases on top of this 
> > version and do you have any concerns about it or possible extensions that 
> > could be made?
> > 
> 
> I think [PATCH 3/9] [PATCH 4/9] [PATCH 8/9] will be mostly reverted.
> My concerns and possible extensions are explained in
> 
>     Re: [PATCH 6/5] oom, oom_reaper: disable oom_reaper for oom_kill_allocating_task
>     http://lkml.kernel.org/r/201603152015.JAE86937.VFOLtQFOFJOSHM@I-love.SAKURA.ne.jp

I believe issues you have raised there are a matter for further
discussion as they are potential improvements of the existing
functionality rather than fixing a regression of the current code.

> . Regarding "[PATCH 4/9] mm, oom_reaper: report success/failure",
> debug_show_all_locks() may not be safe
> 
>     commit 856848737bd944c1 "lockdep: fix debug_show_all_locks()"
>     commit 82a1fcb90287052a "softlockup: automatically detect hung TASK_UNINTERRUPTIBLE tasks"

Let me ask again. What exactly is unsafe about calling
debug_show_all_locks here? It is true that 856848737bd944c1 has
changed debug_show_all_locks to ignore running tasks which limits
this functionality to some degree but I still think this might be
useful. Proposed alternatives were way too verbose and complex on its
own. This is something to be further discussed as well, though.

> and showing traces might be more useful.
> (A discussion for making printk() completely async is in progress.)
> 
> But we don't have time to update this series before merge window for 4.6 closes.
> We want to send current patchset as is for now, don't we? So, please go ahead.

I am happy that we are on the same patch here.

> My other concerns about OOM handling:

Let's stick to oom reaper here, please.

Thanks!
-- 
Michal Hocko
SUSE Labs