linux-kernel - Re: [PATCH 1/2] mm, oom: introduce oom reaper

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Message-Id: <20151216165035.38a4d9b84600d6348a3cf4bf@linux-foundation.org>
Date:	Wed, 16 Dec 2015 16:50:35 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Mel Gorman <mgorman@...e.de>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Argangeli <andrea@...nel.org>,
	Rik van Riel <riel@...hat.com>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 1/2] mm, oom: introduce oom reaper

On Tue, 15 Dec 2015 19:36:15 +0100 Michal Hocko <mhocko@...nel.org> wrote:

> From: Michal Hocko <mhocko@...e.com>
> 
> This is based on the idea from Mel Gorman discussed during LSFMM 2015 and
> independently brought up by Oleg Nesterov.
> 
> The OOM killer currently allows to kill only a single task in a good
> hope that the task will terminate in a reasonable time and frees up its
> memory.  Such a task (oom victim) will get an access to memory reserves
> via mark_oom_victim to allow a forward progress should there be a need
> for additional memory during exit path.
>
> ...
>
> +static void oom_reap_vmas(struct mm_struct *mm)
> +{
> +	int attempts = 0;
> +
> +	while (attempts++ < 10 && !__oom_reap_vmas(mm))
> +		schedule_timeout(HZ/10);

schedule_timeout() in state TASK_RUNNING doesn't do anything.  Use
msleep() or msleep_interruptible().  I can't decide which is more
appropriate - it only affects the load average display.

Which prompts the obvious question: as the no-operativeness of this
call wasn't noticed in testing, why do we have it there...

I guess it means that the __oom_reap_vmas() success rate is nice and
high ;)
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