linux-kernel - Re: [PATCH] mm/oom_kill.c: don't kill TASK

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Date:	Fri, 18 Sep 2015 18:24:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Kyle Walker <kwalker@...hat.com>, akpm@...ux-foundation.org,
	mhocko@...e.cz, rientjes@...gle.com, hannes@...xchg.org,
	vdavydov@...allels.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Stanislav Kozina <skozina@...hat.com>
Subject: Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks

On 09/18, Christoph Lameter wrote:
>
> > But yes, such a deadlock is possible. I would really like to see the comments
> > from maintainers. In particular, I seem to recall that someone suggested to
> > try to kill another !TIF_MEMDIE process after timeout, perhaps this is what
> > we should actually do...
>
> Well yes here is a patch that kills another memdie process but there is
> some risk with such an approach of overusing the reserves.

Yes, I understand it is not that simple. And probably this is all I can
understand ;)

> --- linux.orig/mm/oom_kill.c	2015-09-18 10:38:29.601963726 -0500
> +++ linux/mm/oom_kill.c	2015-09-18 10:39:55.911699017 -0500
> @@ -265,8 +265,8 @@ enum oom_scan_t oom_scan_process_thread(
>  	 * Don't allow any other task to have access to the reserves.
>  	 */
>  	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
> -		if (oc->order != -1)
> -			return OOM_SCAN_ABORT;
> +		if (unlikely(frozen(task)))
> +			__thaw_task(task);

To simplify the discussion lets ignore PF_FROZEN, this is another issue.

I am not sure this change is enough, we need to ensure that
select_bad_process() won't pick the same task (or its sub-thread) again.

And perhaps something like

	wait_event_timeout(oom_victims_wait, !oom_victims,
				configurable_timeout);

before select_bad_process() makes sense?

Oleg.

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