linux-kernel - Re: [PATCH 09/10] mm, oom_reaper: do not attempt to reap a task more than twice

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Date:	Wed, 15 Jun 2016 16:48:35 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-mm@...ck.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 09/10] mm, oom_reaper: do not attempt to reap a task more
 than twice

On 06/09, Michal Hocko wrote:
>
> @@ -556,8 +556,27 @@ static void oom_reap_task(struct task_struct *tsk)
>  		schedule_timeout_idle(HZ/10);
>  
>  	if (attempts > MAX_OOM_REAP_RETRIES) {
> +		struct task_struct *p;
> +
>  		pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
>  				task_pid_nr(tsk), tsk->comm);
> +
> +		/*
> +		 * If we've already tried to reap this task in the past and
> +		 * failed it probably doesn't make much sense to try yet again
> +		 * so hide the mm from the oom killer so that it can move on
> +		 * to another task with a different mm struct.
> +		 */
> +		p = find_lock_task_mm(tsk);
> +		if (p) {
> +			if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {
> +				pr_info("oom_reaper: giving up pid:%d (%s)\n",
> +						task_pid_nr(tsk), tsk->comm);
> +				set_bit(MMF_OOM_REAPED, &p->mm->flags);

But why do we need MMF_OOM_NOT_REAPABLE? We set MMF_OOM_REAPED, oom_reap_task()
should not see this task again, at least too often.

Oleg.