linux-kernel - Re: [patch] oom: give current access to memory reserves if it has been killed

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Date:	Thu, 1 Apr 2010 16:00:11 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] oom: give current access to memory reserves if it has
	been killed

On 04/01, David Rientjes wrote:
>
> On Wed, 31 Mar 2010, Oleg Nesterov wrote:
>
> > Probably something like the patch below makes sense. Note that
> > "skip kernel threads" logic is wrong too, we should check PF_KTHREAD.
> > Probably it is better to check it in select_bad_process() instead,
> > near is_global_init().
>
> is_global_init() will be true for p->flags & PF_KTHREAD.

No, is_global_init() && PF_KTHREAD have nothing to do with each other.

> > @@ -159,13 +172,9 @@ unsigned int oom_badness(struct task_str
> >  	if (p->flags & PF_OOM_ORIGIN)
> >  		return 1000;
> >
> > -	task_lock(p);
> > -	mm = p->mm;
> > -	if (!mm) {
> > -		task_unlock(p);
> > +	p = find_lock_task_mm(p);
> > +	if (!p)
> >  		return 0;
> > -	}
> > -
> >  	/*
> >  	 * The baseline for the badness score is the proportion of RAM that each
> >  	 * task's rss and swap space use.
> > @@ -330,12 +339,6 @@ static struct task_struct *select_bad_pr
> >  			*ppoints = 1000;
> >  		}
> >
> > -		/*
> > -		 * skip kernel threads and tasks which have already released
> > -		 * their mm.
> > -		 */
> > -		if (!p->mm)
> > -			continue;
> >  		if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
> >  			continue;
>
> You can't do this for the reason I cited in another email, oom_badness()
> returning 0 does not exclude a task from being chosen by
> selcet_bad_process(), it will use that task if nothing else has been found
> yet.  We must explicitly filter it from consideration by checking for
> !p->mm.

Yes, you are right. OK, oom_badness() can never return points < 0,
we can make it int and oom_badness() can return -1 if !mm. IOW,

	- unsigned int points;
	+ int points;
	...

	points = oom_badness(...);
	if (points >= 0 && (points > *ppoints || !chosen))
		chosen = p;

Oleg.

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