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

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Message-ID: <20100402191414.GA982@redhat.com>
Date:	Fri, 2 Apr 2010 21:14:14 +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 04/02, David Rientjes wrote:
>
> On Fri, 2 Apr 2010, Oleg Nesterov wrote:
>
> > David, you continue to ignore my arguments ;) select_bad_process()
> > must not filter out the tasks with ->mm == NULL.
> >
> I'm not ignoring your arguments, I think you're ignoring what I'm
> responding to.

Ah, sorry, I misunderstood your replies.

> I prefer to keep oom_badness() to be a positive range as
> it always has been (and /proc/pid/oom_score has always used an unsigned
> qualifier),

Yes, I thought about /proc/pid/oom_score, but imho this is minor issue.
We can s/%lu/%ld/ though, or just report 0 if oom_badness() returns -1.
Or something.

> so I disagree that we need to change oom_badness() to return
> anything other than 0 for such tasks.  We need to filter them explicitly
> in select_bad_process() instead, so please do this there.

The problem is, we need task_lock() to pin ->mm. Or, we can change
find_lock_task_mm() to do get_task_mm() and return mm_struct *.

But then oom_badness() (and proc_oom_score!) needs much more changes,
it needs the new "struct mm_struct *mm" argument which is not necessarily
equal to p->mm.

So, I can't agree.

Oleg.

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