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

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Message-ID: <20100331233058.GA6081@redhat.com>
Date:	Thu, 1 Apr 2010 01:30:58 +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, Oleg Nesterov wrote:
>
> On 03/31, David Rientjes wrote:
> >
> > On Wed, 31 Mar 2010, Oleg Nesterov wrote:
> >
> > > On 03/30, David Rientjes wrote:
> > > >
> > > > On Tue, 30 Mar 2010, Oleg Nesterov wrote:
> > > >
> > > > > Note that __oom_kill_task() does force_sig(SIGKILL) which assumes that
> > > > > ->sighand != NULL. This is not true if out_of_memory() is called after
> > > > > current has already passed exit_notify().
> > > >
> > > > We have an even bigger problem if current is in the oom killer at
> > > > exit_notify() since it has already detached its ->mm in exit_mm() :)
> > >
> > > Can't understand... I thought that in theory even kmalloc(1) can trigger
> > > oom.
> >
> > __oom_kill_task() cannot be called on a task without an ->mm.
>
> Why? You ignored this part:
>
> 	Say, right after exit_mm() we are doing acct_process(), and f_op->write()
> 	needs a page. So, you are saying that in this case __page_cache_alloc()
> 	can never trigger out_of_memory() ?
>
> why this is not possible?
>
> David, I am not arguing, I am asking.

In case I wasn't clear...

Yes, currently __oom_kill_task(p) is not possible if p->mm == NULL.

But your patch adds

	if (fatal_signal_pending(current))
		__oom_kill_task(current);

into out_of_memory().

Oleg.

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