linux-kernel - Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

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Date:	Wed, 24 Nov 2010 09:24:39 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, pageexec@...email.hu,
	Solar Designer <solar@...nwall.com>,
	Eugene Teo <eteo@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

Hi

> On 10/25, KOSAKI Motohiro wrote:
> >
> > Because execve() makes new mm struct and setup stack and
> > copy argv. It mean the task have two mm while execve() temporary.
> > Unfortunately this nascent mm is not pointed any tasks, then
> > OOM-killer can't detect this memory usage. therefore OOM-killer
> > may kill incorrect task.
> >
> > Thus, this patch added signal->in_exec_mm member and track
> > nascent mm usage.
> 
> Stupid question.
> 
> Can't we just account these allocations in the old -mm temporary?
> 
> IOW. Please look at the "patch" below. It is of course incomplete
> and wrong (to the point inc_mm_counter() is not safe without
> SPLIT_RSS_COUNTING), and copy_strings/flush_old_exec are not the
> best places to play with mm-counters, just to explain what I mean.
> 
> It is very simple. copy_strings() increments MM_ANONPAGES every
> time we add a new page into bprm->vma. This makes this memory
> visible to select_bad_process().
> 
> When exec changes ->mm (or if it fails), we change MM_ANONPAGES
> counter back.
> 
> Most probably I missed something, but what do you think?

Because, If the pages of argv is swapping out when processing execve,
This accouing doesn't work.

Of cource, changing swapping-out logic is one of way. But I did hope
no VM core logic change. taking implict mlocking argv area during execve
is also one of option. But I did think implicit mlocking is more risky.

Is this enough explanation? Please don't hesitate say "no". If people
don't like my approach, I don't hesitate change my thinking.

Thanks.


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