linux-kernel - Re: [PATCH 3/3 for 2.6.38] oom: oom_kill_process: fix the child

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Date:	Tue, 15 Mar 2011 20:21:45 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Frantisek Hrbata <fhrbata@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3 for 2.6.38] oom: oom_kill_process: fix the
	child_points logic

On 03/14, David Rientjes wrote:
>
> On Mon, 14 Mar 2011, Oleg Nesterov wrote:
>
> > oom_kill_process() starts with victim_points == 0. This means that
> > (most likely) any child has more points and can be killed erroneously.
> >
> > Also, "children has a different mm" doesn't match the reality, we
> > should check child->mm != t->mm. This check is not exactly correct
> > if t->mm == NULL but this doesn't really matter, oom_kill_task()
> > will kill them anyway.
> >
> > Note: "Kill all processes sharing p->mm" in oom_kill_task() is wrong
> > too.
> >
>
> There're two issues you're addressing in this patch.  It only kills a 
> child in place of its selected parent when:
>
>  - the child has a higher badness score, and
>
>  - it has a different ->mm.
>
> In the former case, NACK, we always want to sacrifice children regardless
> of their badness score (as long as it is non-zero) if it has a separate
> ->mm in place of its parent,

Ah. So this was intentional?

OK. I was hypnotized by the security implications, and this looked so
"obviously wrong" to me.

But, of course I can't judge when it comes to oom's heuristic, and you
certainly know better.

So, thanks for correcting me.


Just a question... what about oom_kill_allocating_task? Probably
Documentation/sysctl/vm.txt should be updated.

Oleg.

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