linux-kernel - Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on

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Message-Id: <20100217090124.398769d5.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 17 Feb 2010 09:01:24 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on_oom mode

On Tue, 16 Feb 2010 15:54:50 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 17 Feb 2010, KAMEZAWA Hiroyuki wrote:
> > Then, please leave panic_on_oom=always.
> > Even with mempolicy or cpuset 's OOM, we need panic_on_oom=always option.
> > And yes, I'll add something similar to memcg. freeze_at_oom or something.
> > 
> 
> Memcg isn't a special case here, it should also panic the machine if 
> panic_on_oom == 2, so if we aren't going to remove this option then I 
> agree with Nick that we need to panic from mem_cgroup_out_of_memory() as 
> well.  Some users use cpusets, for example, for the same effect of memory 
> isolation as you use memcg, so panicking in one scenario and not the other 
> is inconsistent.
> 
Hmm, I have a few reason to add special behavior to memcg rather than panic.

 - freeze_at_oom is enough.
   If OOM can be notified, the management daemon can do useful jobs. Shutdown
   all other cgroups or migrate them to other host and do kdump.

 - memcg's oom is not very complicated.
   Because we just counts RSS+FileCache

But, Hmm...I'd like to go this way.

 1. At first, support panic_on_oom=2 in memcg.

 2. Second, I'll add OOM-notifier and freeze_at_oom to memcg.
    and don't call memcg_out_of_memory in oom_kill.c in this case. Because
    we don't kill anything. Taking coredumps of all procs in memcg is not
    very difficult.

I need to discuss with memcg guys. But this will be a way to go, I think

Thanks,
-Kame

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