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

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Message-Id: <20100216092311.86bceb0c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 16 Feb 2010 09:23:11 +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 Mon, 15 Feb 2010 16:14:22 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> On Tue, 16 Feb 2010, KAMEZAWA Hiroyuki wrote:
> 
> > > If /proc/sys/vm/panic_on_oom is set to 2, the kernel will panic
> > > regardless of whether the memory allocation is constrained by either a
> > > mempolicy or cpuset.
> > > 
> > > Since mempolicy-constrained out of memory conditions now iterate through
> > > the tasklist and select a task to kill, it is possible to panic the
> > > machine if all tasks sharing the same mempolicy nodes (including those
> > > with default policy, they may allocate anywhere) or cpuset mems have
> > > /proc/pid/oom_adj values of OOM_DISABLE.  This is functionally equivalent
> > > to the compulsory panic_on_oom setting of 2, so the mode is removed.
> > > 
> > > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > 
> > NACK. In an enviroment which depends on cluster-fail-over, this is useful
> > even if in such situation.
> > 
> 
> You don't understand that the behavior has changed ever since 
> mempolicy-constrained oom conditions are now affected by a compulsory 
> panic_on_oom mode, please see the patch description.  It's absolutely 
> insane for a single sysctl mode to panic the machine anytime a cpuset or 
> mempolicy runs out of memory and is more prone to user error from setting 
> it without fully understanding the ramifications than any use it will ever 
> do.  The kernel already provides a mechanism for doing this, OOM_DISABLE.  
> if you want your cpuset or mempolicy to risk panicking the machine, set 
> all tasks that share its mems or nodes, respectively, to OOM_DISABLE.  
> This is no different from the memory controller being immune to such 
> panic_on_oom conditions, stop believing that it is the only mechanism used 
> in the kernel to do memory isolation.
> 
You don't explain why "we _have to_ remove API which is used"

Thanks,
-Kame



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