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

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Date:	Tue, 16 Feb 2010 18:28:05 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Wed, 17 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > What do you think about making pagefaults use out_of_memory() directly and 
> > respecting the sysctl_panic_on_oom settings?
> > 
> 
> I don't think this patch is good. Because several memcg can
> cause oom at the same time independently, system-wide oom locking is
> unsuitable. BTW, what I doubt is much more fundamental thing.
> 

We want to lock all populated zones with ZONE_OOM_LOCKED to avoid 
needlessly killing more than one task regardless of how many memcgs are 
oom.

> What I doubt at most is "why VM_FAULT_OOM is necessary ? or why we have
> to call oom_killer when page fault returns it".
> Is there someone who returns VM_FAULT_OOM without calling page allocator
> and oom-killer helps something in such situation ?
> 

Before we invoked the oom killer for VM_FAULT_OOM, we simply sent a 
SIGKILL to current because we simply don't have memory to fault the page 
in, it's better to select a memory-hogging task to kill based on badness() 
than to constantly kill current which may not help in the long term.
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