linux-kernel - Re: [patch 1/7 -mm] oom: filter tasks not sharing the same cpuset

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Date:	Tue, 16 Feb 2010 18:03:44 +1100
From:	Nick Piggin <npiggin@...e.de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch 1/7 -mm] oom: filter tasks not sharing the same cpuset

On Tue, Feb 16, 2010 at 01:52:02PM +0900, KOSAKI Motohiro wrote:
> But this explanation is irrelevant and meaningless. CPUSET can change
> restricted node dynamically. So, the tsk->mempolicy at oom time doesn't
> represent the place of task's usage memory. plus, OOM_DISABLE can 
> always makes undesirable result. it's not special in this case.
> 
> The fact is, both current and your heuristics have a corner case. it's
> obvious. (I haven't seen corner caseless heuristics). then talking your
> patch's merit doesn't help to merge the patch. The most important thing
> is, we keep no regression. personally, I incline your one. but It doesn't
> mean we can ignore its demerit.

Yes we do need to explain the downside of the patch. It is a
heuristic and we can't call either approach perfect.

The fact is that even if 2 tasks are on completely disjoint
memory policies and never _allocate_ from one another's nodes,
you can still have one task pinning memory of the other task's
node.

Most shared and userspace-pinnable resources (pagecache, vfs
caches and fds files sockes etc) are allocated by first-touch
basically.

I don't see much usage of cpusets and oom killer first hand in
my experience, so I am happy to defer to others when it comes
to heuristics. Just so long as we are all aware of the full
story :)

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