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

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Date:	Tue, 16 Feb 2010 01:10:44 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Nick Piggin <npiggin@...e.de>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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, 16 Feb 2010, Nick Piggin wrote:

> I don't really agree with your black and white view. We equally
> can't tell a lot of cases about who is pinning memory where. The
> fact is that any task can be pinning memory and the heuristic
> was specifically catering for that.
> 

That's a main source of criticism of the current heuristic: it needlessly 
kills tasks.  There is only one thing we know for certain: current is 
trying to allocate memory on its nodes.  We can either kill a task that 
is allowed that same set or current itself; there's no evidence that 
killing anything else will lead to memory freeing that will allow the 
allocation to succeed.  The heuristic will never perfectly select the task 
that it should kill 100% of the time when playing around with mempolicy 
nodes or cpuset mems, but relying on their current placement is a good 
indicator of what is more likely than not to free memory of interest.
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