Message-ID: <467A7C88.2040102@csn.ul.ie>
Date: Thu, 21 Jun 2007 14:26:32 +0100
From: Mel Gorman <mel@csn.ul.ie>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       kamezawa.hiroyu@jp.fujitsu.com, clameter@sgi.com
Subject: Re: [PATCH 7/7] Compact memory directly by a process when a high-order
 allocation fails
References: <20070618092821.7790.52015.sendpatchset@skynet.skynet.ie>	<20070618093042.7790.30669.sendpatchset@skynet.skynet.ie> <20070621052813.ac93e12e.akpm@linux-foundation.org>
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Andrew Morton wrote:
>> On Mon, 18 Jun 2007 10:30:42 +0100 (IST) Mel Gorman <mel@csn.ul.ie> wrote:
>> +
>> +			/*
>> +			 * It's a race if compaction frees a suitable page but
>> +			 * someone else allocates it
>> +			 */
>> +			count_vm_event(COMPACTRACE);
>> +		}
> 
> Could perhaps cause arbitrarily long starvation. 

More likely it will just fail allocations where it could have succeeded.
I knew the situation would occur so I thought I would count how often it
happens before doing.

> A fix would be to free
> the synchronously-compacted higher-order page into somewhere which is
> private to this task (a new field in task_struct would be one such place).

There used to be such fields and a process flag PF_FREE_PAGES for a
similar purpose. I'll look into reintroducing it. Thanks

-- 
Mel Gorman
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