linux-kernel - Re: [PATCH 03/14] mm: Share the anon_vma ref counts between KSM and page migration

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Message-ID: <4BBBCD6F.3050707@redhat.com>
Date:	Tue, 06 Apr 2010 20:10:23 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Mel Gorman <mel@....ul.ie>, Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 03/14] mm: Share the anon_vma ref counts between KSM and
 page migration

On 04/06/2010 08:05 PM, Andrew Morton wrote:
> On Fri,  2 Apr 2010 17:02:37 +0100
> Mel Gorman<mel@....ul.ie>  wrote:

>> +#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
>> +
>> +	/*
>> +	 * The external_refcount is taken by either KSM or page migration
>> +	 * to take a reference to an anon_vma when there is no
>> +	 * guarantee that the vma of page tables will exist for
>> +	 * the duration of the operation. A caller that takes
>> +	 * the reference is responsible for clearing up the
>> +	 * anon_vma if they are the last user on release
>> +	 */
>> +	atomic_t external_refcount;
>>   #endif
>
> hah.

>> +	anonvma_external_refcount_init(anon_vma);
>
> What a mouthful.  Can we do s/external_//g?

For the function, sure.

However, I believe it would be good to keep the variable
inside the anon_vma as "external_refcount", because the
VMAs attached to the anon_vma take a reference by being
on the list (and leave the refcount alone).
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