linux-kernel - Re: [PATCH 03/12] mm: Share the anon_vma ref counts between KSM and page migration

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Message-ID: <20100220092921.GH1445@csn.ul.ie>
Date:	Sat, 20 Feb 2010 09:29:21 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Rik van Riel <riel@...hat.com>
Cc:	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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 03/12] mm: Share the anon_vma ref counts between KSM
	and page migration

On Fri, Feb 19, 2010 at 07:16:13PM -0500, Rik van Riel wrote:
> On 02/19/2010 04:58 PM, Mel Gorman wrote:
>
>> external_refcount is about as good as I can think of to explain what's
>> going on :/
>
> Sounds "good" to me.  Much better than giving the wrong
> impression that this is the only refcount for the anon_vma.
>

Have renamed it so. If/when this all gets merged, I'll look into what's
required to make this a "real" refcount rather than the existing locking
mechanism. I'm very wary though because even with your anon_vma changes to
avoid excessive sharing, a refcount in there that is used in all paths might
become a hotly contended cache line. i.e. it might look nice, but it might
be a performance hit. It needs to be done carefully and as a separate
series.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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