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

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Date:	Fri, 19 Feb 2010 09:01:44 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>
Subject: Re: [PATCH 03/12] mm: Share the anon_vma ref counts between KSM and
 page migration

On Fri, 19 Feb 2010, Mel Gorman wrote:

> > Nitpick:
> > I think this refcnt has something different characteristics than other
> > usual refcnts. Even when refcnt goes down to 0, anon_vma will not be freed.
> > So, I think some kind of name as temporal_reference_count is better than
> > simple "refcnt". Then, it will be clearer what this refcnt is for.
> >
>
> When I read this in a few years, I'll have no idea what "temporal" is
> referring to. The holder of this account is by a process that does not
> necessarily own the page or its mappings but "remote" has special
> meaning as well. "external_count" ?

We could think about getting rid of RCU for anon_vmas and use the refcount
for everything. Would make the handling consistent with other users but
will have performance implications.

Hugh what do you say about this?

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