linux-kernel - Re: [PATCH 07/28] extend KSM refcounts to the anon

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Message-ID: <20100609105518.GC5650@csn.ul.ie>
Date:	Wed, 9 Jun 2010 11:55:18 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Nick Piggin <npiggin@...e.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 07/28] extend KSM refcounts to the anon_vma root

On Mon, Jun 07, 2010 at 01:07:01PM +0200, Peter Zijlstra wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> KSM reference counts can cause an anon_vma to exist after the processe
> it belongs to have already exited.  Because the anon_vma lock now lives
> in the root anon_vma, we need to ensure that the root anon_vma stays
> around until after all the "child" anon_vmas have been freed.
> 
> The obvious way to do this is to have a "child" anon_vma take a
> reference to the root in anon_vma_fork.  When the anon_vma is freed
> at munmap or process exit, we drop the refcount in anon_vma_unlink
> and possibly free the root anon_vma.
> 
> The KSM anon_vma reference count function also needs to be modified
> to deal with the possibility of freeing 2 levels of anon_vma.  The
> easiest way to do this is to break out the KSM magic and make it
> generic.
> 
> When compiling without CONFIG_KSM, this code is compiled out.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <20100526154124.04607d04@...uminas.surriel.com>

Acked-by: Mel Gorman <mel@....ul.ie

> <SNIP>

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