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 16:42:18 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
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 02/18/2010 01:02 PM, Mel Gorman wrote:

>   struct anon_vma {
>   	spinlock_t lock;	/* Serialize access to vma list */
> -#ifdef CONFIG_KSM
> -	atomic_t ksm_refcount;
> -#endif
> -#ifdef CONFIG_MIGRATION
> -	atomic_t migrate_refcount;
> +#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
> +
> +	/*
> +	 * The 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 refcount;

Calling it just refcount is probably confusing, since
the anon_vma is also referenced by being on the chain
with others.

Maybe "other_refcount" because it is refcounts taken
by things other than VMAs?  I am sure there is a better
name possible...

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