linux-kernel - Re: [PATCH 4/5] always lock the root (oldest) anon

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Message-ID: <20100527135356.GD2112@barrios-desktop>
Date:	Thu, 27 May 2010 22:55:07 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Mel Gorman <mel@....ul.ie>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: [PATCH 4/5] always lock the root (oldest) anon_vma

On Wed, May 26, 2010 at 03:40:44PM -0400, Rik van Riel wrote:
> Subject: always lock the root (oldest) anon_vma
> 
> Always (and only) lock the root (oldest) anon_vma whenever we do something in an
> anon_vma.  The recently introduced anon_vma scalability is due to the rmap code
> scanning only the VMAs that need to be scanned.  Many common operations still
> took the anon_vma lock on the root anon_vma, so always taking that lock is not
> expected to introduce any scalability issues.
> 
> However, always taking the same lock does mean we only need to take one lock,
> which means rmap_walk on pages from any anon_vma in the vma is excluded from
> occurring during an munmap, expand_stack or other operation that needs to
> exclude rmap_walk and similar functions.
> 
> Also add the proper locking to vma_adjust.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

Nitpick:

It would be better to modify comment about head of anon_vma in rmap.h, too.
/*  
 * NOTE: the LSB of the head.next is set by
                   ->   root->hext.next 
-- 
Kind regards,
Minchan Kim
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