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Date: Fri, 23 Apr 2010 13:55:19 +0900
Message-ID: <x2i28c262361004222155w354632eq636186639ac445b7@mail.gmail.com>
Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache 
	pages
From: Minchan Kim <minchan.kim@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Mel Gorman <mel@csn.ul.ie>, Andrew Morton <akpm@linux-foundation.org>,
       Andrea Arcangeli <aarcange@redhat.com>, Adam Litke <agl@us.ibm.com>,
       Avi Kivity <avi@redhat.com>, David Rientjes <rientjes@google.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Rik van Riel <riel@redhat.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
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Hi, Christoph.

On Fri, Apr 23, 2010 at 12:14 AM, Christoph Lameter <cl@linux.com> wrote:
> On Thu, 22 Apr 2010, Minchan Kim wrote:
>
>> For further optimization, we can hold vma->adjust_lock if vma_address
>> returns -EFAULT. But I hope we redesigns it without new locking.
>> But I don't have good idea, now. :(
>
> You could make it atomic through the use of RCU.
>
> Create a new vma entry with the changed parameters and then atomically
> switch to the new vma.
> Problem is that you have some list_heads in there.

That's a good idea if we can do _simply_.
That's because there are many confusion anon_vma and vma handling nowadays.
(http://thread.gmane.org/gmane.linux.kernel/969907)
So I hope we solve the problem without rather complicated rcu locking
if it isn't critical path.

-- 
Kind regards,
Minchan Kim
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