linux-kernel - Re: [PATCH 3/3] mm,migration: Remove straggling migration PTEs when page tables are being moved after the VMA has already moved

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Date:	Wed, 28 Apr 2010 03:09:20 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Mel Gorman <mel@....ul.ie>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] mm,migration: Remove straggling migration PTEs
 when page tables are being moved after the VMA has already moved

On Wed, Apr 28, 2010 at 03:05:43AM +0200, Andrea Arcangeli wrote:
> 1) adjusting page->index atomically with the pte updates inside pt
>    lock (while it moves from one pte to another)

actually no need of this at all! of course the dst vma will have
vma->vm_pgoff adjusted instead... never mind. So I don't see a problem
there.

I think this is very special of how exec.c abuses move_page_tables by
passing vma as src and dst, when it obviously cannot be indexed in two
anon-vmas because there's a single vma and a single vma->anon_vma, and
src and dst obviously cannot have two different vm_pgoff again because
there's a single vma and there can't be two different vma->vm_pgoff.

So I'm very hopeful do_mremap is already fully safe...
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