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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Message-ID: <20100428014434.GM510@random.random>
Date:	Wed, 28 Apr 2010 03:44:34 +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 10:29:28AM +0900, KAMEZAWA Hiroyuki wrote:
> Hmm..Mel's patch 2/3 takes vma->anon_vma->lock in vma_adjust(),
> so this patch clears vma->anon_vma...

yep, it should be safe with patch 2 applied too. And I'm unsure why Mel's
patch locks the anon_vma also when vm_start != start. See the other
email I sent about patch 2.

> I think we can unlock this just after move_page_tables().

Checking this, I can't see where exactly is vma->vm_pgoff adjusted
during the atomic section I protected with the anon_vma->lock?
For a moment it looks like these pages become unmovable.

I guess this is why I thought initially that it was move_page_tables
to adjust the page->index. If it doesn't then the vma->vm_pgoff has to
be moved down of shift >>PAGE_SHIFT and it doesn't seem to be
happening which is an unrelated bug.
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