linux-kernel - Re: [PATCH 04/14] mm,migration: Allow the migration of PageSwapCache pages

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Date:	Fri, 23 Apr 2010 08:52:03 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Mel Gorman <mel@....ul.ie>, Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of
 PageSwapCache pages

On Thu, 22 Apr 2010 14:40:46 -0500 (CDT)
Christoph Lameter <cl@...ux.com> wrote:

> On Thu, 22 Apr 2010, Mel Gorman wrote:
> 
> > vma_adjust() is updating anon VMA information without any locks taken.
> > In constract, file-backed mappings use the i_mmap_lock. This lack of
> > locking can result in races with page migration. During rmap_walk(),
> > vma_address() can return -EFAULT for an address that will soon be valid.
> > This leaves a dangling migration PTE behind which can later cause a
> > BUG_ON to trigger when the page is faulted in.
> 
> Isnt this also a race with reclaim /  swap?
> 
Yes, it's also race in reclaim/swap ...
  page_referenced()
  try_to_unmap().
  rmap_walk()  <==== we hit this case.

But above 2 are not considered to be critical.

I'm not sure how this race affect KSM.

Thanks,
-Kame

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