Date: Fri, 23 Apr 2010 08:52:03 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Christoph Lameter <cl@linux.com>
Cc: Mel Gorman <mel@csn.ul.ie>, Minchan Kim <minchan.kim@gmail.com>,
       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
Subject: Re: [PATCH 04/14] mm,migration: Allow the migration of
 PageSwapCache pages
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On Thu, 22 Apr 2010 14:40:46 -0500 (CDT)
Christoph Lameter <cl@linux.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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