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Date: Wed, 5 May 2010 18:13:19 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
       Minchan Kim <minchan.kim@gmail.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing
 the wrong VMA information
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On Wed, May 05, 2010 at 04:54:54PM +0100, Mel Gorman wrote:
> I'm still thinking of the ordering but one possibility would be to use a mutex

I can't take mutex in split_huge_page... so I'd need to use an other solution.

> Not yet.

Rik's patch that takes the locks in the faster path is preferable to
me, it's just simpler, you know the really "strong" long is the
page->mapping/anon_vma->lock and nothing else. You've a page, you take
that lock, you're done for that very page.

Sure that means updating vm_start/vm_pgoff then requires locking all
anon_vmas that the vma registered into, but that's conceptually
simpler and it doesn't alter the page_lock_anon_vma semantics. Now I
wonder if you said the same_anon_vma is in order, but the same_vma is
not, if it's safe to lock the same_vma in list order in anon_vma_lock,
I didn't experience problems on the anon_vma_chain branch but
anon_vma_lock disables all lockdep lock inversion checking.