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Date: Fri, 7 May 2010 07:18:39 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
cc: Mel Gorman <mel@csn.ul.ie>, Andrew Morton <akpm@linux-foundation.org>,
       Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
       Minchan Kim <minchan.kim@gmail.com>, Christoph Lameter <cl@linux.com>,
       Andrea Arcangeli <aarcange@redhat.com>, Rik van Riel <riel@redhat.com>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and
 rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary
 stack
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On Fri, 7 May 2010, KAMEZAWA Hiroyuki wrote:
> 
> Hmm, is this too slow ? This is the simplest one I have.

Well, it may be as slow (or slower) than Andrea's, but at least it is 
_clean_ and actually removes code. So if we can't do it better, I'd 
certainly prefer this to the horribly hacky one.

That said, I still think we could easily just split up 
"move_page_tables()" into two functions - one that just does the page 
table allocation, and one that actually moves the entries.

In fact, I think that would even clean up the error case for move_vma() 
too - the page table entry movement itself could never fail, so you never 
end up with that insane "move back" case.

		Linus