linux-kernel - 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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Date:	Fri, 7 May 2010 07:18:39 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.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

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
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