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Date: Fri, 19 Nov 2010 20:26:01 +0100
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 02 of 66] 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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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mel@csn.ul.ie>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Avi Kivity <avi@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Rik van Riel <riel@redhat.com>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Ingo Molnar <mingo@elte.hu>, Mike Travis <travis@sgi.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Johannes Weiner <hannes@cmpxchg.org>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>, Chris Mason <chris.mason@oracle.com>, Borislav Petkov <bp@alien8.de>
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On Fri, Nov 19, 2010 at 09:54:27AM -0800, Linus Torvalds wrote:
> On Fri, Nov 19, 2010 at 9:38 AM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> >
> > We decided the kmalloc was ok, but Linus didn't like this approach. I
> > kept it in my tree because I didn't want to remember when/if to add the
> > special check in the accurate rmap walks. I find it simpler if all
> > rmap walks are accurate by default.
> 
> Why isn't the existing cheap solution sufficient?

It is sufficient.

> My opinion is still that we shouldn't add the expense to the common
> case, and it's the uncommon case (migration) that should just handle
> it.

Ok, I'll remove this patch from the next submit.

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