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Date: Wed, 4 Feb 2009 10:39:19 -0500 (EST)
From: Christoph Lameter <cl@linux-foundation.org>
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To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
cc: Swamy Gowda <swamy@virident.com>, linux-kernel@vger.kernel.org,
       Brice.Goglin@inria.fr, "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [RFC][PATCH] release mmap_sem before starting migration (Was
 Re: Need to take mmap_sem lock in move_pages.
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On Wed, 4 Feb 2009, KAMEZAWA Hiroyuki wrote:

> mmap_sem can be released after page table walk ends.

No. read lock on mmap_sem must be held since the migrate functions
manipulate page table entries. Concurrent large scale changes to the page
tables (splitting vmas, remapping etc) must not be possible.