linux-kernel - Re: [RFC][PATCH] release mmap_sem before starting migration (Was Re: Need to take mmap_sem lock in move

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Message-ID: <alpine.DEB.1.10.0902041037150.19633@qirst.com>
Date:	Wed, 4 Feb 2009 10:39:19 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Swamy Gowda <swamy@...ident.com>, linux-kernel@...r.kernel.org,
	Brice.Goglin@...ia.fr, "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] release mmap_sem before starting migration (Was
 Re: Need to take mmap_sem lock in move_pages.

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.


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