From: Cody P Schafer <cody@linux.vnet.ibm.com>
Date: Wed, 3 Jul 2013 22:01:31 +0000 (-0700)
Subject: mm/page_alloc: insert memory barriers to allow async update of pcp batch and high
X-Git-Tag: omap-for-v3.11/fixes-for-merge-window~17^2~402
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8d7a8fa97abeb4fd6b3975d32c9f859875157770;p=pandora-kernel.git

mm/page_alloc: insert memory barriers to allow async update of pcp batch and high

Introduce pageset_update() to perform a safe transision from one set of
pcp->{batch,high} to a new set using memory barriers.

This ensures that batch is always set to a safe value (1) prior to
updating high, and ensure that high is fully updated before setting the
real value of batch.  It avoids ->batch ever rising above ->high.

Suggested by Gilad Ben-Yossef in these threads:

	https://lkml.org/lkml/2013/4/9/23
	https://lkml.org/lkml/2013/4/10/49

Also reproduces his proposed comment.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Reviewed-by: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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