linux-kernel - Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu() instead of stop

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Date:	Sun, 07 Apr 2013 11:39:06 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, kosaki.motohiro@...il.com
Subject: Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu()
 instead of stop_machine()

(4/5/13 4:33 PM), Cody P Schafer wrote:
> No off-cpu users of the percpu pagesets exist.
> 
> zone_pcp_update()'s goal is to adjust the ->high and ->mark members of a
> percpu pageset based on a zone's ->managed_pages. We don't need to drain
> the entire percpu pageset just to modify these fields. Avoid calling
> setup_pageset() (and the draining required to call it) and instead just
> set the fields' values.
> 
> This does change the behavior of zone_pcp_update() as the percpu
> pagesets will not be drained when zone_pcp_update() is called (they will
> end up being shrunk, not completely drained, later when a 0-order page
> is freed in free_hot_cold_page()).
> 
> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>

NAK.

1) zone_pcp_update() is only used from memory hotplug and it require page drain.
2) stop_machin is used for avoiding race. just removing it is insane.


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