linux-kernel - Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, use on_each

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Message-ID: <516317A9.7040208@gmail.com>
Date:	Mon, 08 Apr 2013 15:16:57 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	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 3/3] mm: when handling percpu_pagelist_fraction, use on_each_cpu()
 to set percpu pageset fields.

(4/8/13 8:20 AM), Gilad Ben-Yossef wrote:
> On Fri, Apr 5, 2013 at 11:33 PM, Cody P Schafer <cody@...ux.vnet.ibm.com> wrote:
>> In free_hot_cold_page(), we rely on pcp->batch remaining stable.
>> Updating it without being on the cpu owning the percpu pageset
>> potentially destroys this stability.
>>
>> Change for_each_cpu() to on_each_cpu() to fix.
> 
> Are you referring to this? -
> 
> 1329         if (pcp->count >= pcp->high) {
> 1330                 free_pcppages_bulk(zone, pcp->batch, pcp);
> 1331                 pcp->count -= pcp->batch;
> 1332         }
> 
> I'm probably missing the obvious but won't it be simpler to do this in
>  free_hot_cold_page() -
> 
> 1329         if (pcp->count >= pcp->high) {
> 1330                  unsigned int batch = ACCESS_ONCE(pcp->batch);
> 1331                 free_pcppages_bulk(zone, batch, pcp);
> 1332                 pcp->count -= batch;
> 1333         }
> 
> Now the batch value used is stable and you don't have to IPI every CPU
> in the system just to change a config knob...

OK, right. Your approach is much better.


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