linux-kernel - Re: [PATCH] Revert "mm/page_alloc: protect pcp->batch accesses with ACCESS

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Date:	Wed, 30 Mar 2016 18:51:12 +0800
From:	Hekuang <hekuang@...wei.com>
To:	Mel Gorman <mgorman@...hsingularity.net>
CC:	<akpm@...ux-foundation.org>, <mhocko@...e.com>, <vbabka@...e.cz>,
	<rientjes@...gle.com>, <cody@...ux.vnet.ibm.com>,
	<gilad@...yossef.com>, <kosaki.motohiro@...il.com>,
	<mgorman@...e.de>, <penberg@...nel.org>, <lizefan@...wei.com>,
	<wangnan0@...wei.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "mm/page_alloc: protect pcp->batch accesses with
 ACCESS_ONCE"

hi

在 2016/3/30 18:38, Mel Gorman 写道:
> On Wed, Mar 30, 2016 at 10:22:07AM +0000, He Kuang wrote:
>> This reverts commit 998d39cb236fe464af86a3492a24d2f67ee1efc2.
>>
>> When local irq is disabled, a percpu variable does not change, so we can
>> remove the access macros and let the compiler optimize the code safely.
>>
> batch can be changed from other contexts. Why is this safe?
>
I've mistakenly thought that per_cpu variable can only be accessed by 
that cpu.
Thanks.