linux-kernel - Re: [PATCH] memory-hotplug: fix zone stat mismatch

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Message-ID: <505A6EB7.5070305@cn.fujitsu.com>
Date:	Thu, 20 Sep 2012 09:17:43 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Shaohua Li <shli@...ionio.com>
Subject: Re: [PATCH] memory-hotplug: fix zone stat mismatch

At 09/20/2012 04:17 AM, Minchan Kim Wrote:
> Hi KOSAKI,
> 
> On Wed, Sep 19, 2012 at 02:05:20PM -0400, KOSAKI Motohiro wrote:
>> On Wed, Sep 19, 2012 at 3:29 AM, Minchan Kim <minchan@...nel.org> wrote:
>>> During memory-hotplug stress test, I found NR_ISOLATED_[ANON|FILE]
>>> are increasing so that kernel are hang out.
>>>
>>> The cause is that when we do memory-hotadd after memory-remove,
>>> __zone_pcp_update clear out zone's ZONE_STAT_ITEMS in setup_pageset
>>> without draining vm_stat_diff of all CPU.
>>>
>>> This patch fixes it.
>>
>> zone_pcp_update() is called from online pages path. but IMHO,
>> the statistics should be drained offline path. isn't it?
> 
> It isn't necessary because statistics is right until we reset it to zero
> in online path.
> Do you have something on your mind that we have to drain it in offline path?

When a node is offlined and onlined again. We create node_data[i] in the
function hotadd_new_pgdat(), and we will lost the statistics stored in
zone->pageset. So we should drain it in offline path.

Thanks
Wen Congyang

> 
>>
>> thanks.
> 

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