linux-kernel - Re: [PATCH 1/2 V2] memory_hotplug: fix possible incorrect node_states[N_NORMAL

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Date:	Fri, 26 Oct 2012 09:20:40 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Rob Landley <rob@...dley.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Mel Gorman <mgorman@...e.de>,
	FNST-Wen Congyang <wency@...fujitsu.com>,
	linux-doc@...r.kernel.org, linux-mm@...ck.org,
	Jianguo Wu <wujianguo@...wei.com>,
	Xishi Qiu <qiuxishi@...wei.com>
Subject: Re: [PATCH 1/2 V2] memory_hotplug: fix possible incorrect node_states[N_NORMAL_MEMORY]

On 10/25/2012 12:17 PM, KOSAKI Motohiro wrote:
> On Wed, Oct 24, 2012 at 5:43 AM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
>> Currently memory_hotplug only manages the node_states[N_HIGH_MEMORY],
>> it forgets to manage node_states[N_NORMAL_MEMORY]. it may cause
>> node_states[N_NORMAL_MEMORY] becomes incorrect.
>>
>> Example, if a node is empty before online, and we online a memory
>> which is in ZONE_NORMAL. And after online,  node_states[N_HIGH_MEMORY]
>> is correct, but node_states[N_NORMAL_MEMORY] is incorrect,
>> the online code don't set the new online node to
>> node_states[N_NORMAL_MEMORY].
>>
>> The same things like it will happen when offline(the offline code
>> don't clear the node from node_states[N_NORMAL_MEMORY] when needed).
>> Some memory managment code depends node_states[N_NORMAL_MEMORY],
>> so we have to fix up the node_states[N_NORMAL_MEMORY].
>>
>> We add node_states_check_changes_online() and node_states_check_changes_offline()
>> to detect whether node_states[N_HIGH_MEMORY] and node_states[N_NORMAL_MEMORY]
>> are changed while hotpluging.
>>
>> Also add @status_change_nid_normal to struct memory_notify, thus
>> the memory hotplug callbacks know whether the node_states[N_NORMAL_MEMORY]
>> are changed. (We can add a @flags and reuse @status_change_nid instead of
>> introducing @status_change_nid_normal, but it will add much more complicated
>> in memory hotplug callback in every subsystem. So introdcing
>> @status_change_nid_normal is better and it don't change the sematic
>> of @status_change_nid)
>>
>> Changed from V1:
>>         add more comments
>>         change the function name
> 
> Your patch didn't fix my previous comments and don't works correctly.
> Please test your own patch before resubmitting. You should consider both
> zone normal only node and zone high only node.
> 

The comments in the code already answered/explained your previous comments.

Thanks,
Lai
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