linux-kernel - Re: [PATCH 1/2 V2] memory-hotplug: fix BUG_ON in move

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Date:	Mon, 20 Apr 2015 10:59:37 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
CC:	Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	<izumi.taku@...fujitsu.com>, Tang Chen <tangchen@...fujitsu.com>,
	Xiexiuqi <xiexiuqi@...wei.com>, Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 V2] memory-hotplug: fix BUG_ON in move_freepages()

On 2015/4/20 10:09, Gu Zheng wrote:

> Hi Ishimatsu, Xishi,
> 
> On 04/20/2015 10:11 AM, Yasuaki Ishimatsu wrote:
> 
>>
>>> When hot adding memory and creating new node, the node is offline.
>>> And after calling node_set_online(), the node becomes online.
>>>
>>> Oh, sorry. I misread your ptaches.
>>>
>>
>> Please ignore it...
> 
> Seems also a misread to me.
> I clear it (my worry) here:
> If we set the node size to 0 here, it may hidden more things than we experted.
> All the init chunks around with the size (spanned/present/managed...) will
> be non-sense, and the user/caller will not get a summary of the hot added node
> because of the changes here.
> I am not sure the worry is necessary, please correct me if I missing something.
> 
> Regards,
> Gu
> 

Hi Gu,

My patch is just set size to 0 when hotadd a node(old or new). I know your worry,
but I think it is not necessary.

When we calculate the size, it uses "arch_zone_lowest_possible_pfn[]" and "memblock",
and they are both from boot time. If we hotadd a new node, the calculated size is
0 too. When add momery, __add_zone() will grow the size and start.

Thanks,
Xishi Qiu

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