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

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Date:	Mon, 20 Apr 2015 10:08:43 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
	Xishi Qiu <qiuxishi@...wei.com>
CC:	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()

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,
and 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

> 
> Thanks,
> Yasuaki Ishimatsu
> 
> On 
> Yasuaki Ishimatsu <yasu.isimatu@...il.com> 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.
>>
>> Thanks,
>> Yasuaki Ishimatsu
>>
>> On Mon, 20 Apr 2015 09:33:10 +0800
>> Xishi Qiu <qiuxishi@...wei.com> wrote:
>>
>>> On 2015/4/18 4:05, Yasuaki Ishimatsu wrote:
>>>
>>>>
>>>> Your patches will fix your issue.
>>>> But, if BIOS reports memory first at node hot add, pgdat can
>>>> not be initialized.
>>>>
>>>> Memory hot add flows are as follows:
>>>>
>>>> add_memory
>>>>   ...
>>>>   -> hotadd_new_pgdat()
>>>>   ...
>>>>   -> node_set_online(nid)
>>>>
>>>> When calling hotadd_new_pgdat() for a hot added node, the node is
>>>> offline because node_set_online() is not called yet. So if applying
>>>> your patches, the pgdat is not initialized in this case.
>>>>
>>>> Thanks,
>>>> Yasuaki Ishimatsu
>>>>
>>>
>>> Hi Yasuaki,
>>>
>>> I'm not quite understand, when BIOS reports memory first, why pgdat
>>> can not be initialized?
>>> When hotadd a new node, hotadd_new_pgdat() will be called too, and
>>> when hotadd memory to a existent node, it's no need to call hotadd_new_pgdat(),
>>> right?
>>>
>>> Thanks,
>>> Xishi Qiu
>>>
> .
> 


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