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

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Message-ID: <55346307.c32fec0a.3a9a.ffffce16@mx.google.com>
Date:	Sun, 19 Apr 2015 19:23:03 -0700 (PDT)
From:	Yasuaki Ishimatsu <yasu.isimatu@...il.com>
To:	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>,
	Gu Zheng <guz.fnst@...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 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?

Your patch sikps initialization of pgdat, when node is offline.
But when hot adding new node and calling hotadd_new_pgdat(), the node
is offline yet. So pgdat is not initialized. 

Thanks,
Yasuaki Ishimatsu

> 
> Thanks,
> Xishi Qiu
> 
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