linux-kernel - RE: [PATCH RESEND] memory hotplug: fix a double register section info bug

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Date:	Fri, 14 Sep 2012 16:24:32 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Mel Gorman <mgorman@...e.de>, qiuxishi <qiuxishi@...il.com>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	"qiuxishi@...wei.com" <qiuxishi@...wei.com>,
	"bessel.wang@...wei.com" <bessel.wang@...wei.com>,
	"wujianguo@...wei.com" <wujianguo@...wei.com>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wen Congyang <wency@...fujitsu.com>
Subject: RE: [PATCH RESEND] memory hotplug: fix a double register section
 info bug

> This is an unusual configuration but it's not unheard of. PPC64 in rare
> (and usually broken) configurations can have one node span another. Tony
> should know if such a configuration is normally allowed on Itanium or if
> this should be considered a platform bug. Tony?

We definitely have platforms where the physical memory on node 0
that we skipped to leave physical address space for PCI mem mapped
devices gets tagged back at the very top of memory, after other nodes.

E.g. A 2-node system with 8G on each might look like this:

0-2G RAM on node 0
2G-4G  PCI map space
4G-8G RAM on node 0
8G-16GRAM on node 1
16G-18G RAM on node 0

Is this the situation that we are talking about? Or something different?

-Tony
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