linux-kernel - Re: [PATCH 0/10] memory-hotplug: hot-remove physical memory

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Date:	Fri, 5 Oct 2012 15:06:35 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
	len.brown@...el.com, cl@...ux.com, minchan.kim@...il.com,
	akpm@...ux-foundation.org, wency@...fujitsu.com
Subject: Re: [PATCH 0/10] memory-hotplug: hot-remove physical memory

> Known problems:
> 1. memory can't be offlined when CONFIG_MEMCG is selected.
>    For example: there is a memory device on node 1. The address range
>    is [1G, 1.5G). You will find 4 new directories memory8, memory9, memory10,
>    and memory11 under the directory /sys/devices/system/memory/.
>    If CONFIG_MEMCG is selected, we will allocate memory to store page cgroup
>    when we online pages. When we online memory8, the memory stored page cgroup
>    is not provided by this memory device. But when we online memory9, the memory
>    stored page cgroup may be provided by memory8. So we can't offline memory8
>    now. We should offline the memory in the reversed order.
>    When the memory device is hotremoved, we will auto offline memory provided
>    by this memory device. But we don't know which memory is onlined first, so
>    offlining memory may fail. In such case, you should offline the memory by
>    hand before hotremoving the memory device.

Just iterate twice. 1st iterate: offline every non primary memory
block. 2nd iterate:
offline primary (i.e. first added) memory block. It may work.
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