Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or not when removing memory
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- To: Wen Congyang <wencongyang@xxxxxxxxx>
- Subject: Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or not when removing memory
- From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
- Date: Fri, 19 Oct 2012 14:33:17 -0400
- Cc: Wen Congyang <wency@xxxxxxxxxxxxxx>, Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>, x86@xxxxxxxxxx, linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, linux-acpi@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, cmetcalf@xxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, rientjes@xxxxxxxxxx, liuj97@xxxxxxxxx, len.brown@xxxxxxxxx, cl@xxxxxxxxx, minchan.kim@xxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx
- In-reply-to: <5081609C.9080702@gmail.com>
- List-id: <linux-ia64.vger.kernel.org>
- References: <506E43E0.70507@jp.fujitsu.com> <506E451E.1050403@jp.fujitsu.com> <CAHGf_=rVDm-JygjPoLHbmF28Dgd52HFc4-b5KCxhEieG60okuw@mail.gmail.com> <50812F13.20503@cn.fujitsu.com> <5081609C.9080702@gmail.com>
> I think it again, and found that this check is necessary. Because we only
> lock memory hotplug when offlining pages. Here is the steps to offline and
> remove memory:
>
> 1. lock memory hotplug
> 2. offline a memory section
> 3. unlock memory hotplug
> 4. repeat 1-3 to offline all memory sections
> 5. lock memory hotplug
> 6. remove memory
> 7. unlock memory hotplug
>
> All memory sections must be offlined before removing memory. But we don't
> hold
> the lock in the whole operation. So we should check whether all memory
> sections
> are offlined before step6.
You should describe the race scenario in the patch description. OK?
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