linux-kernel - Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or not when removing memory

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Message-ID: <CAHGf_=q=Agidyj_j6jhBdhNmJBy2u1dP+UMAoXbM=_=DyZJs_w@mail.gmail.com>
Date:	Fri, 19 Oct 2012 14:33:17 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wen Congyang <wencongyang@...il.com>
Cc:	Wen Congyang <wency@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	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
Subject: Re: [PATCH 1/10] memory-hotplug : check whether memory is offline or
 not when removing memory

> 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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