linux-kernel - Re: [RFC PATCH 2/12] memory-hogplug : check memory offline in offline

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Date:	Thu, 28 Jun 2012 15:01:38 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Wen Congyang <wency@...fujitsu.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-acpi@...r.kernel.org>, <len.brown@...el.com>,
	<benh@...nel.crashing.org>, <paulus@...ba.org>, <cl@...ux.com>,
	<minchan.kim@...il.com>, <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 2/12] memory-hogplug : check memory offline in offline_pages

Hi Kosaki-san,

2012/06/28 14:27, KOSAKI Motohiro wrote:
> On Thu, Jun 28, 2012 at 1:06 AM, Yasuaki Ishimatsu
> <isimatu.yasuaki@...fujitsu.com> wrote:
>> Hi Wen,
>>
>> 2012/06/27 17:49, Wen Congyang wrote:
>>> At 06/27/2012 01:44 PM, Yasuaki Ishimatsu Wrote:
>>>> When offline_pages() is called to offlined memory, the function fails since
>>>> all memory has been offlined. In this case, the function should succeed.
>>>> The patch adds the check function into offline_pages().
>>>
>>> You miss such case: some pages are online, while some pages are offline.
>>> offline_pages() will fail too in such case.
>>
>> You are right. But current code fails, when the function is called to offline
>> memory. In this case, the function should succeed. So the patch confirms
>> whether the memory was offlined or not. And if memory has already been
>> offlined, offline_pages return 0.
>
> Can you please explain why the caller can't check it? I hope to avoid
> an ignorance
> as far as we can.

Of course, caller side can check it. But there is a possibility that
offline_pages() is called by many functions. So I do not think that it
is good that all functions which call offline_pages() check it.

Thanks,
Yasuaki Ishimatsu

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