linux-kernel - Re: [PATCH 8/9] memory-hotplug: enable memory hotplug to handle hugepage

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Date:	Thu, 21 Mar 2013 07:55:28 +0800
From:	Simon Jeons <simon.jeons@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] memory-hotplug: enable memory hotplug to handle hugepage

Hi Naoya,
On 03/21/2013 06:05 AM, Naoya Horiguchi wrote:
> On Wed, Mar 20, 2013 at 09:03:20AM +0800, Simon Jeons wrote:
>> Hi Naoya,
>> On 02/22/2013 03:41 AM, Naoya Horiguchi wrote:
>>> Currently we can't offline memory blocks which contain hugepages because
>>> a hugepage is considered as an unmovable page. But now with this patch
>>> series, a hugepage has become movable, so by using hugepage migration we
>>> can offline such memory blocks.
>>>
>>> What's different from other users of hugepage migration is that we need
>>> to decompose all the hugepages inside the target memory block into free
>> For other hugepage migration users, hugepage should be freed to
>> hugepage_freelists after migration, but why I don't see any codes do
>> this?
> The source hugepages which are migrated by NUMA related system calls
> (migrate_pages(2), move_pages(2), and mbind(2)) are still useable,
> so we simply free them into free hugepage pool.

It seems that you misunderstand why I confuse. I can't find where free
huge pages to hugepage pool, could you point out to me?

> OTOH, the source hugepages migrated by memory hotremove should not be
> reusable, because users of memory hotremove want to remove the memory
> from the system. So we need to free such hugepages forcibly into the
> buddy pages, otherwise memory offining doesn't work.
>
> Thanks,
> Naoya

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