linux-kernel - Re: [PATCH 09/10] memory-hotplug: enable memory hotplug to handle hugepage

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Date:	Tue, 9 Apr 2013 17:27:44 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/10] memory-hotplug: enable memory hotplug to handle hugepage

>> numa_node_id() is really silly. This might lead to allocate from offlining node.
>
> Right, it should've been alloc_huge_page().
>
>> and, offline_pages() should mark hstate as isolated likes normal pages for prohibiting
>> new allocation at first.
>
> It seems that alloc_migrate_target() calls alloc_page() for normal pages
> and the destination pages can be in the same node with the source pages
> (new page allocation from the same memblock are prohibited.)

No. It can't. memory hotplug change buddy attribute to MIGRATE_ISOLTE at first.
then alloc_page() never allocate from source node. however huge page don't use
buddy. then we need another trick.


> So if we want to avoid new page allocation from the same node,
> this is the problem both for normal and huge pages.
>
> BTW, is it correct to think that all users of memory hotplug assume
> that they want to hotplug a whole node (not the part of it?)

Both are valid use case. admin can isolate a part of memory for isolating
broken memory range.

but I'm sure almost user want to remove whole node.
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