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

From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>, Hugh Dickins <hughd@google.com>,
	Andi Kleen <andi@firstfloor.org>, Hillf Danton <dhillf@gmail.com>,
	Michal Hocko <mhocko@suse.cz>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 09/10] memory-hotplug: enable memory hotplug to handle hugepage
Date: Tue, 9 Apr 2013 21:56:58 -0400	[thread overview]
Message-ID: <CAHGf_=oL7dORGCJZtLxrwc9cGgrakAsfAOJ4xx659nDmQd=rcw@mail.gmail.com> (raw)
In-Reply-To: <1365547416-z92y6qa9-mutt-n-horiguchi@ah.jp.nec.com>

On Tue, Apr 9, 2013 at 6:43 PM, Naoya Horiguchi
<n-horiguchi@ah.jp.nec.com> wrote:
> On Tue, Apr 09, 2013 at 05:27:44PM -0400, KOSAKI Motohiro wrote:
>> >> 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.
>
> MIGRATE_ISOLTE is changed only within the range [start_pfn, end_pfn)
> given as the argument of __offline_pages (see also start_isolate_page_range),
> so it's set only for pages within the single memblock to be offlined.

When partial memory hot remove, that's correct behavior. different
node is not required.

> BTW, in previous discussion I already agreed with checking migrate type
> in hugepage allocation code (maybe it will be in dequeue_huge_page_vma(),)
> so what you concern should be solved in the next post.

Umm.. Maybe I missed such discussion. Do you have a pointer?

>> > 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.
>
> OK. So I think about "allocation in the nearest neighbor node",
> although it can be in separate patch if it's hard to implement.

That's fine.