linux-kernel - Re: [PATCH 01/18] mm, hugetlb: protect reserved pages when softofflining requests the pages

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Message-ID: <CAJd=RBD=SNm9TG-kxKcd-BiMduOhLUubq=JpRwCy_MmiDtO9Tw@mail.gmail.com>
Date:	Wed, 31 Jul 2013 10:49:24 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH 01/18] mm, hugetlb: protect reserved pages when
 softofflining requests the pages

On Wed, Jul 31, 2013 at 10:27 AM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> On Mon, Jul 29, 2013 at 03:24:46PM +0800, Hillf Danton wrote:
>> On Mon, Jul 29, 2013 at 1:31 PM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
>> > alloc_huge_page_node() use dequeue_huge_page_node() without
>> > any validation check, so it can steal reserved page unconditionally.
>>
>> Well, why is it illegal to use reserved page here?
>
> If we use reserved page here, other processes which are promised to use
> enough hugepages cannot get enough hugepages and can die. This is
> unexpected result to them.
>
But, how do you determine that a huge page is requested by a process
that is not allowed to use reserved pages?
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