From: Michal Hocko <mhocko@suse.cz>
To: Simon Jeons <simon.jeons@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
Hillf Danton <dhillf@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting
Date: Fri, 5 Apr 2013 11:52:58 +0200 [thread overview]
Message-ID: <20130405095258.GC31132@dhcp22.suse.cz> (raw)
In-Reply-To: <515E9154.6050709@gmail.com>
On Fri 05-04-13 16:54:44, Simon Jeons wrote:
> Hi Michal,
> On 04/05/2013 04:12 PM, Michal Hocko wrote:
> >On Fri 05-04-13 07:41:23, Wanpeng Li wrote:
> >>On Thu, Apr 04, 2013 at 06:17:46PM +0200, Michal Hocko wrote:
> >>>On Thu 04-04-13 17:09:08, Wanpeng Li wrote:
> >>>>order >= MAX_ORDER pages are only allocated at boot stage using the
> >>>>bootmem allocator with the "hugepages=xxx" option. These pages are never
> >>>>free after boot by default since it would be a one-way street(>= MAX_ORDER
> >>>>pages cannot be allocated later), but if administrator confirm not to
> >>>>use these gigantic pages any more, these pinned pages will waste memory
> >>>>since other users can't grab free pages from gigantic hugetlb pool even
> >>>>if OOM, it's not flexible. The patchset add hugetlb gigantic page pools
> >>>>shrink supporting. Administrator can enable knob exported in sysctl to
> >>>>permit to shrink gigantic hugetlb pool.
> >>>I am not sure I see why the new knob is needed.
> >>>/sys/kernel/mm/hugepages/hugepages-*/nr_hugepages is root interface so
> >>>an additional step to allow writing to the file doesn't make much sense
> >>>to me to be honest.
> >>>
> >>>Support for shrinking gigantic huge pages makes some sense to me but I
> >>>would be interested in the real world example. GB pages are usually used
> >>>in very specific environments where the amount is usually well known.
> >>Gigantic huge pages in hugetlb means h->order >= MAX_ORDER instead of GB
> >>pages. ;-)
> >Yes, I am aware of that but the question remains the same (and
> >unanswered). What is the use case?
>
> As patch description, "if administrator confirm not to use these
> gigantic pages any more, these pinned pages will waste memory since
> other users can't grab free pages from gigantic hugetlb pool even if
> OOM".
Is this a use case that we care about? How often something like that
happens? I understand this is "nice to have" but I am interested whether
somebody actually _needs_ this.
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2013-04-05 9:53 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-04 9:09 Wanpeng Li
2013-04-04 9:09 ` [PATCH 1/6] mm/hugetlb: introduce new sysctl knob which control gigantic page pools shrinking Wanpeng Li
2013-04-04 9:09 ` [PATCH 2/6] mm/hugetlb: update_and_free_page gigantic pages awareness Wanpeng Li
2013-04-04 9:09 ` [PATCH 3/6] mm/hugetlb: enable gigantic hugetlb page pools shrinking Wanpeng Li
2013-04-04 9:09 ` [PATCH 4/6] mm/hugetlb: use already exist huge_page_order() instead of h->order Wanpeng Li
2013-04-04 9:09 ` [PATCH 5/6] mm/hugetlb: remove redundant hugetlb_prefault Wanpeng Li
2013-04-04 9:09 ` [PATCH 6/6] mm/hugetlb: use already exist interface huge_page_shift Wanpeng Li
2013-04-04 16:17 ` [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting Michal Hocko
2013-04-04 16:20 ` Michal Hocko
2013-04-05 1:29 ` Wanpeng Li
2013-04-05 1:29 ` Wanpeng Li
2013-04-04 23:41 ` Wanpeng Li
2013-04-05 8:12 ` Michal Hocko
2013-04-05 8:27 ` Wanpeng Li
2013-04-05 8:27 ` Wanpeng Li
2013-04-05 9:27 ` Michal Hocko
2013-04-05 8:54 ` Simon Jeons
2013-04-05 9:52 ` Michal Hocko [this message]
2013-04-04 23:41 ` Wanpeng Li
2013-04-04 23:35 ` Wanpeng Li
2013-04-04 23:35 ` Wanpeng Li
2013-04-11 23:29 ` Wanpeng Li
2013-04-11 23:29 ` Wanpeng Li
2013-04-12 15:22 ` Andi Kleen
2013-07-15 11:31 ` Wanpeng Li
2013-07-15 11:31 ` Wanpeng Li
2014-08-21 23:37 ` Wanpeng Li
2014-08-22 1:34 ` Zhang Yanfei
2014-08-22 4:04 ` Wanpeng Li
2014-08-22 14:18 ` Andi Kleen
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