linux-kernel - Re: [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

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Date:	Thu, 4 Apr 2013 18:20:23 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Hillf Danton <dhillf@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink
 supporting

On Thu 04-04-13 18:17:46, 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.
> 
> I could imagine nr_hugepages_mempolicy would make more sense to free
> pages from particular nodes so they could be offlined for example.
> Does the patchset handles this as well?
 
Ohh, I should have checked before asking. Both knobs use the same
hugetlb_sysctl_handler_common and unless there is something hardcoded in
the patches then it should be supproted.

-- 
Michal Hocko
SUSE Labs
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