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

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Date:	Fri, 12 Apr 2013 17:22:37 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Michal Hocko <mhocko@...e.cz>, 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 Fri, Apr 12, 2013 at 07:29:07AM +0800, Wanpeng Li wrote:
> Ping Andi,
> On Thu, Apr 04, 2013 at 05:09:08PM +0800, 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 originally didn't allow this because it's only one way and it seemed
dubious.  I've been recently working on a new patchkit to allocate
GB pages from CMA. With that freeing actually makes sense, as 
the pages can be reallocated.

-Andi
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