From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161588Ab3DEIMq (ORCPT ); Fri, 5 Apr 2013 04:12:46 -0400 Received: from cantor2.suse.de ([195.135.220.15]:45599 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751817Ab3DEIMm (ORCPT ); Fri, 5 Apr 2013 04:12:42 -0400 Date: Fri, 5 Apr 2013 10:12:39 +0200 From: Michal Hocko To: Wanpeng Li Cc: Andrew Morton , KAMEZAWA Hiroyuki , "Aneesh Kumar K.V" , Mel Gorman , Rik van Riel , Hillf Danton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting Message-ID: <20130405081239.GC14882@dhcp22.suse.cz> References: <1365066554-29195-1-git-send-email-liwanp@linux.vnet.ibm.com> <20130404161746.GP29911@dhcp22.suse.cz> <20130404234123.GA362@hacker.(null)> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130404234123.GA362@hacker.(null)> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Michal Hocko SUSE Labs