Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161978Ab3DEIyz (ORCPT ); Fri, 5 Apr 2013 04:54:55 -0400 Received: from mail-pd0-f174.google.com ([209.85.192.174]:44083 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751127Ab3DEIyw (ORCPT ); Fri, 5 Apr 2013 04:54:52 -0400 Message-ID: <515E9154.6050709@gmail.com> Date: Fri, 05 Apr 2013 16:54:44 +0800 From: Simon Jeons User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: Michal Hocko CC: Wanpeng Li , 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 References: <1365066554-29195-1-git-send-email-liwanp@linux.vnet.ibm.com> <20130404161746.GP29911@dhcp22.suse.cz> <20130404234123.GA362@hacker.(null)> <20130405081239.GC14882@dhcp22.suse.cz> In-Reply-To: <20130405081239.GC14882@dhcp22.suse.cz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1982 Lines: 38 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". > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/