From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751744AbeAaUcp (ORCPT ); Wed, 31 Jan 2018 15:32:45 -0500 Received: from mx2.suse.de ([195.135.220.15]:39011 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751580AbeAaUco (ORCPT ); Wed, 31 Jan 2018 15:32:44 -0500 Date: Wed, 31 Jan 2018 21:32:42 +0100 From: Michal Hocko To: Andrew Morton Cc: Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] mm/migrate: Add new migration reason MR_HUGETLB Message-ID: <20180131203242.GB21609@dhcp22.suse.cz> References: <20180130030714.6790-1-khandual@linux.vnet.ibm.com> <20180130075949.GN21609@dhcp22.suse.cz> <20180131075852.GL21609@dhcp22.suse.cz> <20180131121217.4c80263d68a4ad4da7b170f0@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180131121217.4c80263d68a4ad4da7b170f0@linux-foundation.org> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 31-01-18 12:12:17, Andrew Morton wrote: > On Wed, 31 Jan 2018 08:58:52 +0100 Michal Hocko wrote: > > > On Wed 31-01-18 07:55:05, Anshuman Khandual wrote: > > > On 01/30/2018 01:29 PM, Michal Hocko wrote: > > > > On Tue 30-01-18 08:37:14, Anshuman Khandual wrote: > > > >> alloc_contig_range() initiates compaction and eventual migration for > > > >> the purpose of either CMA or HugeTLB allocation. At present, reason > > > >> code remains the same MR_CMA for either of those cases. Lets add a > > > >> new reason code which will differentiate the purpose of migration > > > >> as HugeTLB allocation instead. > > > > Why do we need it? > > > > > > The same reason why we have MR_CMA (maybe some other ones as well) at > > > present, for reporting purpose through traces at the least. It just > > > seemed like same reason code is being used for two different purpose > > > of migration. > > > > But do we have any real user asking for this kind of information? > > It seems a reasonable cleanup: reusing MR_CMA for hugetlb just because > it happens to do the right thing is a bit hacky - the two things aren't > particularly related and a reader could be excused for feeling > confusion. My bad! I thought this is a tracepoint thingy. But it seems to be only used as a migration reason for page_owner. Now it makes more sense. > But the change seems incomplete: > > > + if (migratetype == MIGRATE_CMA) > > + migrate_reason = MR_CMA; > > + else > > + migrate_reason = MR_HUGETLB; > > If we're going to do this cleanup then shouldn't we go all the way and > add MIGRATE_HUGETLB? Yes. We can expect more users of alloc_contig_range in future. Maybe we want to use MR_CONTIG_RANGE instead. -- Michal Hocko SUSE Labs