Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754660AbdHYHir (ORCPT ); Fri, 25 Aug 2017 03:38:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:47690 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754456AbdHYHiq (ORCPT ); Fri, 25 Aug 2017 03:38:46 -0400 Date: Fri, 25 Aug 2017 09:38:42 +0200 From: Michal Hocko To: Joonsoo Kim Cc: Vlastimil Babka , Andrew Morton , Mel Gorman , Johannes Weiner , "Aneesh Kumar K . V" , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request Message-ID: <20170825073841.GD25498@dhcp22.suse.cz> References: <1503553546-27450-1-git-send-email-iamjoonsoo.kim@lge.com> <20170825002031.GD29701@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170825002031.GD29701@js1304-P5Q-DELUXE> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2014 Lines: 52 On Fri 25-08-17 09:20:31, Joonsoo Kim wrote: > On Thu, Aug 24, 2017 at 11:41:58AM +0200, Vlastimil Babka wrote: > > On 08/24/2017 07:45 AM, js1304@gmail.com wrote: > > > From: Joonsoo Kim > > > > > > Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that > > > important to reserve. When ZONE_MOVABLE is used, this problem would > > > theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE > > > allocation request which is mainly used for page cache and anon page > > > allocation. So, fix it. > > > > > > And, defining sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES - 1 size > > > makes code complex. For example, if there is highmem system, following > > > reserve ratio is activated for *NORMAL ZONE* which would be easyily > > > misleading people. > > > > > > #ifdef CONFIG_HIGHMEM > > > 32 > > > #endif > > > > > > This patch also fix this situation by defining sysctl_lowmem_reserve_ratio > > > array by MAX_NR_ZONES and place "#ifdef" to right place. > > > > > > Reviewed-by: Aneesh Kumar K.V > > > Acked-by: Vlastimil Babka > > > > Looks like I did that almost year ago, so definitely had to refresh my > > memory now :) > > > > Anyway now I looked more thoroughly and noticed that this change leaks > > into the reported sysctl. On a 64bit system with ZONE_MOVABLE: > > > > before the patch: > > vm.lowmem_reserve_ratio = 256 256 32 > > > > after the patch: > > vm.lowmem_reserve_ratio = 256 256 32 2147483647 > > > > So if we indeed remove HIGHMEM from protection (c.f. Michal's mail), we > > should do that differently than with the INT_MAX trick, IMHO. > > Hmm, this is already pointed by Minchan and I have answered that. > > lkml.kernel.org/r/<20170421013243.GA13966@js1304-desktop> > > If you have a better idea, please let me know. Why don't we just use 0. In fact we are reserving 0 pages... Using INT_MAX is just wrong. -- Michal Hocko SUSE Labs