From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 116146B025F for ; Sun, 27 Aug 2017 20:15:17 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id a2so11501888pfj.2 for ; Sun, 27 Aug 2017 17:15:17 -0700 (PDT) Received: from lgeamrelo12.lge.com (LGEAMRELO12.lge.com. [156.147.23.52]) by mx.google.com with ESMTP id w61si2203736plb.817.2017.08.27.17.15.15 for ; Sun, 27 Aug 2017 17:15:15 -0700 (PDT) Date: Mon, 28 Aug 2017 09:15:52 +0900 From: Joonsoo Kim Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request Message-ID: <20170828001551.GA9167@js1304-P5Q-DELUXE> References: <1503553546-27450-1-git-send-email-iamjoonsoo.kim@lge.com> <20170825002031.GD29701@js1304-P5Q-DELUXE> <20170825073841.GD25498@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170825073841.GD25498@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Vlastimil Babka , Andrew Morton , Mel Gorman , Johannes Weiner , "Aneesh Kumar K . V" , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, Aug 25, 2017 at 09:38:42AM +0200, Michal Hocko wrote: > 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. The number of reserved pages is calculated by "managed_pages / ratio". Using INT_MAX, net result would be 0. There is a logic converting ratio 0 to ratio 1. if (sysctl_lowmem_reserve_ratio[idx] < 1) sysctl_lowmem_reserve_ratio[idx] = 1 If I use 0 to represent 0 reserved page, there would be a user who is affected by this change. So, I don't use 0 for this patch. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org