Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752328AbdHXJmD (ORCPT ); Thu, 24 Aug 2017 05:42:03 -0400 Received: from mx2.suse.de ([195.135.220.15]:55002 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752020AbdHXJmB (ORCPT ); Thu, 24 Aug 2017 05:42:01 -0400 Subject: Re: [PATCH] mm/page_alloc: don't reserve ZONE_HIGHMEM for ZONE_MOVABLE request To: js1304@gmail.com, Andrew Morton Cc: Michal Hocko , Mel Gorman , Johannes Weiner , "Aneesh Kumar K . V" , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim References: <1503553546-27450-1-git-send-email-iamjoonsoo.kim@lge.com> From: Vlastimil Babka Message-ID: Date: Thu, 24 Aug 2017 11:41:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <1503553546-27450-1-git-send-email-iamjoonsoo.kim@lge.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3120 Lines: 87 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. > Signed-off-by: Joonsoo Kim > --- > include/linux/mmzone.h | 2 +- > mm/page_alloc.c | 11 ++++++----- > 2 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index e7e92c8..e5f134b 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -882,7 +882,7 @@ int min_free_kbytes_sysctl_handler(struct ctl_table *, int, > void __user *, size_t *, loff_t *); > int watermark_scale_factor_sysctl_handler(struct ctl_table *, int, > void __user *, size_t *, loff_t *); > -extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1]; > +extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES]; > int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int, > void __user *, size_t *, loff_t *); > int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int, > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 90b1996..6faa53d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -202,17 +202,18 @@ static void __free_pages_ok(struct page *page, unsigned int order); > * TBD: should special case ZONE_DMA32 machines here - in those we normally > * don't need any ZONE_NORMAL reservation > */ > -int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = { > +int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES] = { > #ifdef CONFIG_ZONE_DMA > - 256, > + [ZONE_DMA] = 256, > #endif > #ifdef CONFIG_ZONE_DMA32 > - 256, > + [ZONE_DMA32] = 256, > #endif > + [ZONE_NORMAL] = 32, > #ifdef CONFIG_HIGHMEM > - 32, > + [ZONE_HIGHMEM] = INT_MAX, > #endif > - 32, > + [ZONE_MOVABLE] = INT_MAX, > }; > > EXPORT_SYMBOL(totalram_pages); >