From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753474AbdGSJdy (ORCPT ); Wed, 19 Jul 2017 05:33:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:60818 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752842AbdGSJdv (ORCPT ); Wed, 19 Jul 2017 05:33:51 -0400 Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE To: Michal Hocko , linux-mm@kvack.org Cc: Andrew Morton , Mel Gorman , Johannes Weiner , LKML , Michal Hocko , linux-api@vger.kernel.org References: <20170714080006.7250-1-mhocko@kernel.org> <20170714080006.7250-2-mhocko@kernel.org> From: Vlastimil Babka Message-ID: Date: Wed, 19 Jul 2017 11:33:49 +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: <20170714080006.7250-2-mhocko@kernel.org> 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 On 07/14/2017 09:59 AM, Michal Hocko wrote: > From: Michal Hocko > > Supporting zone ordered zonelists costs us just a lot of code while > the usefulness is arguable if existent at all. Mel has already made > node ordering default on 64b systems. 32b systems are still using > ZONELIST_ORDER_ZONE because it is considered better to fallback to > a different NUMA node rather than consume precious lowmem zones. > > This argument is, however, weaken by the fact that the memory reclaim > has been reworked to be node rather than zone oriented. This means > that lowmem requests have to skip over all highmem pages on LRUs already > and so zone ordering doesn't save the reclaim time much. So the only > advantage of the zone ordering is under a light memory pressure when > highmem requests do not ever hit into lowmem zones and the lowmem > pressure doesn't need to reclaim. > > Considering that 32b NUMA systems are rather suboptimal already and > it is generally advisable to use 64b kernel on such a HW I believe we > should rather care about the code maintainability and just get rid of > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if > somebody tries to set zone ordering either from kernel command line > or the sysctl. > > Cc: > Signed-off-by: Michal Hocko Found some leftovers to cleanup: include/linux/mmzone.h: extern char numa_zonelist_order[]; #define NUMA_ZONELIST_ORDER_LEN 16 /* string buffer size */ Also update docs? Documentation/sysctl/vm.txt:zone. Specify "[Zz]one" for zone order. Documentation/admin-guide/kernel-parameters.txt: numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. Documentation/vm/numa:a default zonelist order based on the sizes of the various zone types relative Documentation/vm/numa:default zonelist order may be overridden using the numa_zonelist_order kernel Otherwise, Acked-by: Vlastimil Babka From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlastimil Babka Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Date: Wed, 19 Jul 2017 11:33:49 +0200 Message-ID: References: <20170714080006.7250-1-mhocko@kernel.org> <20170714080006.7250-2-mhocko@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170714080006.7250-2-mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Content-Language: en-US Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org Cc: Andrew Morton , Mel Gorman , Johannes Weiner , LKML , Michal Hocko , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On 07/14/2017 09:59 AM, Michal Hocko wrote: > From: Michal Hocko > > Supporting zone ordered zonelists costs us just a lot of code while > the usefulness is arguable if existent at all. Mel has already made > node ordering default on 64b systems. 32b systems are still using > ZONELIST_ORDER_ZONE because it is considered better to fallback to > a different NUMA node rather than consume precious lowmem zones. > > This argument is, however, weaken by the fact that the memory reclaim > has been reworked to be node rather than zone oriented. This means > that lowmem requests have to skip over all highmem pages on LRUs already > and so zone ordering doesn't save the reclaim time much. So the only > advantage of the zone ordering is under a light memory pressure when > highmem requests do not ever hit into lowmem zones and the lowmem > pressure doesn't need to reclaim. > > Considering that 32b NUMA systems are rather suboptimal already and > it is generally advisable to use 64b kernel on such a HW I believe we > should rather care about the code maintainability and just get rid of > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if > somebody tries to set zone ordering either from kernel command line > or the sysctl. > > Cc: > Signed-off-by: Michal Hocko Found some leftovers to cleanup: include/linux/mmzone.h: extern char numa_zonelist_order[]; #define NUMA_ZONELIST_ORDER_LEN 16 /* string buffer size */ Also update docs? Documentation/sysctl/vm.txt:zone. Specify "[Zz]one" for zone order. Documentation/admin-guide/kernel-parameters.txt: numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. Documentation/vm/numa:a default zonelist order based on the sizes of the various zone types relative Documentation/vm/numa:default zonelist order may be overridden using the numa_zonelist_order kernel Otherwise, Acked-by: Vlastimil Babka From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 6E7B86B0279 for ; Wed, 19 Jul 2017 05:33:52 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id g15so2324164wmi.11 for ; Wed, 19 Jul 2017 02:33:52 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b31si3756718wrd.66.2017.07.19.02.33.50 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 19 Jul 2017 02:33:51 -0700 (PDT) Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE References: <20170714080006.7250-1-mhocko@kernel.org> <20170714080006.7250-2-mhocko@kernel.org> From: Vlastimil Babka Message-ID: Date: Wed, 19 Jul 2017 11:33:49 +0200 MIME-Version: 1.0 In-Reply-To: <20170714080006.7250-2-mhocko@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , linux-mm@kvack.org Cc: Andrew Morton , Mel Gorman , Johannes Weiner , LKML , Michal Hocko , linux-api@vger.kernel.org On 07/14/2017 09:59 AM, Michal Hocko wrote: > From: Michal Hocko > > Supporting zone ordered zonelists costs us just a lot of code while > the usefulness is arguable if existent at all. Mel has already made > node ordering default on 64b systems. 32b systems are still using > ZONELIST_ORDER_ZONE because it is considered better to fallback to > a different NUMA node rather than consume precious lowmem zones. > > This argument is, however, weaken by the fact that the memory reclaim > has been reworked to be node rather than zone oriented. This means > that lowmem requests have to skip over all highmem pages on LRUs already > and so zone ordering doesn't save the reclaim time much. So the only > advantage of the zone ordering is under a light memory pressure when > highmem requests do not ever hit into lowmem zones and the lowmem > pressure doesn't need to reclaim. > > Considering that 32b NUMA systems are rather suboptimal already and > it is generally advisable to use 64b kernel on such a HW I believe we > should rather care about the code maintainability and just get rid of > ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if > somebody tries to set zone ordering either from kernel command line > or the sysctl. > > Cc: > Signed-off-by: Michal Hocko Found some leftovers to cleanup: include/linux/mmzone.h: extern char numa_zonelist_order[]; #define NUMA_ZONELIST_ORDER_LEN 16 /* string buffer size */ Also update docs? Documentation/sysctl/vm.txt:zone. Specify "[Zz]one" for zone order. Documentation/admin-guide/kernel-parameters.txt: numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. Documentation/vm/numa:a default zonelist order based on the sizes of the various zone types relative Documentation/vm/numa:default zonelist order may be overridden using the numa_zonelist_order kernel Otherwise, Acked-by: Vlastimil Babka -- 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