From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B48EC433DB for ; Wed, 10 Feb 2021 09:45:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4C1964DDF for ; Wed, 10 Feb 2021 09:45:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230035AbhBJJpM (ORCPT ); Wed, 10 Feb 2021 04:45:12 -0500 Received: from mx2.suse.de ([195.135.220.15]:53724 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230125AbhBJJnS (ORCPT ); Wed, 10 Feb 2021 04:43:18 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id A5634AE91; Wed, 10 Feb 2021 09:42:31 +0000 (UTC) Date: Wed, 10 Feb 2021 10:42:28 +0100 From: Oscar Salvador To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, ben.widawsky@intel.com, rientjes@google.com, cl@linux.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, akpm@linux-foundation.org, ying.huang@intel.com, dan.j.williams@intel.com, cai@lca.pw, stable@vger.kernel.org Subject: Re: [RFC][PATCH 01/13] mm/vmscan: restore zone_reclaim_mode ABI Message-ID: <20210210094222.GA27173@linux> References: <20210126003411.2AC51464@viggo.jf.intel.com> <20210126003412.59594AA9@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210126003412.59594AA9@viggo.jf.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 25, 2021 at 04:34:13PM -0800, Dave Hansen wrote: > > From: Dave Hansen > > I went to go add a new RECLAIM_* mode for the zone_reclaim_mode > sysctl. Like a good kernel developer, I also went to go update the > documentation. I noticed that the bits in the documentation didn't > match the bits in the #defines. > > The VM never explicitly checks the RECLAIM_ZONE bit. The bit is, > however implicitly checked when checking 'node_reclaim_mode==0'. > The RECLAIM_ZONE #define was removed in a cleanup. That, by itself > is fine. > > But, when the bit was removed (bit 0) the _other_ bit locations also > got changed. That's not OK because the bit values are documented to > mean one specific thing and users surely rely on them meaning that one > thing and not changing from kernel to kernel. The end result is that > if someone had a script that did: > > sysctl vm.zone_reclaim_mode=1 > > This script would have gone from enalbing node reclaim for clean > unmapped pages to writing out pages during node reclaim after the > commit in question. That's not great. > > Put the bits back the way they were and add a comment so something > like this is a bit harder to do again. Update the documentation to > make it clear that the first bit is ignored. > > Signed-off-by: Dave Hansen > Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") > Reviewed-by: Ben Widawsky > Acked-by: David Rientjes > Acked-by: Christoph Lameter > Cc: Alex Shi > Cc: Daniel Wagner > Cc: "Tobin C. Harding" > Cc: Christoph Lameter > Cc: Andrew Morton > Cc: Huang Ying > Cc: Dan Williams > Cc: Qian Cai > Cc: Daniel Wagner > Cc: osalvador > Cc: stable@vger.kernel.org Reviewed-by: Oscar Salvador > > -- > > Changes from v2: > * Update description to indicate that bit0 was used for clean > unmapped page node reclaim. > --- > > b/Documentation/admin-guide/sysctl/vm.rst | 10 +++++----- > b/mm/vmscan.c | 9 +++++++-- > 2 files changed, 12 insertions(+), 7 deletions(-) > > diff -puN Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi Documentation/admin-guide/sysctl/vm.rst > --- a/Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-old-zone_reclaim_mode-abi 2021-01-25 16:23:06.048866718 -0800 > +++ b/Documentation/admin-guide/sysctl/vm.rst 2021-01-25 16:23:06.056866718 -0800 > @@ -978,11 +978,11 @@ that benefit from having their data cach > left disabled as the caching effect is likely to be more important than > data locality. > > -zone_reclaim may be enabled if it's known that the workload is partitioned > -such that each partition fits within a NUMA node and that accessing remote > -memory would cause a measurable performance reduction. The page allocator > -will then reclaim easily reusable pages (those page cache pages that are > -currently not used) before allocating off node pages. > +Consider enabling one or more zone_reclaim mode bits if it's known that the > +workload is partitioned such that each partition fits within a NUMA node > +and that accessing remote memory would cause a measurable performance > +reduction. The page allocator will take additional actions before > +allocating off node pages. > > Allowing zone reclaim to write out pages stops processes that are > writing large amounts of data from dirtying pages on other nodes. Zone > diff -puN mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi mm/vmscan.c > --- a/mm/vmscan.c~mm-vmscan-restore-old-zone_reclaim_mode-abi 2021-01-25 16:23:06.052866718 -0800 > +++ b/mm/vmscan.c 2021-01-25 16:23:06.057866718 -0800 > @@ -4086,8 +4086,13 @@ module_init(kswapd_init) > */ > int node_reclaim_mode __read_mostly; > > -#define RECLAIM_WRITE (1<<0) /* Writeout pages during reclaim */ > -#define RECLAIM_UNMAP (1<<1) /* Unmap pages during reclaim */ > +/* > + * These bit locations are exposed in the vm.zone_reclaim_mode sysctl > + * ABI. New bits are OK, but existing bits can never change. > + */ > +#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ > +#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ > +#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */ > > /* > * Priority for NODE_RECLAIM. This determines the fraction of pages > _ > -- Oscar Salvador SUSE L3