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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 19B54C433E0 for ; Mon, 29 Jun 2020 06:52:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CB2A323135 for ; Mon, 29 Jun 2020 06:52:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Sq69yB7N" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB2A323135 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5EDAF6B0007; Mon, 29 Jun 2020 02:52:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5797A6B000A; Mon, 29 Jun 2020 02:52:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 440F26B000C; Mon, 29 Jun 2020 02:52:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id 276066B0007 for ; Mon, 29 Jun 2020 02:52:13 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id D4D6E8248047 for ; Mon, 29 Jun 2020 06:52:12 +0000 (UTC) X-FDA: 76981330104.17.train69_411223326e6d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin17.hostedemail.com (Postfix) with ESMTP id A9F5E180D0180 for ; Mon, 29 Jun 2020 06:52:12 +0000 (UTC) X-HE-Tag: train69_411223326e6d X-Filterd-Recvd-Size: 7359 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-2.mimecast.com [207.211.31.81]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Mon, 29 Jun 2020 06:52:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593413531; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hGHkq0oMBoM51wDfqKc/ub/D6arDCkxAo/5yWsL9opI=; b=Sq69yB7NHGZd7lHCEs2QJjcKV/KJCQJ+8lVNPeYEJ3fWIKESJlIrGq5rZwPSNhV7xOzVO1 OQhIIxGAzPRu/Iwh8ntX0X88tX32x8A91UHWob2FuaTMh4TrNqSwU11YZuGGQBe32lT/39 RNPZluiKRKycLfUhpxsSruvRNSjxQIk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-305-0lTKcZHpPomA47JgX2EeaQ-1; Mon, 29 Jun 2020 02:52:09 -0400 X-MC-Unique: 0lTKcZHpPomA47JgX2EeaQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9E8848015FB; Mon, 29 Jun 2020 06:52:07 +0000 (UTC) Received: from localhost (ovpn-13-12.pek2.redhat.com [10.72.13.12]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 813ED5C557; Mon, 29 Jun 2020 06:52:06 +0000 (UTC) Date: Mon, 29 Jun 2020 14:52:03 +0800 From: Baoquan He To: Dave Hansen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, ben.widawsky@intel.com, alex.shi@linux.alibaba.com, dwagner@suse.de, tobin@kernel.org, cl@linux.com, akpm@linux-foundation.org, stable@kernel.org Subject: Re: [PATCH] mm/vmscan: restore zone_reclaim_mode ABI Message-ID: <20200629065203.GJ3346@MiWiFi-R3L-srv> References: <20200626003459.D8E015CA@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200626003459.D8E015CA@viggo.jf.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Rspamd-Queue-Id: A9F5E180D0180 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 06/25/20 at 05:34pm, 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 evidently stopped caring about RECLAIM_ZONE at some point (or > never cared) and the #define itself was later removed as a cleanup. >From git history, it seems to never care about the RECLAIM_ZONE bit. I think this patch is justified. I have one question about adding back the RECLAIM_ZONE bit. Since we introduced RECLAIM_ZONE in the first place, but never use it, removing it truly may fail some existing script, does it mean we will never have chance to fix/clean up this kind of mess? Do we have possibility to remove it in mainline tree, let distos or stable kernel maintainer take care of the back porting? Like this, any stable kernel after 5.8, or any distrols which chooses post v5.8 kenrel as base won't have this confusion. I am not objecting this patch, just be curious if we have a way to fix/clean up for this type of issue. Thanks Baoquan > Those things by themselves are fine. > > But, 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 > > That script went from doing nothing 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: commit 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") > Acked-by: Ben Widawsky > Cc: Alex Shi > Cc: Daniel Wagner > Cc: "Tobin C. Harding" > Cc: Christoph Lameter > Cc: Andrew Morton > Cc: stable@kernel.org > --- > > b/Documentation/admin-guide/sysctl/vm.rst | 12 ++++++------ > b/mm/vmscan.c | 9 +++++++-- > 2 files changed, 13 insertions(+), 8 deletions(-) > > 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 2020-06-25 17:32:11.559165912 -0700 > +++ b/mm/vmscan.c 2020-06-25 17:32:11.572165912 -0700 > @@ -4090,8 +4090,13 @@ 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_RSVD (1<<0) /* (currently ignored/unused) */ > +#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 > 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 2020-06-25 17:32:11.562165912 -0700 > +++ b/Documentation/admin-guide/sysctl/vm.rst 2020-06-25 17:32:11.572165912 -0700 > @@ -938,7 +938,7 @@ in the system. > This is value OR'ed together of > > = =================================== > -1 Zone reclaim on > +1 (bit currently ignored) > 2 Zone reclaim writes dirty pages out > 4 Zone reclaim swaps pages > = =================================== > @@ -948,11 +948,11 @@ 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 > _ >