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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 5BAC1C433DB for ; Wed, 24 Feb 2021 20:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20BD064E20 for ; Wed, 24 Feb 2021 20:11:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235383AbhBXUKs (ORCPT ); Wed, 24 Feb 2021 15:10:48 -0500 Received: from mail.kernel.org ([198.145.29.99]:33400 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235385AbhBXUJ5 (ORCPT ); Wed, 24 Feb 2021 15:09:57 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id DDE8564F23; Wed, 24 Feb 2021 20:09:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1614197356; bh=6uZAIWo00IIlfca439cq6f0bs6LY/39RlcishU7qFJI=; h=Date:From:To:Subject:In-Reply-To:From; b=S9O5QbeZKjn956bTm527aEuDSv+5HUVYmBTRmRGq6PUGt892WCBjgHCNgiA/lFZtS 8hBD/I4ICCbHqovlrvcQAnEaHvIcNeA8BEQXD2xoTtmwkFl8Ls99ivazAKQOp06Qpt EQKJ39Uizh8yDk4GrrJIGU3Xsjfv+A+IptZe1PKU= Date: Wed, 24 Feb 2021 12:09:15 -0800 From: Andrew Morton To: akpm@linux-foundation.org, alex.shi@linux.alibaba.com, ben.widawsky@intel.com, cai@lca.pw, cl@linux.com, dan.j.williams@intel.com, dave.hansen@linux.intel.com, dwagner@suse.de, linux-mm@kvack.org, mm-commits@vger.kernel.org, osalvador@suse.de, rientjes@google.com, stable@vger.kernel.org, tobin@kernel.org, torvalds@linux-foundation.org, ying.huang@intel.com Subject: [patch 152/173] mm/vmscan: restore zone_reclaim_mode ABI Message-ID: <20210224200915.lASg4FukJ%akpm@linux-foundation.org> In-Reply-To: <20210224115824.1e289a6895087f10c41dd8d6@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Dave Hansen Subject: mm/vmscan: restore zone_reclaim_mode ABI 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. Users surely do not expect the meaning to change from kernel to kernel. The end result is that if someone had a script that did: sysctl vm.zone_reclaim_mode=1 it would have gone from enabling 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. Link: https://lkml.kernel.org/r/20210219172555.FF0CDF23@viggo.jf.intel.com Signed-off-by: Dave Hansen Fixes: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") Reviewed-by: Ben Widawsky Reviewed-by: Oscar Salvador 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: Signed-off-by: Andrew Morton --- Documentation/admin-guide/sysctl/vm.rst | 10 +++++----- mm/vmscan.c | 9 +++++++-- 2 files changed, 12 insertions(+), 7 deletions(-) --- a/Documentation/admin-guide/sysctl/vm.rst~mm-vmscan-restore-zone_reclaim_mode-abi +++ a/Documentation/admin-guide/sysctl/vm.rst @@ -983,11 +983,11 @@ 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 --- a/mm/vmscan.c~mm-vmscan-restore-zone_reclaim_mode-abi +++ a/mm/vmscan.c @@ -4085,8 +4085,13 @@ 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 _