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=-11.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLACK,URIBL_BLOCKED, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no 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 AAB3FC433E0 for ; Wed, 1 Jul 2020 20:03:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A79C20760 for ; Wed, 1 Jul 2020 20:03:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="KypgvuN8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726927AbgGAUDY (ORCPT ); Wed, 1 Jul 2020 16:03:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46206 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726021AbgGAUDX (ORCPT ); Wed, 1 Jul 2020 16:03:23 -0400 Received: from mail-pg1-x542.google.com (mail-pg1-x542.google.com [IPv6:2607:f8b0:4864:20::542]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77B41C08C5C1 for ; Wed, 1 Jul 2020 13:03:22 -0700 (PDT) Received: by mail-pg1-x542.google.com with SMTP id d4so12238231pgk.4 for ; Wed, 01 Jul 2020 13:03:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=DG/OiDzZKYxcN7tgph7u8U8cnXnzZZZ9acgCYJ83YwI=; b=KypgvuN8A6GvTF5CN3Jkyl+A7/LMTi++GIYEZVAvfQi8Ot5Tt64QQjwC4jI0Hirc63 iBxqDmcC8hQBSMpQTuj32vL9Fuu9LG1Pvcyb6jm8sCChD5g6kENuDDiDPl8siCk5ItI1 9BNxJ9NPtSYOUcfNQUih4K3sxuEZfSR932DUdWkGiN8GefDd6KVkKhnbNa1N8U0k19js aJXpTsMFQ0iIxT9bJ1RKG5ebx8FJH3c6RukiwJ5CMFoJHAlM/naxjBXIoTyLtVzwDz9L cZM71EnZcykycNMhxQWdJwYTAX11OSuRavVKU054lU719RM88tvgtw45NLNa/pVDas6l kvvw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=DG/OiDzZKYxcN7tgph7u8U8cnXnzZZZ9acgCYJ83YwI=; b=CCpfHLIT4j239/Ee5zeJ+mneKhagPoWjHlCSN0G0HcaBp5SwYi0Mc/bKXR3b2ovd9u 7QIjgpyA2JlAqeQPt4PIC3NkrFRjsvMlTq+OfuY/AuBTyQ4SnuBiVcq71DkNTUi6AeX7 oHfmN15Pxky3sAj2e2FaRR3jeRgx39EDbyEAthTIG7dbX3jCUTDYzfjFV9jIuPFv2sTh wYx3VFN1sH8VS4C/fEwq/qf0GrDTnnUJZce/369kiFj8UWMVBGW9eal7RvLYWqIFsQQP xof7Q3Ju9YgLMZmEJs0kCG+1/ReWvERTdjDyi+LyYqq5IkRJicSyYXqvzVYQ187gq/No 2geg== X-Gm-Message-State: AOAM531g8iv2ynSrpG8Q2HMbIq6Gg/S16YOzW4fsH6Le9ncjej8R1/b7 dsrXejn+0Q83tn6fvV90mjyGoA== X-Google-Smtp-Source: ABdhPJzS45NkXiunLsIzMQvukb9uRBU3YXdQl00MI74iobOT3CgQ4L0Gm7O7Mii1eRv3hj+zNHOjbw== X-Received: by 2002:aa7:86c1:: with SMTP id h1mr12889126pfo.175.1593633801894; Wed, 01 Jul 2020 13:03:21 -0700 (PDT) Received: from [2620:15c:17:3:4a0f:cfff:fe51:6667] ([2620:15c:17:3:4a0f:cfff:fe51:6667]) by smtp.gmail.com with ESMTPSA id u2sm5954919pfl.21.2020.07.01.13.03.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 13:03:21 -0700 (PDT) Date: Wed, 1 Jul 2020 13:03:20 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com 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, ying.huang@intel.com, dan.j.williams@intel.com, cai@lca.pw, stable@vger.kernel.org Subject: Re: [PATCH 1/3] mm/vmscan: restore zone_reclaim_mode ABI In-Reply-To: <20200701152623.384AF0A7@viggo.jf.intel.com> Message-ID: References: <20200701152621.D520E62B@viggo.jf.intel.com> <20200701152623.384AF0A7@viggo.jf.intel.com> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 1 Jul 2020, 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 > > 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: 648b5cf368e0 ("mm/vmscan: remove unused RECLAIM_OFF/RECLAIM_ZONE") > Cc: Ben Widawsky > 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: stable@vger.kernel.org Acked-by: David Rientjes