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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 37F6AC11D02 for ; Thu, 20 Feb 2020 07:52:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF73A24656 for ; Thu, 20 Feb 2020 07:52:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582185144; bh=FVOkIiq9sMU/f2sNfTeRH0KGRCeRtmFxujtwgW3jYQM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=l6Al/QGT/p7kymSlCVaHVkcCBivcdEfdABuZajsO7jUgHKTiK1E9/2hcLNvwK9sVk XrQsavB+14o9A4rxmNfk5nVp9VWfREqU12m3J1SY5PIlHJcwQ4HPLPj9Sa+ZZr+f3I eE9+nUivBGsTVyaFH8+DTz8bRr+/ukPyMg/UTmKc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727021AbgBTHwW (ORCPT ); Thu, 20 Feb 2020 02:52:22 -0500 Received: from mail-wr1-f54.google.com ([209.85.221.54]:35446 "EHLO mail-wr1-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726248AbgBTHwW (ORCPT ); Thu, 20 Feb 2020 02:52:22 -0500 Received: by mail-wr1-f54.google.com with SMTP id w12so3495407wrt.2 for ; Wed, 19 Feb 2020 23:52:21 -0800 (PST) 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:message-id:references :mime-version:content-disposition:in-reply-to; bh=BRUOLe+9hQR/ITm5+YG7M6svLA53jZ3MH/HgtB82Z1U=; b=UzHODRAOVzuGLIaKhJ0IGBwxkoAWWFh0epkV45gdikvOj24gtp7EAWZaDCtSCgFrw3 SHq/B6fYWbsOPH356eugFb8U9/9p5392UKII6vEf0ZnTySF+hj+5rsHRARlXBfVBaC4y zIHpyDMTrQX490MNxgABnjWVRXuWf6ADbpwjxbzGrXN4+lffy6LLvYUS19nZIJ0ziF/s OIZCAMyzKqCnR5As6pDx9mhIAGapuZ9Hgk3Pl3ExMVB0IOzEuJX2W3j6UuB91qJMY5ua 1H7dXRTIrLSJ5OVETp8fCm5/x/QQZGczxPsFOg2NeSdor0WucJPto51eeRpU+V9gUgrT dtgg== X-Gm-Message-State: APjAAAVw1UFrpg8aKC7owj3bgdFZv+7zsA5zmsWWSWlkMfOC4isUlzCw 5jbBpGwbCtTS6WAA6geKn4Q= X-Google-Smtp-Source: APXvYqyhlff/LxgRNqOws+WVTd2HA+haEntq07ZgsqFyewbboJqON2lpO85QAYD69p8fjfC1Fzg7xg== X-Received: by 2002:adf:f64b:: with SMTP id x11mr40043422wrp.355.1582185140366; Wed, 19 Feb 2020 23:52:20 -0800 (PST) Received: from localhost (ip-37-188-133-21.eurotel.cz. [37.188.133.21]) by smtp.gmail.com with ESMTPSA id a8sm3198701wmc.20.2020.02.19.23.52.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Feb 2020 23:52:19 -0800 (PST) Date: Thu, 20 Feb 2020 08:52:18 +0100 From: Michal Hocko To: Andrew Morton Cc: Wei Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, rientjes@google.com Subject: Re: [Patch v4] mm/vmscan.c: remove cpu online notification for now Message-ID: <20200220075218.GA20509@dhcp22.suse.cz> References: <20200218224422.3407-1-richardw.yang@linux.intel.com> <20200219120810.c7677fa58594f5423549f59d@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219120810.c7677fa58594f5423549f59d@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 19-02-20 12:08:10, Andrew Morton wrote: > On Wed, 19 Feb 2020 06:44:22 +0800 Wei Yang wrote: > > > kswapd kernel thread starts either with a CPU affinity set to the full > > cpu mask of its target node or without any affinity at all if the node > > is CPUless. There is a cpu hotplug callback (kswapd_cpu_online) that > > implements an elaborate way to update this mask when a cpu is onlined. > > > > It is not really clear whether there is any actual benefit from this > > scheme. Completely CPU-less NUMA nodes rarely gain a new CPU during > > runtime. > > This is the case across all platforms, all architectures, all users for > the next N years? I'm surprised that we know this with sufficient > confidence. Can you explain how you came to make this assertion? CPUless NUMA nodes are quite rare - mostly ppc with crippled LPARs. I am not aware those would dynamically get CPUs for those nodes later in the runtime. Maybe they do but we would like to learn about that. A missing cpu mask is not going cause any fatal problems anyway. As the changelog states the callback can be reintroduced with a sign of testing and usecase description. I prefer we drop this code in the mean time as the benefit is not really clear or testable. > > Drop the code for that reason. If there is a real usecase then > > we can resurrect and simplify the code. -- Michal Hocko SUSE Labs