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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,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 9A362C11D12 for ; Thu, 20 Feb 2020 17:04:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5F02920722 for ; Thu, 20 Feb 2020 17:04:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RGnBeupn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5F02920722 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0F1086B0072; Thu, 20 Feb 2020 12:04:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0A1FE6B0081; Thu, 20 Feb 2020 12:04:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EF8346B0082; Thu, 20 Feb 2020 12:04:08 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0039.hostedemail.com [216.40.44.39]) by kanga.kvack.org (Postfix) with ESMTP id D7C796B0072 for ; Thu, 20 Feb 2020 12:04:08 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 69534989D for ; Thu, 20 Feb 2020 17:04:08 +0000 (UTC) X-FDA: 76511128176.04.trail55_23f7e23a29130 X-HE-Tag: trail55_23f7e23a29130 X-Filterd-Recvd-Size: 4524 Received: from mail-ed1-f65.google.com (mail-ed1-f65.google.com [209.85.208.65]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Feb 2020 17:04:07 +0000 (UTC) Received: by mail-ed1-f65.google.com with SMTP id c7so2508351edu.2 for ; Thu, 20 Feb 2020 09:04:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=nvdgQUVfRWdhk7IIxKIGzF9ura73FetwX0VHEX0nREE=; b=RGnBeupnO+gVMNXkgEdz6xF3Yi8xjYLf28C7kmJZbCp/KFVl0w6cwhb4aY9TegxhNz PC2blYcXwq9xna3dmHt6H7tOMG5jBLyaPwl1pHKf4CaYKMNRwe39XNdxk/7A72g4lvsh rkU85kltRa30/4PmfNhOS2Z8Rcs1Op1ALWzFBBY5ABZYnMjx1F5rR2qauxDPHgp19dmI KuUq6qUUeOpJ8RQYLIWjasTeIU0jc7tMQ0tnGIRyxpmvDhp5iT9DyfFZ+e15hxowm8Rt gvcBvRC6kh0+V5RpykIMk7IONdRYKQY6YjPzgF5g8ssgSV+GvfMAihN+Nr8kFiIOS4D/ LeVw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=nvdgQUVfRWdhk7IIxKIGzF9ura73FetwX0VHEX0nREE=; b=IiEPNxvW5se0TF4V2PZAva1rmeknpq9X+6Ubs2eumfWwKr3/Xh4wGSNS0R6KacsmMs Wgpy6kGF+cUcndJMRMR0vzQCdj/+bkUJIU0QW9pMQye+OE/bw3sYuobsXnDjyeX4J/4Y soB4vlSB7pVkHRNWKO7uKFIF0mGkiYCkNbhb1qprC2foe2pQTIgg6mW3pO9kskSXJufp 5sDzYrtfkpIszDxVrFbth14GsGjkPk8PCARngkUBBtuLpMbjEAdcL3N/6l0GblsuTFAK H0uhq4dLoIU+5Q9jKoLRlTgMIyvkpOZ2TKuBRVxeYcuC1HAvM6aHM4vxlIPEY1yspBr9 d1Tw== X-Gm-Message-State: APjAAAXhS28L5nXNP7A198omBr28aoJBjiq2PvLMwIcwL97jZ0EECCSz qf68VLKt4J33YPgG3WWwJ2Im/gPQBoqO88HIims= X-Google-Smtp-Source: APXvYqzDKRPRb1AfMfvE+R1DjelsaP1oPwnUkKn8biKIQS9+YWs9RuQ9kxVdlWudPc9yopXNmnx4HuBlCiSkQMqZ73U= X-Received: by 2002:a05:6402:17aa:: with SMTP id j10mr27781546edy.256.1582218245755; Thu, 20 Feb 2020 09:04:05 -0800 (PST) MIME-Version: 1.0 References: <20200218224422.3407-1-richardw.yang@linux.intel.com> <20200219120810.c7677fa58594f5423549f59d@linux-foundation.org> <20200220075218.GA20509@dhcp22.suse.cz> In-Reply-To: <20200220075218.GA20509@dhcp22.suse.cz> From: Yang Shi Date: Thu, 20 Feb 2020 09:03:52 -0800 Message-ID: Subject: Re: [Patch v4] mm/vmscan.c: remove cpu online notification for now To: Michal Hocko Cc: Andrew Morton , Wei Yang , Linux MM , Linux Kernel Mailing List , David Rientjes Content-Type: text/plain; charset="UTF-8" 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 Wed, Feb 19, 2020 at 11:52 PM Michal Hocko wrote: > > 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. Persistent memory nodes are CPUless nodes. But, I don't think they would get any CPU online later in the runtime. > > 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 >