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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 50DCAC34031 for ; Tue, 18 Feb 2020 22:38:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DE042173E for ; Tue, 18 Feb 2020 22:38:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726680AbgBRWic (ORCPT ); Tue, 18 Feb 2020 17:38:32 -0500 Received: from mga18.intel.com ([134.134.136.126]:11305 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726415AbgBRWic (ORCPT ); Tue, 18 Feb 2020 17:38:32 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Feb 2020 14:38:31 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,458,1574150400"; d="scan'208";a="434266675" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga005.fm.intel.com with ESMTP; 18 Feb 2020 14:38:29 -0800 Date: Wed, 19 Feb 2020 06:38:49 +0800 From: Wei Yang To: Michal Hocko Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rientjes@google.com Subject: Re: [PATCH] mm/vmscan.c: remove cpu online notification for now Message-ID: <20200218223849.GA25405@richard> Reply-To: Wei Yang References: <20200218004354.24996-1-richardw.yang@linux.intel.com> <20200218084023.GC21113@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218084023.GC21113@dhcp22.suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 18, 2020 at 09:40:23AM +0100, Michal Hocko wrote: >On Tue 18-02-20 08:43:54, Wei Yang wrote: >> The cpu online notification is used to adjust kswapd cpu affinity when a >> NUMA node gains a new CPU. >> >> Since currently we don't see a real runtime configuration like this, >> let's drop this online notification for now. > >This deserves much more explanation IMHO. What would you say about the >following. >" >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. Drop the code for that reason. If there is a real usecase then >we can resurrect and simplify the code. >" More better :-) Thanks >> >> Suggested-by: Michal Hocko >> Signed-off-by: Wei Yang > >Acked-by: Michal Hocko > >> >> --- >> v3: >> * remove the cpu online notification suggested by Michal >> v2: >> * rephrase the changelog >> --- >> mm/vmscan.c | 27 +-------------------------- >> 1 file changed, 1 insertion(+), 26 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 665f33258cd7..a4fdf3dc8887 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -4023,27 +4023,6 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim) >> } >> #endif /* CONFIG_HIBERNATION */ >> >> -/* It's optimal to keep kswapds on the same CPUs as their memory, but >> - not required for correctness. So if the last cpu in a node goes >> - away, we get changed to run anywhere: as the first one comes back, >> - restore their cpu bindings. */ >> -static int kswapd_cpu_online(unsigned int cpu) >> -{ >> - int nid; >> - >> - for_each_node_state(nid, N_MEMORY) { >> - pg_data_t *pgdat = NODE_DATA(nid); >> - const struct cpumask *mask; >> - >> - mask = cpumask_of_node(pgdat->node_id); >> - >> - if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) >> - /* One of our CPUs online: restore mask */ >> - set_cpus_allowed_ptr(pgdat->kswapd, mask); >> - } >> - return 0; >> -} >> - >> /* >> * This kswapd start function will be called by init and node-hot-add. >> * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. >> @@ -4083,15 +4062,11 @@ void kswapd_stop(int nid) >> >> static int __init kswapd_init(void) >> { >> - int nid, ret; >> + int nid; >> >> swap_setup(); >> for_each_node_state(nid, N_MEMORY) >> kswapd_run(nid); >> - ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, >> - "mm/vmscan:online", kswapd_cpu_online, >> - NULL); >> - WARN_ON(ret < 0); >> return 0; >> } >> >> -- >> 2.17.1 > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me