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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 08D31C433ED for ; Wed, 14 Apr 2021 15:56:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D07A16112F for ; Wed, 14 Apr 2021 15:56:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352561AbhDNP5S (ORCPT ); Wed, 14 Apr 2021 11:57:18 -0400 Received: from mx2.suse.de ([195.135.220.15]:56588 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351195AbhDNP5Q (ORCPT ); Wed, 14 Apr 2021 11:57:16 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D6F03B0BA; Wed, 14 Apr 2021 15:56:53 +0000 (UTC) Subject: Re: [PATCH 04/11] mm/vmstat: Convert NUMA statistics to basic NUMA counters To: Mel Gorman Cc: Linux-MM , Linux-RT-Users , LKML , Chuck Lever , Jesper Dangaard Brouer , Matthew Wilcox , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Michal Hocko , Oscar Salvador References: <20210407202423.16022-1-mgorman@techsingularity.net> <20210407202423.16022-5-mgorman@techsingularity.net> <7a7ec563-0519-a850-563a-9680a7bd00d3@suse.cz> <20210414151850.GG3697@techsingularity.net> From: Vlastimil Babka Message-ID: Date: Wed, 14 Apr 2021 17:56:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210414151850.GG3697@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On 4/14/21 5:18 PM, Mel Gorman wrote: > On Wed, Apr 14, 2021 at 02:56:45PM +0200, Vlastimil Babka wrote: >> So it seems that this intermediate assignment to zone counters (using >> atomic_long_set() even) is unnecessary and this could mimic sum_vm_events() that >> just does the summation on a local array? >> > > The atomic is unnecessary for sure but using a local array is > problematic because of your next point. IIUC vm_events seems to do fine without a centralized array and handling CPU hot remove at the sime time ... >> And probably a bit more serious is that vm_events have vm_events_fold_cpu() to >> deal with a cpu going away, but after your patch the stats counted on a cpu just >> disapepar from the sums as it goes offline as there's no such thing for the numa >> counters. >> > > That is a problem I missed. Even if zonestats was preserved on > hot-remove, fold_vm_zone_numa_events would not be reading the CPU so > hotplug events jump all over the place. > > So some periodic folding is necessary. I would still prefer not to do it > by time but it could be done only on overflow or when a file like > /proc/vmstat is read. I'll think about it a bit more and see what I come > up with. ... because vm_events_fold_cpu() seems to simply move the stats from the CPU being offlined to the current one. So the same approach should be enough for NUMA stats? > Thanks! >