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,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 3F118C433ED for ; Thu, 15 Apr 2021 10:06:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 150D061249 for ; Thu, 15 Apr 2021 10:06:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232290AbhDOKHS (ORCPT ); Thu, 15 Apr 2021 06:07:18 -0400 Received: from outbound-smtp09.blacknight.com ([46.22.139.14]:54591 "EHLO outbound-smtp09.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232225AbhDOKHR (ORCPT ); Thu, 15 Apr 2021 06:07:17 -0400 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp09.blacknight.com (Postfix) with ESMTPS id 2D9F81C3AEF for ; Thu, 15 Apr 2021 11:06:53 +0100 (IST) Received: (qmail 20158 invoked from network); 15 Apr 2021 10:06:53 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 15 Apr 2021 10:06:52 -0000 Date: Thu, 15 Apr 2021 11:06:50 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Linux-MM , Linux-RT-Users , LKML , Chuck Lever , Jesper Dangaard Brouer , Matthew Wilcox , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Michal Hocko , Oscar Salvador Subject: Re: [PATCH 04/11] mm/vmstat: Convert NUMA statistics to basic NUMA counters Message-ID: <20210415100650.GJ3697@techsingularity.net> References: <20210407202423.16022-1-mgorman@techsingularity.net> <20210407202423.16022-5-mgorman@techsingularity.net> <7a7ec563-0519-a850-563a-9680a7bd00d3@suse.cz> <20210414151850.GG3697@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Wed, Apr 14, 2021 at 05:56:53PM +0200, Vlastimil Babka wrote: > 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 ... > The vm_events are more global in nature. They are not reported to userspace on a per-zone (/proc/zoneinfo) basis or per-node (/sys/devices/system/node/node*/numastat) basis so they are not equivalent. > >> 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? > Yes, or at least very similar. -- Mel Gorman SUSE Labs