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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 83D92C47087 for ; Fri, 28 May 2021 08:55:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53C95613E3 for ; Fri, 28 May 2021 08:55:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235781AbhE1I5Y (ORCPT ); Fri, 28 May 2021 04:57:24 -0400 Received: from outbound-smtp29.blacknight.com ([81.17.249.32]:36107 "EHLO outbound-smtp29.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234366AbhE1I5W (ORCPT ); Fri, 28 May 2021 04:57:22 -0400 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp29.blacknight.com (Postfix) with ESMTPS id CEA4218E002 for ; Fri, 28 May 2021 09:55:46 +0100 (IST) Received: (qmail 5451 invoked from network); 28 May 2021 08:55:46 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.23.168]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 28 May 2021 08:55:46 -0000 Date: Fri, 28 May 2021 09:55:45 +0100 From: Mel Gorman To: Dave Hansen Cc: Andrew Morton , Hillf Danton , Dave Hansen , Vlastimil Babka , Michal Hocko , LKML , Linux-MM , "Tang, Feng" Subject: Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs Message-ID: <20210528085545.GJ30378@techsingularity.net> References: <20210525080119.5455-1-mgorman@techsingularity.net> <7177f59b-dc05-daff-7dc6-5815b539a790@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <7177f59b-dc05-daff-7dc6-5815b539a790@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 27, 2021 at 12:36:21PM -0700, Dave Hansen wrote: > Hi Mel, > > Feng Tang tossed these on a "Cascade Lake" system with 96 threads and > ~512G of persistent memory and 128G of DRAM. The PMEM is in "volatile > use" mode and being managed via the buddy just like the normal RAM. > > The PMEM zones are big ones: > > present 65011712 = 248 G > high 134595 = 525 M > > The PMEM nodes, of course, don't have any CPUs in them. > > With your series, the pcp->high value per-cpu is 69584 pages or about > 270MB per CPU. Scaled up by the 96 CPU threads, that's ~26GB of > worst-case memory in the pcps per zone, or roughly 10% of the size of > the zone. > > I did see quite a few pcp->counts above 60,000, so it's definitely > possible in practice to see the pcps filled up. This was not observed > to cause any actual problems in practice. But, it's still a bit worrisome. > Ok, it does have the potential to trigger early reclaim as pages are stored on remote PCP lists. The problem would be transient because vmstat would drain those pages over time but still, how about this patch on top of the series? --8<-- mm/page_alloc: Split pcp->high across all online CPUs for cpuless nodes Dave Hansen reported the following about Feng Tang's tests on a machine with persistent memory onlined as a DRAM-like device. Feng Tang tossed these on a "Cascade Lake" system with 96 threads and ~512G of persistent memory and 128G of DRAM. The PMEM is in "volatile use" mode and being managed via the buddy just like the normal RAM. The PMEM zones are big ones: present 65011712 = 248 G high 134595 = 525 M The PMEM nodes, of course, don't have any CPUs in them. With your series, the pcp->high value per-cpu is 69584 pages or about 270MB per CPU. Scaled up by the 96 CPU threads, that's ~26GB of worst-case memory in the pcps per zone, or roughly 10% of the size of the zone. This should not cause a problem as such although it could trigger reclaim due to pages being stored on per-cpu lists for CPUs remote to a node. It is not possible to treat cpuless nodes exactly the same as normal nodes but the worst-case scenario can be mitigated by splitting pcp->high across all online CPUs for cpuless memory nodes. Suggested-by: Dave Hansen Signed-off-by: Mel Gorman --- mm/page_alloc.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d708aa14f4ef..af566e97a0f8 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6687,7 +6687,7 @@ static int zone_highsize(struct zone *zone, int batch, int cpu_online) { #ifdef CONFIG_MMU int high; - int nr_local_cpus; + int nr_split_cpus; unsigned long total_pages; if (!percpu_pagelist_high_fraction) { @@ -6710,10 +6710,14 @@ static int zone_highsize(struct zone *zone, int batch, int cpu_online) * Split the high value across all online CPUs local to the zone. Note * that early in boot that CPUs may not be online yet and that during * CPU hotplug that the cpumask is not yet updated when a CPU is being - * onlined. - */ - nr_local_cpus = max(1U, cpumask_weight(cpumask_of_node(zone_to_nid(zone)))) + cpu_online; - high = total_pages / nr_local_cpus; + * onlined. For memory nodes that have no CPUs, split pcp->high across + * all online CPUs to mitigate the risk that reclaim is triggered + * prematurely due to pages stored on pcp lists. + */ + nr_split_cpus = cpumask_weight(cpumask_of_node(zone_to_nid(zone))) + cpu_online; + if (!nr_split_cpus) + nr_split_cpus = num_online_cpus(); + high = total_pages / nr_split_cpus; /* * Ensure high is at least batch*4. The multiple is based on the