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 367ABC47089 for ; Thu, 27 May 2021 19:36:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DFBB61028 for ; Thu, 27 May 2021 19:36:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235470AbhE0TiD (ORCPT ); Thu, 27 May 2021 15:38:03 -0400 Received: from mga12.intel.com ([192.55.52.136]:4167 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234187AbhE0Th6 (ORCPT ); Thu, 27 May 2021 15:37:58 -0400 IronPort-SDR: 345uYSbRy8QlE/1/r9uuY3/SHHZmluF3/u2CsCzww05ZtA4JsO/qJjfWjKnjObmes+uOp0AE2I xvhqDcz606XA== X-IronPort-AV: E=McAfee;i="6200,9189,9997"; a="182476009" X-IronPort-AV: E=Sophos;i="5.83,228,1616482800"; d="scan'208";a="182476009" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 May 2021 12:36:24 -0700 IronPort-SDR: tr9HPIJDUJ0IO0vxXlGe01y5nvxI6D2qHeB3tLJ8LTr8SGXywXcoYvxlLcmZvJgvkcDSCyuMBe 8GvQfqsHFNOw== X-IronPort-AV: E=Sophos;i="5.83,228,1616482800"; d="scan'208";a="445162832" Received: from sushilsu-mobl1.amr.corp.intel.com (HELO [10.209.3.242]) ([10.209.3.242]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 May 2021 12:36:23 -0700 Subject: Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs To: Mel Gorman , Andrew Morton Cc: Hillf Danton , Dave Hansen , Vlastimil Babka , Michal Hocko , LKML , Linux-MM , "Tang, Feng" References: <20210525080119.5455-1-mgorman@techsingularity.net> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210525080119.5455-1-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Maybe instead of pretending that cpu-less nodes have one cpu: nr_local_cpus = max(1U, cpumask_weight(cpumask_of_node(zone_to_nid(zone)))); we should just consider them to have *all* the CPUs in the system. Perhaps: nr_local_cpus = cpumask_weight(cpumask_of_node(zone_to_nid(zone))); if (!nr_local_cpus) nr_local_cpus = num_online_cpus(); Even if a system has a silly number of CPUs, the 'high' sizes will still hit a floor at 4*batch: high = max(high, batch << 2); Which doesn't seem too bad, especially considering that CPU-less nodes naturally have less contention.