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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 34079C433B4 for ; Wed, 31 Mar 2021 20:43:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0AA3160551 for ; Wed, 31 Mar 2021 20:43:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236510AbhCaUma (ORCPT ); Wed, 31 Mar 2021 16:42:30 -0400 Received: from outbound-smtp46.blacknight.com ([46.22.136.58]:58713 "EHLO outbound-smtp46.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236637AbhCaUmM (ORCPT ); Wed, 31 Mar 2021 16:42:12 -0400 Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp46.blacknight.com (Postfix) with ESMTPS id 8E85FFAE77 for ; Wed, 31 Mar 2021 21:42:11 +0100 (IST) Received: (qmail 5619 invoked from network); 31 Mar 2021 20:42:11 -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); 31 Mar 2021 20:42:11 -0000 Date: Wed, 31 Mar 2021 21:42:10 +0100 From: Mel Gorman To: Thomas Gleixner Cc: Linux-MM , Linux-RT-Users , LKML , Chuck Lever , Jesper Dangaard Brouer , Matthew Wilcox , Sebastian Andrzej Siewior Subject: Re: [PATCH 2/6] mm/page_alloc: Convert per-cpu list protection to local_lock Message-ID: <20210331204210.GB3697@techsingularity.net> References: <20210329120648.19040-1-mgorman@techsingularity.net> <20210329120648.19040-3-mgorman@techsingularity.net> <877dln640j.ffs@nanos.tec.linutronix.de> <20210331110137.GA3697@techsingularity.net> <871rbv5iel.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <871rbv5iel.ffs@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 31, 2021 at 07:42:42PM +0200, Thomas Gleixner wrote: > On Wed, Mar 31 2021 at 12:01, Mel Gorman wrote: > > On Wed, Mar 31, 2021 at 11:55:56AM +0200, Thomas Gleixner wrote: > > @@ -887,13 +887,11 @@ void cpu_vm_stats_fold(int cpu) > > > > pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu); > > > > - preempt_disable(); > > for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) > > if (pzstats->vm_stat_diff[i]) { > > int v; > > > > - v = pzstats->vm_stat_diff[i]; > > - pzstats->vm_stat_diff[i] = 0; > > + v = this_cpu_xchg(pzstats->vm_stat_diff[i], 0); > > Confused. pzstats is not a percpu pointer. zone->per_cpu_zonestats is. > > But @cpu is not necessarily the current CPU. > I was drinking drain cleaner instead of coffee. The code was also broken to begin with. drain_pages() is draining pagesets of a local or dead CPU. For a local CPU, disabling IRQs prevent an IRQ arriving during the drain, trying to allocate a page and potentially corrupt the local pageset -- ok. zone_pcp_reset is accessing a remote CPUs pageset, freeing the percpu pointer and resetting it to boot_pageset. zone_pcp_reset calling local_irq_save() does not offer any special protection against drain_pages because there are two separate IRQs involved. This particular patch may have no reason to touch zone_pcp_reset, cpu_vm_stats_fold or drain_zonestat at all but I need to think about it more tomorrow. -- Mel Gorman SUSE Labs