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=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 D5210C433B4 for ; Wed, 31 Mar 2021 20:42:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4EC9C61073 for ; Wed, 31 Mar 2021 20:42:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EC9C61073 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 79A236B007E; Wed, 31 Mar 2021 16:42:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7496C6B0080; Wed, 31 Mar 2021 16:42:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 59BFC6B0081; Wed, 31 Mar 2021 16:42:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0079.hostedemail.com [216.40.44.79]) by kanga.kvack.org (Postfix) with ESMTP id 39FC36B007E for ; Wed, 31 Mar 2021 16:42:14 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E772D812C for ; Wed, 31 Mar 2021 20:42:13 +0000 (UTC) X-FDA: 77981341746.12.4E9ADD3 Received: from outbound-smtp27.blacknight.com (outbound-smtp27.blacknight.com [81.17.249.195]) by imf29.hostedemail.com (Postfix) with ESMTP id 4045D138 for ; Wed, 31 Mar 2021 20:42:12 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail03.blacknight.ie [81.17.254.16]) by outbound-smtp27.blacknight.com (Postfix) with ESMTPS id 86851CAD36 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) X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 4045D138 X-Stat-Signature: zsoy61xqxrqk3ik3utjz17exwkr9got6 Received-SPF: none (techsingularity.net>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=outbound-smtp27.blacknight.com; client-ip=81.17.249.195 X-HE-DKIM-Result: none/none X-HE-Tag: 1617223332-894956 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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