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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2BDE0C433ED for ; Wed, 31 Mar 2021 17:47:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E894061042 for ; Wed, 31 Mar 2021 17:47:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233934AbhCaRqw (ORCPT ); Wed, 31 Mar 2021 13:46:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233888AbhCaRqh (ORCPT ); Wed, 31 Mar 2021 13:46:37 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 40AB3C061574; Wed, 31 Mar 2021 10:46:37 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1617212794; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=e6M3oUFoCJof3OrZX7FrHMuqU0uhJPLOBOAa++y2rnM=; b=hnltiqf9FMDvo83gt70IXR/oNXXJWgEcos+iHuSQjczu8qGm5lo4hi6U1iI42+VlvC6FCd jttc6ByhgDH9nBZ8mPYxgPFQEcrJpExZk09rZopS1usU4XD2Ow3cZHmJkWqUr2yTNw55bT z3sI86fINzHBfN3y/erHRuX4oGbDn5LKSU0YMK1W7QqRl+Mj+v4QOAMFGmWsbhAfdbqEhh nGUYR8AAY/FY4Ud5NfiErnxyIjB+zmf2XiHC5gzYCiLm6e+GeeOQNo6VB5YkMlk1h4Wf3C yrPDfE7tbDZrXAE13Dg7qa/e6rLv12gQBWOngyAN5k4zVcAkdmd0rArs0CT4Sg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1617212794; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=e6M3oUFoCJof3OrZX7FrHMuqU0uhJPLOBOAa++y2rnM=; b=6v3WlBROvKSc1tFWP8PmqFrEQJ4eDxGM2AErJ05hwHVrcEFvScQiqsEjfCs9TMayipddT1 rrNb2GPSrmUODkAQ== To: Mel Gorman 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 In-Reply-To: <871rbv5iel.ffs@nanos.tec.linutronix.de> 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> Date: Wed, 31 Mar 2021 19:46:34 +0200 Message-ID: <87y2e343np.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Wed, Mar 31 2021 at 19:42, 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. @cpu _is_ definitely NOT the current CPU as this is invoked from the hotplug callback _after_ @cpu went dead. @cpu is dead and wont update these things concurrently. So I'm even more confused :) Thanks, tglx