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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 56E5CC433DF for ; Fri, 22 May 2020 15:17:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 26FB62065C for ; Fri, 22 May 2020 15:17:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730234AbgEVPRM (ORCPT ); Fri, 22 May 2020 11:17:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729929AbgEVPRM (ORCPT ); Fri, 22 May 2020 11:17:12 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E88F7C061A0E for ; Fri, 22 May 2020 08:17:11 -0700 (PDT) Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1jc9Q1-0007ZR-HW; Fri, 22 May 2020 17:17:05 +0200 Date: Fri, 22 May 2020 17:17:05 +0200 From: "Sebastian A. Siewior" To: Peter Zijlstra Cc: "Ahmed S. Darwish" , Ingo Molnar , Will Deacon , Thomas Gleixner , "Paul E. McKenney" , Steven Rostedt , LKML , Andrew Morton , Konstantin Khlebnikov , linux-mm@kvack.org Subject: Re: [PATCH v1 02/25] mm/swap: Don't abuse the seqcount latching API Message-ID: <20200522151705.vwfua5a4lhzcagea@linutronix.de> References: <20200519214547.352050-1-a.darwish@linutronix.de> <20200519214547.352050-3-a.darwish@linutronix.de> <20200522145707.GO325280@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200522145707.GO325280@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-22 16:57:07 [+0200], Peter Zijlstra wrote: > > @@ -725,21 +735,48 @@ void lru_add_drain_all(void) > > if (WARN_ON(!mm_percpu_wq)) > > return; > > > > > + this_gen = READ_ONCE(lru_drain_gen); > > + smp_rmb(); > > this_gen = smp_load_acquire(&lru_drain_gen); > > > > mutex_lock(&lock); > > > > /* > > + * (C) Exit the draining operation if a newer generation, from another > > + * lru_add_drain_all(), was already scheduled for draining. Check (A). > > */ > > + if (unlikely(this_gen != lru_drain_gen)) > > goto done; > > > > > + WRITE_ONCE(lru_drain_gen, lru_drain_gen + 1); > > + smp_wmb(); > > You can leave this smp_wmb() out and rely on the smp_mb() implied by > queue_work_on()'s test_and_set_bit(). This is to avoid smp_store_release() ? Sebastian