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 164ACC433E0 for ; Fri, 22 May 2020 15:17:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D9B96205CB for ; Fri, 22 May 2020 15:17:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D9B96205CB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7FBB080008; Fri, 22 May 2020 11:17:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7AB3A80007; Fri, 22 May 2020 11:17:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6C0D780008; Fri, 22 May 2020 11:17:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0227.hostedemail.com [216.40.44.227]) by kanga.kvack.org (Postfix) with ESMTP id 513E780007 for ; Fri, 22 May 2020 11:17:17 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 010FC8248076 for ; Fri, 22 May 2020 15:17:16 +0000 (UTC) X-FDA: 76844708472.27.brake91_5c9f7b5996e1a X-HE-Tag: brake91_5c9f7b5996e1a X-Filterd-Recvd-Size: 2194 Received: from Galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Fri, 22 May 2020 15:17:16 +0000 (UTC) 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> 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 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