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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 81A42C433E6 for ; Sun, 30 Aug 2020 10:18:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A8F12078D for ; Sun, 30 Aug 2020 10:18:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Bbk5s4ux" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728807AbgH3KSt (ORCPT ); Sun, 30 Aug 2020 06:18:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726406AbgH3KSo (ORCPT ); Sun, 30 Aug 2020 06:18:44 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7F799C061573 for ; Sun, 30 Aug 2020 03:18:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=/GAo2Idg5PG00N2nZbQoR5pf/FedffQ77BrAr0UiKvs=; b=Bbk5s4uxphj3K3Tda8l/eN8Bum bblVL1iDpSHXsmgyPg0qacB6asEZ8I1i/SC2O7ZLjumo0DpEUUc+jHnnoL/oloRCmxiyZL8OVnHKS g9FJvAWXSuvwikupzUwUdmjWZBC3NgX4xdCf4UOTIO64EwmIhUO512u7rQ8BQB9wijYnIMqagPT4k BHhV82fQpssRTZOnsGC7kZuG1/n8HMgCorkvYJpqFo1E6eGbt6bjfO0GnaWyeF2ipdP9DdTcTumcT na53+jQ/FN44RfRQ9d/92tduh3G+O8O9c4gYEuWjn3uvaDmVUEtlRI0BDvZqsNtjdT0Cc9dqJntAj JTM8Y5Cw==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kCKPn-0006ZT-9V; Sun, 30 Aug 2020 10:18:23 +0000 Date: Sun, 30 Aug 2020 11:18:23 +0100 From: Matthew Wilcox To: Alex Shi Cc: Anshuman Khandual , David Hildenbrand , Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Message-ID: <20200830101823.GY14765@casper.infradead.org> References: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> <01c846d4-2fe4-eeef-6c79-e71fda1f9a39@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <01c846d4-2fe4-eeef-6c79-e71fda1f9a39@linux.alibaba.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 30, 2020 at 06:14:33PM +0800, Alex Shi wrote: > +++ b/mm/page_alloc.c > @@ -532,9 +536,18 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, > mask <<= bitidx; > flags <<= bitidx; > > +#ifdef CONFIG_CPU_V6 > + byte = (unsigned long)READ_ONCE(bitmap[byte_bitidx]); > +#else > byte = READ_ONCE(bitmap[byte_bitidx]); > +#endif > for (;;) { > +#ifdef CONFIG_CPU_V6 > + /* arm v6 has no cmpxchgb function, so still false sharing long word */ > + old_byte = cmpxchg((unsigned long*)&bitmap[byte_bitidx], byte, (byte & ~mask) | flags); > +#else > old_byte = cmpxchg(&bitmap[byte_bitidx], byte, (byte & ~mask) | flags); > +#endif Good grief, no. Either come up with an appropriate abstraction or abandon this patch. We can't possibly put this kind of ifdef in the memory allocator!