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=-6.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 265E7C433E1 for ; Wed, 19 Aug 2020 07:56:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D0A40207BB for ; Wed, 19 Aug 2020 07:56:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D0A40207BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 75CB18D000A; Wed, 19 Aug 2020 03:56:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 70CF98D0001; Wed, 19 Aug 2020 03:56:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 64CC98D000A; Wed, 19 Aug 2020 03:56:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0179.hostedemail.com [216.40.44.179]) by kanga.kvack.org (Postfix) with ESMTP id 4EB008D0001 for ; Wed, 19 Aug 2020 03:56:13 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 163AA362E for ; Wed, 19 Aug 2020 07:56:13 +0000 (UTC) X-FDA: 77166560226.27.stamp48_56127e227026 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin27.hostedemail.com (Postfix) with ESMTP id E625E3D670 for ; Wed, 19 Aug 2020 07:56:12 +0000 (UTC) X-HE-Tag: stamp48_56127e227026 X-Filterd-Recvd-Size: 2050 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Aug 2020 07:56:12 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 766AA1FB; Wed, 19 Aug 2020 00:56:11 -0700 (PDT) Received: from [10.163.66.190] (unknown [10.163.66.190]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1E0223F6CF; Wed, 19 Aug 2020 00:56:08 -0700 (PDT) Subject: Re: [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags To: Alex Shi , Matthew Wilcox , David Hildenbrand Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> From: Anshuman Khandual Message-ID: <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> Date: Wed, 19 Aug 2020 13:25:38 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E625E3D670 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 08/19/2020 11:17 AM, Alex Shi wrote: > pageblock_flags is used as long, since every pageblock_flags is just 4 > bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags, > that flag setting has to sync in cmpxchg with 7 or 15 other pageblock > flags. It would cause long waiting for sync. > > If we could change the pageblock_flags variable as char, we could use > char size cmpxchg, which just sync up with 2 pageblock flags. it could > relief much false sharing in cmpxchg. Do you have numbers demonstrating claimed performance improvement after this change ?