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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY 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 DB3B8C433E3 for ; Mon, 17 Aug 2020 09:58:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 79A7F20758 for ; Mon, 17 Aug 2020 09:58:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79A7F20758 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D83496B0005; Mon, 17 Aug 2020 05:58:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D33996B0006; Mon, 17 Aug 2020 05:58:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C489B6B0008; Mon, 17 Aug 2020 05:58:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0148.hostedemail.com [216.40.44.148]) by kanga.kvack.org (Postfix) with ESMTP id AB7596B0005 for ; Mon, 17 Aug 2020 05:58:28 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 6AED8824556B for ; Mon, 17 Aug 2020 09:58:28 +0000 (UTC) X-FDA: 77159610696.06.ship11_561213e27015 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id 3BD5A1004A565 for ; Mon, 17 Aug 2020 09:58:28 +0000 (UTC) X-HE-Tag: ship11_561213e27015 X-Filterd-Recvd-Size: 2116 Received: from out30-42.freemail.mail.aliyun.com (out30-42.freemail.mail.aliyun.com [115.124.30.42]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Mon, 17 Aug 2020 09:58:26 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0U6.NLKV_1597658301; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U6.NLKV_1597658301) by smtp.aliyun-inc.com(127.0.0.1); Mon, 17 Aug 2020 17:58:22 +0800 Date: Mon, 17 Aug 2020 17:58:21 +0800 From: Wei Yang To: Alex Shi Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Message-ID: <20200817095821.GA29756@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> X-Rspamd-Queue-Id: 3BD5A1004A565 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 Sun, Aug 16, 2020 at 11:47:56AM +0800, 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. > If my understanding is correct, CPU reads data in the size of cacheline. Define a variable a char or other, doesn't help on false sharing. Correct me, if not. -- Wei Yang Help you, Help me