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,UNPARSEABLE_RELAY,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 00F35C433DF for ; Wed, 19 Aug 2020 08:37:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CBCEA207FF for ; Wed, 19 Aug 2020 08:37:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726715AbgHSIhz (ORCPT ); Wed, 19 Aug 2020 04:37:55 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:33717 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726414AbgHSIhx (ORCPT ); Wed, 19 Aug 2020 04:37:53 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07425;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0U6DSz3L_1597826267; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U6DSz3L_1597826267) by smtp.aliyun-inc.com(127.0.0.1); Wed, 19 Aug 2020 16:37:48 +0800 Subject: Re: [PATCH v2 2/2] mm/pageblock: remove false sharing in pageblock_flags To: David Hildenbrand , Anshuman Khandual , Matthew Wilcox Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> <1597816075-61091-2-git-send-email-alex.shi@linux.alibaba.com> <715f1588-9cd5-b845-51a5-ca58549c4d28@arm.com> <0dc33af2-4d2d-9531-03fa-d26654ab79fb@redhat.com> From: Alex Shi Message-ID: <420c8091-f0c7-f7e6-be95-85d81f877aae@linux.alibaba.com> Date: Wed, 19 Aug 2020 16:36:36 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <0dc33af2-4d2d-9531-03fa-d26654ab79fb@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2020/8/19 下午4:13, David Hildenbrand 写道: > On 19.08.20 10:09, Alex Shi wrote: >> >> >> 在 2020/8/19 下午3:57, Anshuman Khandual 写道: >>> >>> >>> On 08/19/2020 11:17 AM, Alex Shi wrote: >>>> Current pageblock_flags is only 4 bits, so it has to share a char size >>>> in cmpxchg when get set, the false sharing cause perf drop. >>>> >>>> If we incrase the bits up to 8, false sharing would gone in cmpxchg. and >>>> the only cost is half char per pageblock, which is half char per 128MB >>>> on x86, 4 chars in 1 GB. >>> >>> Agreed that increase in memory utilization is negligible here but does >>> this really improve performance ? >>> >> >> It's no doubt in theory. and it would had a bad impact according to >> commit e380bebe4771548 mm, compaction: keep migration source private to a single The above commit is a good disproof, the false sharing caused performance issue, and need using a lock protect cmpxchg, the instruction was designed for lockless using. The false sharing, it was a trouble, and would trouble again sometime. Thanks Alex >> >> but I do have some problem in running thpscale/mmtest. I'd like to see if anyone >> could give a try. >> >> BTW, I naturally hate the false sharing even it's in theory. Anyone who doesn't? :) > > I hate wasting memory, even if it's just a little bit, anyone who > doesn't? ;) > >