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 48C75C433E1 for ; Wed, 19 Aug 2020 08:38:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0FC8C20772 for ; Wed, 19 Aug 2020 08:38:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0FC8C20772 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 A817A6B0074; Wed, 19 Aug 2020 04:37:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A327D6B0075; Wed, 19 Aug 2020 04:37:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 947276B0078; Wed, 19 Aug 2020 04:37:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0025.hostedemail.com [216.40.44.25]) by kanga.kvack.org (Postfix) with ESMTP id 7B1BA6B0074 for ; Wed, 19 Aug 2020 04:37:59 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 3E862362C for ; Wed, 19 Aug 2020 08:37:59 +0000 (UTC) X-FDA: 77166665478.19.toad88_3000adb27026 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin19.hostedemail.com (Postfix) with ESMTP id 146111AD1B7 for ; Wed, 19 Aug 2020 08:37:59 +0000 (UTC) X-HE-Tag: toad88_3000adb27026 X-Filterd-Recvd-Size: 3138 Received: from out30-42.freemail.mail.aliyun.com (out30-42.freemail.mail.aliyun.com [115.124.30.42]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Aug 2020 08:37:54 +0000 (UTC) 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 X-Rspamd-Queue-Id: 146111AD1B7 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 Content-Transfer-Encoding: quoted-printable 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: =E5=9C=A8 2020/8/19 =E4=B8=8B=E5=8D=884:13, David Hildenbrand =E5=86=99=E9= =81=93: > On 19.08.20 10:09, Alex Shi wrote: >> >> >> =E5=9C=A8 2020/8/19 =E4=B8=8B=E5=8D=883:57, Anshuman Khandual =E5=86=99= =E9=81=93: >>> >>> >>> On 08/19/2020 11:17 AM, Alex Shi wrote: >>>> Current pageblock_flags is only 4 bits, so it has to share a char si= ze >>>> 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 128= MB >>>> on x86, 4 chars in 1 GB. >>> >>> Agreed that increase in memory utilization is negligible here but doe= s >>> this really improve performance ? >>> >> >> It's no doubt in theory. and it would had a bad impact according to=20 >> commit e380bebe4771548 mm, compaction: keep migration source private = to a single=20 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 l= ockless using. The false sharing, it was a trouble, and would trouble again somet= ime. 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 wh= o doesn't? :) >=20 > I hate wasting memory, even if it's just a little bit, anyone who > doesn't? ;) >=20 >=20