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=-6.2 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 BD5E5C433E1 for ; Sun, 16 Aug 2020 14:20:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 81086207FF for ; Sun, 16 Aug 2020 14:20:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 81086207FF 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 0C10D6B0002; Sun, 16 Aug 2020 10:20:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 073736B0005; Sun, 16 Aug 2020 10:20:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ED22D6B0006; Sun, 16 Aug 2020 10:20:48 -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 D7B126B0002 for ; Sun, 16 Aug 2020 10:20:48 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 86EB0824556B for ; Sun, 16 Aug 2020 14:20:48 +0000 (UTC) X-FDA: 77156642976.27.art24_2c0213e2700e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin27.hostedemail.com (Postfix) with ESMTP id 5E73D3D663 for ; Sun, 16 Aug 2020 14:20:48 +0000 (UTC) X-HE-Tag: art24_2c0213e2700e X-Filterd-Recvd-Size: 3193 Received: from out4436.biz.mail.alibaba.com (out4436.biz.mail.alibaba.com [47.88.44.36]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Sun, 16 Aug 2020 14:20:47 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01358;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0U5uJ-GC_1597587304; Received: from IT-FVFX43SYHV2H.lan(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U5uJ-GC_1597587304) by smtp.aliyun-inc.com(127.0.0.1); Sun, 16 Aug 2020 22:15:05 +0800 Subject: Re: [PATCH 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags To: David Hildenbrand Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1597549677-7480-1-git-send-email-alex.shi@linux.alibaba.com> From: Alex Shi Message-ID: <89b42892-8257-e3fc-34c9-27d9a470ed79@linux.alibaba.com> Date: Sun, 16 Aug 2020 22:14:08 +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: Content-Type: text/plain; charset=utf-8 X-Rspamd-Queue-Id: 5E73D3D663 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 2020/8/16 =E4=B8=8B=E5=8D=888:16, David Hildenbrand =E5=86=99=E9= =81=93: > On 16.08.20 05:47, 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' flag= s, >> 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. >=20 > Do you have any performance numbers to back your claims? IOW, do we car= e > at all? >=20 >=20 Hi David, Thanks for comments! Not yet, I trace the following commit here, with this commit this hot pat= h looks be resolved. Thanks Alex e380bebe4771548 mm, compaction: keep migration source private to a singl= e compaction instance if (!locked) { locked =3D compact_trylock_irqsave(zone_lru_lock(= zone), &flags, c= c); - if (!locked) + + /* Allow future scanning if the lock is contended= */ + if (!locked) { + clear_pageblock_skip(page); break; + } + + /* Try get exclusive access under lock */ + if (!skip_updated) { + skip_updated =3D true; + if (test_and_set_skip(cc, page, low_pfn)) + goto isolate_abort; + }