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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 E5AFFC433E9 for ; Wed, 30 Dec 2020 14:20:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B77232220B for ; Wed, 30 Dec 2020 14:20:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726600AbgL3OUI (ORCPT ); Wed, 30 Dec 2020 09:20:08 -0500 Received: from mga05.intel.com ([192.55.52.43]:64455 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725814AbgL3OUH (ORCPT ); Wed, 30 Dec 2020 09:20:07 -0500 IronPort-SDR: A2bRSNflKh5UXxgCiLXDrERS41dEjd75zbjOc9hdkpTieimqORLjWwmCe8WncHM6jSSKuE1Rdr ne241raGa3ZQ== X-IronPort-AV: E=McAfee;i="6000,8403,9849"; a="261359892" X-IronPort-AV: E=Sophos;i="5.78,461,1599548400"; d="scan'208";a="261359892" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Dec 2020 06:19:26 -0800 IronPort-SDR: tmOl3Z62Uo84jH8hAJiYOeYTECaUdq/2xEvydyjaDffdtZnffmZMTE+4w4FYMqdEf41sOtYtCh fHlYantPHPCw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.78,461,1599548400"; d="scan'208";a="395850007" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.147.98]) by fmsmga002.fm.intel.com with ESMTP; 30 Dec 2020 06:19:23 -0800 Date: Wed, 30 Dec 2020 22:19:23 +0800 From: Feng Tang To: Roman Gushchin Cc: Andrew Morton , Michal Hocko , Johannes Weiner , Vladimir Davydov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, andi.kleen@intel.com, tim.c.chen@intel.com, dave.hansen@intel.com, ying.huang@intel.com Subject: Re: [PATCH 1/2] mm: page_counter: relayout structure to reduce false sharing Message-ID: <20201230141923.GA43248@shbuild999.sh.intel.com> References: <1609252514-27795-1-git-send-email-feng.tang@intel.com> <20201229165642.GA371241@carbon.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201229165642.GA371241@carbon.dhcp.thefacebook.com> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 29, 2020 at 08:56:42AM -0800, Roman Gushchin wrote: > On Tue, Dec 29, 2020 at 10:35:13PM +0800, Feng Tang wrote: > > When checking a memory cgroup related performance regression [1], > > from the perf c2c profiling data, we found high false sharing for > > accessing 'usage' and 'parent'. > > > > On 64 bit system, the 'usage' and 'parent' are close to each other, > > and easy to be in one cacheline (for cacheline size == 64+ B). 'usage' > > is usally written, while 'parent' is usually read as the cgroup's > > hierarchical counting nature. > > > > So move the 'parent' to the end of the structure to make sure they > > are in different cache lines. > > > > Following are some performance data with the patch, against > > v5.11-rc1, on several generations of Xeon platforms. Most of the > > results are improvements, with only one malloc case on one platform > > shows a -4.0% regression. Each category below has several subcases > > run on different platform, and only the worst and best scores are > > listed: > > > > fio: +1.8% ~ +8.3% > > will-it-scale/malloc1: -4.0% ~ +8.9% > > will-it-scale/page_fault1: no change > > will-it-scale/page_fault2: +2.4% ~ +20.2% > > > > [1].https://lore.kernel.org/lkml/20201102091543.GM31092@shao2-debian/ > > Signed-off-by: Feng Tang > > Cc: Roman Gushchin > > Cc: Johannes Weiner > > --- > > include/linux/page_counter.h | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h > > index 85bd413..6795913 100644 > > --- a/include/linux/page_counter.h > > +++ b/include/linux/page_counter.h > > @@ -12,7 +12,6 @@ struct page_counter { > > unsigned long low; > > unsigned long high; > > unsigned long max; > > - struct page_counter *parent; > > > > /* effective memory.min and memory.min usage tracking */ > > unsigned long emin; > > @@ -27,6 +26,14 @@ struct page_counter { > > /* legacy */ > > unsigned long watermark; > > unsigned long failcnt; > > + > > + /* > > + * 'parent' is placed here to be far from 'usage' to reduce > > + * cache false sharing, as 'usage' is written mostly while > > + * parent is frequently read for cgroup's hierarchical > > + * counting nature. > > + */ > > + struct page_counter *parent; > > }; > > LGTM! > > Reviewed-by: Roman Gushchin Thanks for the review! > I wonder if we have the same problem with min/low/high/max? > Maybe try to group all mostly-read-only fields (min, low, high, > max and parent) and separate them with some padding? Yep, we thought about it too. From current perf c2c profiling data, I haven't noticed obvious hot spots of false sharing for min/low/high/max (which are read mostly). For padding, we had some proposal before, current page_counter for 64 bits platform is 112 bytes, padding to 2 cacheline will only cost 16 bytes more. If this is fine, I can send another patch or folder it to this one. Thanks, Feng > Thank you!