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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 2BAAEC5519F for ; Fri, 20 Nov 2020 13:20:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C163622264 for ; Fri, 20 Nov 2020 13:20:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="c3Bzg8dy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728005AbgKTNTs (ORCPT ); Fri, 20 Nov 2020 08:19:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:45888 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726420AbgKTNTr (ORCPT ); Fri, 20 Nov 2020 08:19:47 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1605878385; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/Z8rc3zQ3crrhBs5Y0c/KBtW/ZSlL91xf2br3FctmXA=; b=c3Bzg8dyM+48ewtHABKwc/R/8OtE7xig6m4MooRi1rs1ATz6SZnS+ugcjfgsidN4rxqUWP u1qQym9EVTrWWdT+abp8yegDmYrmjjRZVPFCPCMS42lveH/LQ12KUZGiPK9+0tQFkKOlKd h6NAHSM2BEXpmYQsYZQBIoYNb3kXOVY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 94E0FAA4F; Fri, 20 Nov 2020 13:19:45 +0000 (UTC) Date: Fri, 20 Nov 2020 14:19:44 +0100 From: Michal Hocko To: Feng Tang Cc: Xing Zhengjun , Waiman Long , Linus Torvalds , Andrew Morton , Shakeel Butt , Chris Down , Johannes Weiner , Roman Gushchin , Tejun Heo , Vladimir Davydov , Yafang Shao , LKML , lkp@lists.01.org, lkp@intel.com, zhengjun.xing@intel.com, ying.huang@intel.com Subject: Re: [LKP] Re: [mm/memcg] bd0b230fe1: will-it-scale.per_process_ops -22.7% regression Message-ID: <20201120131944.GP3200@dhcp22.suse.cz> References: <20201102091543.GM31092@shao2-debian> <20201102092754.GD22613@dhcp22.suse.cz> <82d73ebb-a31e-4766-35b8-82afa85aa047@intel.com> <20201102100247.GF22613@dhcp22.suse.cz> <20201104081546.GB10052@dhcp22.suse.cz> <20201112122844.GA11000@shbuild999.sh.intel.com> <20201112141654.GC12240@dhcp22.suse.cz> <20201113073436.GA113119@shbuild999.sh.intel.com> <20201120114424.GA103521@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120114424.GA103521@shbuild999.sh.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 20-11-20 19:44:24, Feng Tang wrote: > On Fri, Nov 13, 2020 at 03:34:36PM +0800, Feng Tang wrote: > > On Thu, Nov 12, 2020 at 03:16:54PM +0100, Michal Hocko wrote: > > > > > > I add one phony page_counter after the union and re-test, the regression > > > > > > reduced to -1.2%. It looks like the regression caused by the data structure > > > > > > layout change. > > > > > > > > > > Thanks for double checking. Could you try to cache align the > > > > > page_counter struct? If that helps then we should figure which counters > > > > > acks against each other by adding the alignement between the respective > > > > > counters. > > > > > > > > We tried below patch to make the 'page_counter' aligned. > > > > > > > > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h > > > > index bab7e57..9efa6f7 100644 > > > > --- a/include/linux/page_counter.h > > > > +++ b/include/linux/page_counter.h > > > > @@ -26,7 +26,7 @@ struct page_counter { > > > > /* legacy */ > > > > unsigned long watermark; > > > > unsigned long failcnt; > > > > -}; > > > > +} ____cacheline_internodealigned_in_smp; > > > > > > > > and with it, the -22.7% peformance change turns to a small -1.7%, which > > > > confirms the performance bump is caused by the change to data alignment. > > > > > > > > After the patch, size of 'page_counter' increases from 104 bytes to 128 > > > > bytes, and the size of 'mem_cgroup' increases from 2880 bytes to 3008 > > > > bytes(with our kernel config). Another major data structure which > > > > contains 'page_counter' is 'hugetlb_cgroup', whose size will change > > > > from 912B to 1024B. > > > > > > > > Should we make these page_counters aligned to reduce cacheline conflict? > > > > > > I would rather focus on a more effective mem_cgroup layout. It is very > > > likely that we are just stumbling over two counters here. > > > > > > Could you try to add cache alignment of counters after memory and see > > > which one makes the difference? I do not expect memsw to be the one > > > because that one is used together with the main counter. But who knows > > > maybe the way it crosses the cache line has the exact effect. Hard to > > > tell without other numbers. > > > > I added some alignments change around the 'memsw', but neither of them can > > restore the -22.7%. Following are some log showing how the alignments > > are: > > > > tl: memcg=0x7cd1000 memory=0x7cd10d0 memsw=0x7cd1140 kmem=0x7cd11b0 tcpmem=0x7cd1220 > > t2: memcg=0x7cd0000 memory=0x7cd00d0 memsw=0x7cd0140 kmem=0x7cd01c0 tcpmem=0x7cd0230 > > > > So both of the 'memsw' are aligned, but t2's 'kmem' is aligned while > > t1's is not. > > > > I will check more on the perf data about detailed hotspots. > > Some more check updates about it: > > Waiman's patch is effectively removing one 'struct page_counter' between > 'memory' and "memsw'. And the mem_cgroup is: > > struct mem_cgroup { > > ... > > struct page_counter memory; /* Both v1 & v2 */ > > union { > struct page_counter swap; /* v2 only */ > struct page_counter memsw; /* v1 only */ > }; > > /* Legacy consumer-oriented counters */ > struct page_counter kmem; /* v1 only */ > struct page_counter tcpmem; /* v1 only */ > > ... > ... > > MEMCG_PADDING(_pad1_); > > atomic_t moving_account; > struct task_struct *move_lock_task; > > ... > }; > > > I do experiments by inserting a 'page_counter' between 'memory' > and the 'MEMCG_PADDING(_pad1_)', no matter where I put it, the > benchmark result can be recovered from 145K to 185K, which is > really confusing, as adding a 'page_counter' right before the > '_pad1_' doesn't change cache alignment of any members. Have you checked the result of pahole before and after your modification whether something stands out? Btw. is this reproducible an different CPU models? -- Michal Hocko SUSE Labs