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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 79F0CC433E0 for ; Mon, 6 Jul 2020 01:43:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F7EC2070C for ; Mon, 6 Jul 2020 01:43:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728590AbgGFBnT (ORCPT ); Sun, 5 Jul 2020 21:43:19 -0400 Received: from mga18.intel.com ([134.134.136.126]:11124 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728430AbgGFBnS (ORCPT ); Sun, 5 Jul 2020 21:43:18 -0400 IronPort-SDR: ag5V6HbAViY+CkPJE665DDz4HzcJljPD8RH9PfPy42LA7Y3zNr8VzgSd3fVP1NPP2CQ39eAtP5 1iotGj1Of5Pw== X-IronPort-AV: E=McAfee;i="6000,8403,9673"; a="134803047" X-IronPort-AV: E=Sophos;i="5.75,318,1589266800"; d="scan'208";a="134803047" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Jul 2020 18:43:18 -0700 IronPort-SDR: tI7NthIGo8GW+RU/lbxxRFrecLwMUGm2L4cRXYSupUl97TkEau6NhFp69DN4TjqiQNOs1/RH0Z uTeZY0DjHPrQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,318,1589266800"; d="scan'208";a="296850630" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.146.107]) by orsmga002.jf.intel.com with ESMTP; 05 Jul 2020 18:43:13 -0700 Date: Mon, 6 Jul 2020 09:43:13 +0800 From: Feng Tang To: Qian Cai Cc: kernel test robot , Andrew Morton , Michal Hocko , Johannes Weiner , Matthew Wilcox , Mel Gorman , Kees Cook , Luis Chamberlain , Iurii Zaikin , andi.kleen@intel.com, tim.c.chen@intel.com, dave.hansen@intel.com, ying.huang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, lkp@lists.01.org Subject: Re: [mm] 4e2c82a409: ltp.overcommit_memory01.fail Message-ID: <20200706014313.GB66252@shbuild999.sh.intel.com> References: <20200705044454.GA90533@shbuild999.sh.intel.com> <20200705125854.GA66252@shbuild999.sh.intel.com> <20200705155232.GA608@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200705155232.GA608@lca.pw> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 05, 2020 at 11:52:32AM -0400, Qian Cai wrote: > On Sun, Jul 05, 2020 at 08:58:54PM +0800, Feng Tang wrote: > > On Sun, Jul 05, 2020 at 08:15:03AM -0400, Qian Cai wrote: > > > > > > > > > > On Jul 5, 2020, at 12:45 AM, Feng Tang wrote: > > > > > > > > I did reproduce the problem, and from the debugging, this should > > > > be the same root cause as lore.kernel.org/lkml/20200526181459.GD991@lca.pw/ > > > > that loosing the batch cause some accuracy problem, and the solution of > > > > adding some sync is still needed, which is dicussed in > > > > > > Well, before taking any of those patches now to fix the regression, > > > we will need some performance data first. If it turned out the > > > original performance gain is no longer relevant anymore due to this > > > regression fix on top, it is best to drop this patchset and restore > > > that VM_WARN_ONCE, so you can retry later once you found a better > > > way to optimize. > > > > The fix of adding sync only happens when the memory policy is being > > changed to OVERCOMMIT_NEVER, which is not a frequent operation in > > normal cases. > > > > For the performance improvment data both in commit log and 0day report > > https://lore.kernel.org/lkml/20200622132548.GS5535@shao2-debian/ > > it is for the will-it-scale's mmap testcase, which will not runtime > > change memory overcommit policy, so the data should be still valid > > with this fix. > > Well, I would expect people are perfectly reasonable to use > OVERCOMMIT_NEVER for some workloads making it more frequent operations. In my last email, I was not saying OVERCOMMIT_NEVER is not a normal case, but I don't think user will too frequently runtime change the overcommit policy. And the fix patch of syncing 'vm_committed_as' is only called when user calls 'sysctl -w vm.overcommit_memory=2'. > The question is now if any of those regression fixes would now regress > performance of OVERCOMMIT_NEVER workloads or just in-par with the data > before the patchset? For the original patchset, it keeps vm_committed_as unchanged for OVERCOMMIT_NEVER policy and enlarge it for the other 2 loose policies OVERCOMMIT_ALWAYS and OVERCOMMIT_GUESS, and I don't expect the "OVERCOMMIT_NEVER workloads" performance will be impacted. If you have suggetions for this kind of benchmarks, I can test them to better verify the patchset, thanks! - Feng > > Given now this patchset has had so much churn recently, I would think > "should be still valid" is not really the answer we are looking for. > > > > > Thanks, > > Feng > > > >