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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id x4sm14390623qkl.130.2020.07.05.08.52.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Jul 2020 08:52:38 -0700 (PDT) Date: Sun, 5 Jul 2020 11:52:32 -0400 From: Qian Cai To: Feng Tang 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: <20200705155232.GA608@lca.pw> References: <20200705044454.GA90533@shbuild999.sh.intel.com> <20200705125854.GA66252@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200705125854.GA66252@shbuild999.sh.intel.com> 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 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. 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? 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 > >