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[37.188.179.51]) by smtp.gmail.com with ESMTPSA id u15sm1211094wrm.64.2020.07.07.06.56.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2020 06:56:45 -0700 (PDT) Date: Tue, 7 Jul 2020 15:56:43 +0200 From: Michal Hocko To: Qian Cai Cc: Feng Tang , kernel test robot , Andrew Morton , 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: <20200707135643.GV5913@dhcp22.suse.cz> References: <20200707120619.GO5913@dhcp22.suse.cz> <20200707130436.GA992@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200707130436.GA992@lca.pw> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 07-07-20 09:04:36, Qian Cai wrote: > On Tue, Jul 07, 2020 at 02:06:19PM +0200, Michal Hocko wrote: > > On Tue 07-07-20 07:43:48, Qian Cai wrote: > > > > > > > > > > On Jul 7, 2020, at 6:28 AM, Michal Hocko wrote: > > > > > > > > Would you have any examples? Because I find this highly unlikely. > > > > OVERCOMMIT_NEVER only works when virtual memory is not largerly > > > > overcommited wrt to real memory demand. And that tends to be more of > > > > an exception rather than a rule. "Modern" userspace (whatever that > > > > means) tends to be really hungry with virtual memory which is only used > > > > very sparsely. > > > > > > > > I would argue that either somebody is running an "OVERCOMMIT_NEVER" > > > > friendly SW and this is a permanent setting or this is not used at all. > > > > At least this is my experience. > > > > > > > > So I strongly suspect that LTP test failure is not something we should > > > > really lose sleep over. It would be nice to find a way to flush existing > > > > batches but I would rather see a real workload that would suffer from > > > > this imprecision. > > > > > > I hear you many times that you really don’t care about those use > > > cases unless you hear exactly people are using in your world. > > > > > > For example, when you said LTP oom tests are totally artificial last > > > time and how less you care about if they are failing, and I could only > > > enjoy their efficiencies to find many issues like race conditions > > > and bad error accumulation handling etc that your “real world use > > > cases” are going to take ages or no way to flag them. > > > > Yes, they are effective at hitting corner cases and that is fine. I > > am not dismissing their usefulness. I have tried to explain that many > > times but let me try again. Seeing a corner case and think about a > > potential fix is one thing. On the other hand it is not really ideal to > > treat such a failure a hard regression and consider otherwise useful > > Well, terms like "corner cases" and "hard regression" are rather > subjective. Existing real life examples really makes them less subjective though. [...] > > LTP is a very useful tool to raise awareness of potential problems but > > you shouldn't really follow those results just blindly. > > You must think I am a newbie tester to give me this piece of advice > then. Not by even close. I can clearly see your involvement in testing and how many good bug reports that results in. -- Michal Hocko SUSE Labs