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[70.44.39.90]) by smtp.gmail.com with ESMTPSA id 2sm9864869qkf.97.2021.02.05.09.50.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Feb 2021 09:50:14 -0800 (PST) Date: Fri, 5 Feb 2021 12:50:13 -0500 From: Johannes Weiner To: Roman Gushchin Cc: Andrew Morton , Tejun Heo , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 1/7] mm: memcontrol: fix cpuhotplug statistics flushing Message-ID: References: <20210202184746.119084-1-hannes@cmpxchg.org> <20210202184746.119084-2-hannes@cmpxchg.org> <20210202230747.GA1812008@carbon.dhcp.thefacebook.com> <20210203022853.GG1812008@carbon.dhcp.thefacebook.com> <20210204193446.GA2053875@carbon.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210204193446.GA2053875@carbon.dhcp.thefacebook.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 04, 2021 at 11:34:46AM -0800, Roman Gushchin wrote: > On Thu, Feb 04, 2021 at 02:29:57PM -0500, Johannes Weiner wrote: > > It even passes with a reduced margin in the patched kernel, since the > > percpu drift - which this test already tried to account for - is now > > only on the page_counter side (whereas memory.stat is always precise). > > > > I'm going to include that data in the v2 changelog, as well as a patch > > to update test_kmem.c to the more stringent error tolerances. > > Hm, I'm not sure it's a good idea to unconditionally lower the error tolerance: > it's convenient to be able to run the same test on older kernels. Well, an older version of the kernel will have an older version of the test that is tailored towards that kernel's specific behavior. That's sort of the point of tracking code and tests in the same git tree: to have meaningful, effective and precise tests of an ever-changing implementation. Trying to be backward compatible will lower the test signal and miss regressions, when a backward compatible version is at most one git checkout away.