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Fri, 11 Apr 2025 10:22:50 -0700 (PDT) Received: from blackdock.suse.cz ([193.86.92.181]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43f20626c0csm96273275e9.14.2025.04.11.10.22.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Apr 2025 10:22:49 -0700 (PDT) Date: Fri, 11 Apr 2025 19:22:48 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Waiman Long Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Tejun Heo , Shuah Khan , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v5 2/2] selftests: memcg: Increase error tolerance of child memory.current check in test_memcg_protection() Message-ID: References: <20250407162316.1434714-1-longman@redhat.com> <20250407162316.1434714-3-longman@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="flingjnfq7xpj56j" Content-Disposition: inline In-Reply-To: <20250407162316.1434714-3-longman@redhat.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BFFB4140008 X-Stat-Signature: wbczth5j4ztq9tatu65foogbrnnb1gmu X-Rspam-User: X-HE-Tag: 1744392171-162785 X-HE-Meta: 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 e0eRACdS 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --flingjnfq7xpj56j Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v5 2/2] selftests: memcg: Increase error tolerance of child memory.current check in test_memcg_protection() MIME-Version: 1.0 On Mon, Apr 07, 2025 at 12:23:16PM -0400, Waiman Long = wrote: > Child Actual usage Expected usage %err > ----- ------------ -------------- ---- > 1 16990208 22020096 -12.9% > 1 17252352 22020096 -12.1% > 0 37699584 30408704 +10.7% > 1 14368768 22020096 -21.0% > 1 16871424 22020096 -13.2% >=20 > The current 10% error tolerenace might be right at the time > test_memcontrol.c was first introduced in v4.18 kernel, but memory > reclaim have certainly evolved quite a bit since then which may result > in a bit more run-to-run variation than previously expected. I like Roman's suggestion of nr_cpus dependence but I assume your variations were still on the same system, weren't they? Is it fair to say that reclaim is chaotic [1]? I wonder what may cause variations between separate runs of the test. Would it help to `echo 3 >drop_caches` before each run to have more stable initial conditions? (Not sure if it's OK in selftests.) Or sleep 0.5s to settle rstat flushing? No, page_counter's don't suffer that but stock MEMCG_CHARGE_BATCH in percpu stocks. So maybe drain the stock so that counters are precise after the test? (Either by executing a dummy memcg on each CPU or via some debugging API.) Michal [1] https://en.wikipedia.org/wiki/Chaos_theory#Chaotic_dynamics --flingjnfq7xpj56j Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTd6mfF2PbEZnpdoAkt3Wney77BSQUCZ/lP5gAKCRAt3Wney77B STuPAP9qtXHRJuw6fswvLPcE6FAyBPPV35k6ECqWkmzYm2zgJgD/Q60WvtRy+kc1 RSJih7a7z5QbobgKcZhdynqI/a5/iQI= =SyIA -----END PGP SIGNATURE----- --flingjnfq7xpj56j--