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Fri, 04 Aug 2023 09:37:18 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:9910]) by smtp.gmail.com with ESMTPSA id e29-20020a0cb45d000000b00632266b569esm782221qvf.87.2023.08.04.09.37.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Aug 2023 09:37:17 -0700 (PDT) Date: Fri, 4 Aug 2023 12:37:16 -0400 From: Johannes Weiner To: Lucas Karpinski Cc: Andrew Morton , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Tejun Heo , Zefan Li , Shuah Khan , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] selftests: cgroup: fix test_kmem_memcg_deletion false positives Message-ID: <20230804163716.GA337691@cmpxchg.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 4F86F40009 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: qbcqfdw6opqm8ocoznafq43h653joi9t X-HE-Tag: 1691167039-809602 X-HE-Meta: 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 J7qUVP2o 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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: On Fri, Aug 04, 2023 at 11:37:33AM -0400, Lucas Karpinski wrote: > The test allocates dcache inside a cgroup, then destroys the cgroups and > then checks the sanity of numbers on the parent level. The reason it > fails is because dentries are freed with an RCU delay - a debugging > sleep shows that usage drops as expected shortly after. > > Insert a 1s sleep after completing the cgroup creation/deletions. This > should be good enough, assuming that machines running those tests are > otherwise not very busy. This commit is directly inspired by Johannes > over at the link below. > > Link: https://lore.kernel.org/all/20230801135632.1768830-1-hannes@cmpxchg.org/ > > Signed-off-by: Lucas Karpinski Maybe I'm missing something, but there isn't a limit set anywhere that would cause the dentries to be reclaimed and freed, no? When the subgroups are deleted, the objects are just moved to the parent. The counters inside the parent (which are hierarchical) shouldn't change. So this seems to be a different scenario than test_kmem_basic. If the test is failing for you, I can't quite see why.