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McKenney" To: Johannes Weiner Cc: Andrew Morton , Roman Gushchin , Michal Hocko , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] selftests: cgroup: fix test_kmem_basic false positives Message-ID: Reply-To: paulmck@kernel.org References: <20230801135632.1768830-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230801135632.1768830-1-hannes@cmpxchg.org> X-Rspamd-Queue-Id: BF38A12137A X-Rspam-User: X-Stat-Signature: 66u775qpds39d8x7w5o9eme8x6nwjxcr X-Rspamd-Server: rspam03 X-HE-Tag: 1690907970-760005 X-HE-Meta: U2FsdGVkX19l1gY7eWS6PNyCHqz/81JwCkgPSttCu6na+xgJNX2IjBF1Ics2JcyXCP6pFgd8j6/ma1lZlni3pvmK4evQ6pEpt7VbFZtlmohMv0YvlEjWDIz4HVa/dnKIiVfpKsCcMeuNckLl3xeXh4VBE5IWcxfdMcCxZX3qayFZ/ZY7laekSoKqtgFF43jzoVcQujBPgYCowt/B+6XEY60KAjSMxGEFM3DioPtxuT3gIDSn1QbQel+D9vj2GL0FbUatO0UK7XKu7qW6Y54JFvajux+Xx2Rtv7s6oEtkoyOLC0+zNUc5WxroiLHOpZII/0vKiM0sRmCeE6dByoYg7RvDqITx3b2H64XcdAfHCg1kE4um3zFluoDJQLGjbTt/SsMX7sjsuOUhnGHIz9ya5rnHdKByYyeWK7NGcXDMXErDGaXBv3jbqzlIlN8DnrgNIPNx7E/Xy+kUAa1xCMy14a93mpyoI9KDpeLV2EJYdA5HhpGUrRoliEbH159pZ1oXNDr+fAwy71p8cepk3zRNdX1NnvhPLRYifACHFlXlOJwvXxA7Va/UtCXzXTeDq1V8v043lqj4Lb2lPdnESUGa4In0Wx1t7KpkCPYDBaqS3CejGDkMurpnYYcxqOcV34lHBqVr3sR8BivGfnkwoqskfP/Ykxgqq82mH8HY3bXm5p5nlhanWvJmYCmvyYLb2GcOuQXOoaJSvKQeMMoc+QHW1Z4d+RO62Acid8Kq0jU1J5abD7EflDbQaUSvRVUjg6bjPCHDqxHGtCQGXZB8eFM6IFAsbghR8FUraIMbLjVxjrm7RlZKegU7oy6Zp522dLRC0BPUs0Ib5lE9pjjD4RZbfA36OcwR15U293LVHfAQWQ7rL98rwS/CVH5hmmNnBcwAMB/25usCzG0RX+M5QF51IRzr3Xcj1glxMNNRBmRkBxUN1PVAhbyszGnMcdfg7PAdWEsk45ssN6zqQeUkEHM ws9TKp5S 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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 Tue, Aug 01, 2023 at 09:56:32AM -0400, Johannes Weiner wrote: > This test fails routinely in our prod testing environment, and I can > reproduce it locally as well. > > The test allocates dcache inside a cgroup, then drops the memory limit > and checks that usage drops correspondingly. 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 dropping the limit. This should be good > enough, assuming that machines running those tests are otherwise not > very busy. > > Signed-off-by: Johannes Weiner I am putting together something more formal, but this will certainly improve things, as Johannes says, assuming the system goes mostly idle during that one-second wait. So: Acked-by: Paul E. McKenney Yes, there are corner cases, such as the system having millions of RCU callbacks queued and being unable to invoke them all during that one-second interval. But that is a corner case, and that is exactly why I will be putting together something more formal. ;-) Thanx, Paul > --- > tools/testing/selftests/cgroup/test_kmem.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c > index 258ddc565deb..1b2cec9d18a4 100644 > --- a/tools/testing/selftests/cgroup/test_kmem.c > +++ b/tools/testing/selftests/cgroup/test_kmem.c > @@ -70,6 +70,10 @@ static int test_kmem_basic(const char *root) > goto cleanup; > > cg_write(cg, "memory.high", "1M"); > + > + /* wait for RCU freeing */ > + sleep(1); > + > slab1 = cg_read_key_long(cg, "memory.stat", "slab "); > if (slab1 <= 0) > goto cleanup; > -- > 2.41.0 >