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McKenney" Cc: Johannes Weiner , 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: References: <20230801135632.1768830-1-hannes@cmpxchg.org> MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20230517 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B3E8C1C0017 X-Stat-Signature: 39e74j9igsnxjfbfkm5mx6gpew1po7pq X-Rspam-User: X-HE-Tag: 1691079218-608312 X-HE-Meta: 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 08MhNQdm 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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 09:39:28AM -0700, Paul E. McKenney wrote: > 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 > > The same issue exists in the test case test_kmem_memcg_deletion. I wouldn't mind posting the patch, but it seems you want to propose something more formal. Let me know your opinion. Thanks, Lucas