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 <hannes@xxxxxxxxxxx> 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 <paulmck@xxxxxxxxxx> 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 >
