tree e016935db70c30773654897dd2a85f597f3915e0
parent e0d8534b7ac36e950c35c6ec6c576f94d5a25433
author Cyril Hrubis <chrubis@suse.cz> 1489403196 +0100
committer Cyril Hrubis <chrubis@suse.cz> 1490102861 +0100

madvise09: Add MADV_FREE test

We test the madvise(MADV_FREE) by running a process in a memory cgroup
with fairly small memory limits. The test process forks a child, moves
it to the newly created cgroup. The child allocates memory, marks it
MADV_FREE then forks a memory hungry child that allocates and faults
memory in a loop. Due to undeterministic nature of the OOM (that kills
the memory hungry child sooner or later) we have to retry at two levels.
First problem is that rarely it gets too rogue and both processes in the
cgroup gets killed. The second is that sometimes the memory hungry child
is killed too fast (before the kernel has chance to free the pages), so
we rerun it a (for a few times) if that happens.

The test expects memory cgroup mounted in the standard /sys/fs/cgroup/
path, which is OK since the functionality tested was added to kernel
4.5 and the test would be skipped on older distros anyway.

Also the test expects that the MADV_FREE pages will not be freed
immediatelly hence the test will fail if the whole system is under
memory pressure.

The memory limits were choosen to be 8MB and 16MB for memsw limit. I've
tried to use to base these on usage_in_bytes but that turned out to be
source of random errors. It worked fine and produces stable numbers 99%
of the time but then the numbers have changed and caused the test to
fail in fork() with ENOMEM.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Acked-by: Jan Stancek <jstancek@redhat.com>