On 12/3/25 07:12, Shakeel Butt wrote:
> On Mon, Nov 24, 2025 at 08:38:15PM +0800, Guopeng Zhang wrote:
>> test_memcg_sock() currently requires that memory.stat's "sock " counter
>> is exactly zero immediately after the TCP server exits. On a busy system
>> this assumption is too strict:
>>
>> - Socket memory may be freed with a small delay (e.g. RCU callbacks).
>> - memcg statistics are updated asynchronously via the rstat flushing
>> worker, so the "sock " value in memory.stat can stay non-zero for a
>> short period of time even after all socket memory has been uncharged.
>>
>> As a result, test_memcg_sock() can intermittently fail even though socket
>> memory accounting is working correctly.
>>
>> Make the test more robust by polling memory.stat for the "sock "
>> counter and allowing it some time to drop to zero instead of checking
>> it only once. The timeout is set to 3 seconds to cover the periodic
>> rstat flush interval (FLUSH_TIME = 2*HZ by default) plus some
>> scheduling slack. If the counter does not become zero within the
>> timeout, the test still fails as before.
>>
>> On my test system, running test_memcontrol 50 times produced:
>>
>> - Before this patch: 6/50 runs passed.
>> - After this patch: 50/50 runs passed.
>>
>> Signed-off-by: Guopeng Zhang <[email protected]>
>> Suggested-by: Lance Yang <[email protected]>
>> ---
>> .../selftests/cgroup/test_memcontrol.c | 20 ++++++++++++++++++-
>> 1 file changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c
>> b/tools/testing/selftests/cgroup/test_memcontrol.c
>> index 4e1647568c5b..dda12e5c6457 100644
>> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
>> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
>> @@ -21,6 +21,8 @@
>> #include "kselftest.h"
>> #include "cgroup_util.h"
>>
>> +#define MEMCG_SOCKSTAT_WAIT_RETRIES 30 /* 3s total */
>
> No need for the comment at the end as it will be stale when someone
> change DEFAULT_WAIT_INTERVAL_US in future.
>
> Anyways it's a nit.
>
> Reviewed-by: Shakeel Butt <[email protected]>
Hi Shakeel,
Thanks for the review and for the Reviewed-by.
Good point about the comment. I’ll drop the "/* 3s total */" part in the next
version so it does not become stale if DEFAULT_WAIT_INTERVAL_US changes.
Thanks,
Guopeng
