On 11/20/25 13:40, Lance Yang wrote:
>
>
> On 2025/11/20 11:16, 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.
>>
>> Suggested-by: Lance Yang <[email protected]>
>> Signed-off-by: Guopeng Zhang <[email protected]>
>> ---
>> v2:
>> - Mention the periodic rstat flush interval (FLUSH_TIME = 2*HZ) in
>> the comment and clarify the rationale for the 3s timeout.
>> - Replace the hard-coded retry count and wait interval with macros
>> to avoid magic numbers and make the 3s timeout calculation explicit.
>> ---
>> .../selftests/cgroup/test_memcontrol.c | 30 ++++++++++++++++++-
>> 1 file changed, 29 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c
>> b/tools/testing/selftests/cgroup/test_memcontrol.c
>> index 4e1647568c5b..7bea656658a2 100644
>> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
>> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
>> @@ -24,6 +24,9 @@
>> static bool has_localevents;
>> static bool has_recursiveprot;
>> +#define MEMCG_SOCKSTAT_WAIT_RETRIES 30 /* 3s total */
>> +#define MEMCG_SOCKSTAT_WAIT_INTERVAL_US (100 * 1000) /* 100 ms */
>
> Nit: Defines are usually placed at the top of the file (e.g., after the
> #include block). Placing them between global variables and functions
> looks a bit out of place, IMHO ...
> Otherwise, feel free to add:
>
> Reviewed-by: Lance Yang <[email protected]>
> [...]
>
> Cheers,
> Lance
Thanks for the review and the suggestion!
Good point about the placement of the defines — I’ll move
MEMCG_SOCKSTAT_WAIT_* after the #include block in v3 as you suggested,
and I’ll add your:
Reviewed-by: Lance Yang <[email protected]>
as well.
Thanks again!
Best regards,
Guopeng
