linux-kernel - Re: [PATCH v4 2/3] selftests: cgroup: make test_memcg

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Message-ID: <4056b77f-ea23-4c49-975c-006a4a8b4733@linux.dev>
Date: Thu, 27 Nov 2025 19:29:58 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: Guopeng Zhang <zhangguopeng@...inos.cn>
Cc: shuah@...nel.org, muchun.song@...ux.dev, mkoutny@...e.com,
 linux-mm@...ck.org, linux-kselftest@...r.kernel.org, shakeel.butt@...ux.dev,
 linux-kernel@...r.kernel.org, tj@...nel.org, hannes@...xchg.org,
 mhocko@...nel.org, roman.gushchin@...ux.dev,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 2/3] selftests: cgroup: make test_memcg_sock robust
 against delayed sock stats



On 2025/11/27 19:18, Guopeng Zhang wrote:
> 
> 
> On 11/27/25 18:55, Lance Yang wrote:
>>
>>
>> On 2025/11/24 20:38, 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 <zhangguopeng@...inos.cn>
>>> Suggested-by: Lance Yang <lance.yang@...ux.dev>
>>> ---
>>>    .../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"
>>
>> This patch fails to apply to mm-new ...
>>
>> Hmm, it expects #include "kselftest.h" here, but the tree uses
>> #include "../kselftest.h".
>>
>> Which is odd, as that line hasn't been touched in years ...
> Hi,lance
> 
> Thanks for your review.
> 
> When I prepared this patch I was working on linux-next, where
> tools/testing/selftests/cgroup/test_memcontrol.c already uses:
> 
>      #include "kselftest.h"
> 
> I just checked, and this change comes from the following commit:
> 
>      1aaedc385b9b278dcf91f4e9d0c3e1a078804ff1
>      https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20251127&id=1aaedc385b9b278dcf91f4e9d0c3e1a078804ff1
> 
> So the patch applies cleanly on top of the latest linux-next, but not on
> mm-new which still has `#include "../kselftest.h"`.

Ahh, I see, thanks!