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

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Message-ID: <07b9bdd1-3499-41a7-bef2-9428935fd3f1@kylinos.cn>
Date: Thu, 27 Nov 2025 19:18:15 +0800
From: Guopeng Zhang <zhangguopeng@...inos.cn>
To: Lance Yang <lance.yang@...ux.dev>
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 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"`.

Thanks,
Guopeng