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

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Message-ID: <8ce13061-b4a7-4474-9e57-bab9b1a62b63@linux.dev>
Date: Thu, 27 Nov 2025 18:55:37 +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 2025/11/24 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 ...