linux-kernel - Re: [PATCH v5 2/3] selftests: cgroup: make test_memcg

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Message-ID: <dyie6co47aemejhok5xjjmsvfjpsg2djmkbucnonent3afqylm@ojui2r4gb3ro>
Date: Thu, 4 Dec 2025 16:04:35 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Guopeng Zhang <zhangguopeng@...inos.cn>
Cc: tj@...nel.org, hannes@...xchg.org, shuah@...nel.org, 
	roman.gushchin@...ux.dev, lance.yang@...ux.dev, shakeel.butt@...ux.dev, 
	muchun.song@...ux.dev, linux-kselftest@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] selftests: cgroup: make test_memcg_sock robust
 against delayed sock stats

On Wed, Dec 03, 2025 at 07:56:30PM +0800, Guopeng Zhang <zhangguopeng@...inos.cn> 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>
> Reviewed-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
>  .../selftests/cgroup/test_memcontrol.c        | 20 ++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)

Acked-by: Michal Koutný <mkoutny@...e.com>

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