linux-kernel - Re: [PATCH v3] cgroup/cpuset: fmeter_getrate() returns 0 when memory

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Message-ID: <3722eb57-1108-46e5-908b-66dd7ac0126b@redhat.com>
Date: Mon, 17 Feb 2025 16:28:53 -0500
From: Waiman Long <llong@...hat.com>
To: Jin Guojie <guojie.jin@...il.com>, cgroups@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Michal Koutný <mkoutny@...e.com>
Subject: Re: [PATCH v3] cgroup/cpuset: fmeter_getrate() returns 0 when
 memory_pressure disabled

On 2/17/25 2:15 AM, Jin Guojie wrote:
> When running LTP's cpuset_memory_pressure program, an error can be
> reproduced by the following steps:
>
> (1) Create a cgroup, enable cpuset subsystem, set memory limit, and
> then set cpuset_memory_pressure to 1
> (2) In this cgroup, create a process to allocate a large amount of
> memory and generate pressure counts
> (3) Set cpuset_memory_pressure to 0
> (4) Check cpuset.memory_pressure: LTP thinks it should be 0, but the
> kernel returns a value of 1, so LTP determines it as FAIL
>
> In the current kernel, the variable cpuset_memory_pressure_enabled is
> not actually used。

That statement is not true. cpuset_memory_pressure_enabled is used to 
determine if __cpuset_memory_pressure_bump() should be called in 
cpuset_memory_pressure_bump().

>
> This patch modifies fmeter_getrate() to determine whether to return 0
> based on cpuset_memory_pressure_enabled.
>
> Signed-off-by: Jin Guojie <guojie.jin@...il.com>
> Suggested-by: Michal Koutný <mkoutny@...e.com>

What Michal suggested is the approach you used in v2, but it has problem 
as I mentioned previously.

Other than that,

Acked-by: Waiman Long <longman@...hat.com>

> Suggested-by: Waiman Long <longman@...hat.com>
> ---
>   kernel/cgroup/cpuset-v1.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
> index 25c1d7b77e2f..14564e91e2b3 100644
> --- a/kernel/cgroup/cpuset-v1.c
> +++ b/kernel/cgroup/cpuset-v1.c
> @@ -108,7 +108,7 @@ static int fmeter_getrate(struct fmeter *fmp)
>   	fmeter_update(fmp);
>   	val = fmp->val;
>   	spin_unlock(&fmp->lock);
> -	return val;
> +	return cpuset_memory_pressure_enabled ? val : 0;
>   }
>   
>   /*