linux-kernel - Re: [PATCH v4 1/1] cpuset: relax the overlap check for cgroup-v2

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Message-Id: <20251119110546.1387184-1-sunshaojie@kylinos.cn>
Date: Wed, 19 Nov 2025 19:05:46 +0800
From: Sun Shaojie <sunshaojie@...inos.cn>
To: llong@...hat.com
Cc: cgroups@...r.kernel.org,
	chenridong@...weicloud.com,
	hannes@...xchg.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	mkoutny@...e.com,
	shuah@...nel.org,
	sunshaojie@...inos.cn,
	tj@...nel.org
Subject: Re: [PATCH v4 1/1] cpuset: relax the overlap check for cgroup-v2

Hi, Longman,

On Tue, 18 Nov 2025 14:53:27 -0500, Longman wrote:
>On 11/16/25 8:57 PM, Sun Shaojie wrote:
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 52468d2c178a..0fd803612513 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -580,35 +580,56 @@ static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
>>   
>>   /**
>>    * cpus_excl_conflict - Check if two cpusets have exclusive CPU conflicts
>> - * @cs1: first cpuset to check
>> - * @cs2: second cpuset to check
>> + * @cs1: current cpuset to check
>> + * @cs2: cpuset involved in the check
>>    *
>>    * Returns: true if CPU exclusivity conflict exists, false otherwise
>>    *
>>    * Conflict detection rules:
>> - * 1. If either cpuset is CPU exclusive, they must be mutually exclusive
>> + * For cgroup-v1:
>> + *     see cpuset1_cpus_excl_conflict()
>> + * For cgroup-v2:
>> + * 1. If cs1 is exclusive, cs1 and cs2 must be mutually exclusive
>>    * 2. exclusive_cpus masks cannot intersect between cpusets
>> - * 3. The allowed CPUs of one cpuset cannot be a subset of another's exclusive CPUs
>> + * 3. If cs2 is exclusive, cs2's allowed CPUs cannot be a subset of cs1's exclusive CPUs
>> + * 4. if cs1 and cs2 are not exclusive, the allowed CPUs of one cpuset cannot be a subset
>> + *    of another's exclusive CPUs
>>    */
>>   static inline bool cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
>
>As cs1 and cs2 is going to be handled differently, their current naming 
>will make it hard to understand why they are treated differently. I will 
>recommended changing the parameter name to "trial, sibling" as the 
>caller call it with "cpus_excl_conflict(trial, c)" where trial is the 
>new cpuset data to be tested and sibling is one of its sibling cpusets. 
>It has to be clearly document what each parameter is for and the fact 
>that swapping the parameters will cause it to return incorrect result.
>
>
>>   {
>> -	/* If either cpuset is exclusive, check if they are mutually exclusive */
>> -	if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
>> +	/* For cgroup-v1 */
>> +	if (!cpuset_v2())
>> +		return cpuset1_cpus_excl_conflict(cs1, cs2);
>> +
>> +	/* If cs1 are exclusive, check if they are mutually exclusive */
>> +	if (is_cpu_exclusive(cs1))
>>   		return !cpusets_are_exclusive(cs1, cs2);
>
>Code change like the following can eliminate the need to introduce a new 
>cpuset1_cpus_excl_conflict() helper.
>
>diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>index ec8bebc66469..201c70fb7401 100644
>--- a/kernel/cgroup/cpuset.c
>+++ b/kernel/cgroup/cpuset.c
>@@ -599,9 +599,15 @@ static inline bool cpusets_are_exclusive(struct 
>cpuset *cs1, struct cpuset *cs2)
>   */
>  static inline bool cpus_excl_conflict(struct cpuset *cs1, struct 
>cpuset *cs2)
>  {
>-       /* If either cpuset is exclusive, check if they are mutually 
>exclusive */
>-       if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
>-               return !cpusets_are_exclusive(cs1, cs2);
>+       /*
>+        * If trial is exclusive or sibling is exclusive & in v1,
>+        * check if they are mutually exclusive
>+        */
>+       if (is_cpu_exclusive(trial) || (!cpuset_v2() && 
>is_cpu_exclusive(sibling)))
>+               return !cpusets_are_exclusive(trial, sibling);
>+
>+       if (!cpuset_v2())
>+               return false;   /* The checking below is irrelevant to 
>cpuset v1 */
>
>         /* Exclusive_cpus cannot intersect */
>         if (cpumask_intersects(cs1->exclusive_cpus, cs2->exclusive_cpus))

Thank you very much for your guidance and suggestions on the code.

I've updated patch v5 with some new ideas and look forward to your feedback.

patch v5 : https://lore.kernel.org/cgroups/20251119105749.1385946-1-sunshaojie@kylinos.cn/

Thanks,
Sun Shaojie