Re: [RFC PATCH -v4 04/22] cpuset: introduce partition_enable()

[Ridong Chen <ridong.chen@linux.dev>]

On 11/3/2026 6:26 PM, Guopeng Zhang wrote:
> 
> 在 2026/11/1 19:41, Ridong Chen 写道:
>> From: Chen Ridong<chenridong@huawei.com>
>>
>> Add partition_enable() to consolidate updates to key cpuset structures
>> during partition enablement, including:
>> 1. remote_partition
>> 2. effective_xcpus
>> 3. partition_root_state
>> 4. prs_err
>>
>> Key operations performed:
>> 1. Invokes partition_xcpus_add() to assign exclusive CPUs
>> 2. Maintains remote partition flag
>> 3. Syncs the effective_xcpus mask
>> 4. Updates partition_root_state and prs_err
>> 5. Triggers scheduler domain rebuilds
>> 6. Sends partition change notifications
>>
>> This helper also handles the transition between root and isolated
>> states of a valid partition. In that case the cpumasks are unchanged
>> and only isolated_cpus is updated.
>>
>> A partition_state_update() helper is added to set partition_root_state
>> and prs_err, and to reset the partition data when the new state is not
>> a valid partition.
>>
>> Signed-off-by: Chen Ridong<chenridong@huawei.com>
>> Signed-off-by: Ridong Chen<chenridong@xiaomi.com>
>> ---
>>   kernel/cgroup/cpuset.c | 51 ++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 51 insertions(+)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index df52f6e5e99f..052a131731dd 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -1716,6 +1716,57 @@ static void compute_effective_nodemask(nodemask_t *new_mems,
>>   		nodes_copy(*new_mems, parent->effective_mems);
>>   }
>>   
>> +static void partition_state_update(struct cpuset *cs, int new_prs,
>> +				   enum prs_errcode prs_err)
>> +{
>> +	lockdep_assert_held(&callback_lock);
>> +
>> +	cs->partition_root_state = new_prs;
>> +	WRITE_ONCE(cs->prs_err, prs_err);
>> +	if (!is_partition_valid(cs))
>> +		reset_partition_data(cs);
>> +}
>> +
>> +/**
>> + * partition_enable - Transitions a cpuset to a partition root
>> + * @cs: The cpuset to enable partition for
>> + * @parent: Parent cpuset of @cs, NULL for remote parent
>> + * @new_prs: New partition state to set
>> + * @new_excpus: New effective exclusive CPUs mask for the partition
>> + *
>> + * Transitions a cpuset to a partition root, only for v2.
>> + * It also supports the transition between root and isolated partition.
>> + */
>> +static void partition_enable(struct cpuset *cs, struct cpuset *parent,
>> +			     int new_prs, struct cpumask *new_excpus)
> Should we consider the bisection case here? With CONFIG_WERROR=y this
> patch fails to build on its own — partition_enable() is defined but not
> used.
> 

Hi Guopeng,

Thanks for catching this. You are right, each patch should build on
its own, and with CONFIG_WERROR=y these helpers trigger
-Wunused-function until they are used in patches 7-9.

The helpers are introduced in separate patches on purpose: Waiman
suggested having them complete when introduced, and then converting
remote and local partitions to them in later patches, to make the
series easier to review [1]. To keep that and still build cleanly,
I'll mark them __maybe_unused when they are introduced, and drop it
in the patch that first uses each of them.

[1] https://lore.kernel.org/all/e8018984-96ed-49fa-8571-79a0d39cb218@redhat.com/

> 
>> +{
>> +	int old_prs = cs->partition_root_state;
>> +
>> +	lockdep_assert_cpuset_lock_held();
>> +	WARN_ON_ONCE(new_prs <= 0);
>> +	WARN_ON_ONCE(!cpuset_v2());
>> +
>> +	if (old_prs == new_prs)
>> +		return;
>> +
>> +	spin_lock_irq(&callback_lock);
>> +	if (old_prs > 0) {
>> +		/* Switch between root and isolated, cpumasks are unchanged */
>> +		isolated_cpus_update(old_prs, new_prs, cs->effective_xcpus);
>> +	} else {
>> +		/* enable partition should only add exclusive cpus */
>> +		partition_xcpus_add(new_prs, parent, new_excpus);
>> +		/* enable remote partition */
>> +		if (!parent)
>> +			cs->remote_partition = true;
>> +		cpumask_copy(cs->effective_xcpus, new_excpus);
>> +	}
>> +	partition_state_update(cs, new_prs, PERR_NONE);
>> +	spin_unlock_irq(&callback_lock);
>> +	cpuset_force_rebuild();
>> +	notify_partition_change(cs, old_prs);
>> +}
>> +
>>   /*
>>    * remote_partition_enable - Enable current cpuset as a remote partition root
>>    * @cs: the cpuset to update
> 

-- 
Best regards
Ridong