linux-kernel - Re: [PATCH -next RFC 05/16] cpuset: factor out partition

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Message-ID: <6122ac29-3984-4364-ab37-4987b65b5450@redhat.com>
Date: Sun, 19 Oct 2025 22:43:12 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, tj@...nel.org,
 hannes@...xchg.org, mkoutny@...e.com
Cc: cgups@...r.kernel.org, linux-kernel@...r.kernel.org,
 lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next RFC 05/16] cpuset: factor out partition_update()
 function

On 9/28/25 3:12 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
>
> Extract the core partition update logic into a dedicated partition_update()
> function. This refactoring centralizes updates to key cpuset data
> structures including remote_sibling, effective_xcpus, partition_root_state,
> and prs_err.
>
> The function handles the complete partition update workflow:
> - Adding and removing exclusive CPUs via partition_xcpus_add()/del()
> - Managing remote sibling relationships
> - Synchronizing effective exclusive CPUs mask
> - Updating partition state and error status
> - Triggering required system updates and workqueue synchronization
>
> This creates a coherent interface for partition operations and establishes
> a foundation for enhanced partition management while maintaining existing
> remote partition behavior.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
>   kernel/cgroup/cpuset.c | 71 ++++++++++++++++++++++++++++--------------
>   1 file changed, 47 insertions(+), 24 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 1944410ae872..0e2f95daf459 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1587,6 +1587,49 @@ static void partition_disable(struct cpuset *cs, struct cpuset *parent,
>   	cpuset_force_rebuild();
>   }
>   
> +/**
> + * partition_update - Update an existing partition configuration
> + * @cs: The cpuset to update
> + * @prs: Partition root state (must be positive)
> + * @xcpus: New exclusive CPUs mask for the partition (NULL to keep current)
> + * @excpus: New effective exclusive CPUs mask
> + * @tmp: Temporary masks
> + *
> + * Updates partition-related fields. The tmp->addmask is the CPU mask that
> + * will be added to the subpartitions_cpus and removed from parent's
> + * effective_cpus, and the tmp->delmask vice versa.
> + */
> +static void partition_update(struct cpuset *cs, int prs, struct cpumask *xcpus,
> +				  struct cpumask *excpus, struct tmpmasks *tmp)
> +{
> +	bool isolcpus_updated;
> +	bool excl_updated;
> +	struct cpuset *parent;
> +
> +	lockdep_assert_held(&cpuset_mutex);
> +	WARN_ON_ONCE(!cpuset_v2());
> +	WARN_ON_ONCE(prs <= 0);
> +
> +	parent = is_remote_partition(cs) ? NULL : parent_cs(cs);
> +	excl_updated = !cpumask_empty(tmp->addmask) ||
> +			!cpumask_empty(tmp->delmask);
> +
> +	spin_lock_irq(&callback_lock);
> +	isolcpus_updated = partition_xcpus_add(prs, parent, tmp->addmask);
> +	isolcpus_updated |= partition_xcpus_del(prs, parent, tmp->delmask);

The current partition_xcpus_add/del() functions assume the given cpumas 
is non-empty. In the new partition_update() helper, you can pass an 
empty cpumask to them. This will cause useless work to be done. Also 
isolcpus_update may not be correct because of that causing unneeded work 
to be done in the workqueue code.

-Longman