Re: [PATCH -next v2 2/3] cpuset: remove global remote_children list

[Waiman Long <llong@redhat.com>]

On 11/11/25 8:24 AM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
>
> The remote_children list is used to track all remote partitions attached
> to a cpuset. However, it serves no other purpose. Using a boolean flag to
> indicate whether a cpuset is a remote partition is a more direct approach,
> making remote_children unnecessary.
>
> This patch replaces the list with a remote_partition flag in the cpuset
> structure and removes remote_children entirely.
>
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   kernel/cgroup/cpuset-internal.h | 10 +++++++---
>   kernel/cgroup/cpuset.c          | 13 ++++---------
>   2 files changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index 5cac42c5fd97..01976c8e7d49 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -158,6 +158,13 @@ struct cpuset {
>   	/* partition root state */
>   	int partition_root_state;
>   
> +	/*
> +	 * Whether cpuset is a remote partition.
> +	 * It used to be a list anchoring all remote partitions — we can switch back
> +	 * to a list if we need to iterate over the remote partitions.
> +	 */
> +	bool remote_partition;
> +
>   	/*
>   	 * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
>   	 * know when to rebuild associated root domain bandwidth information.
> @@ -172,9 +179,6 @@ struct cpuset {
>   	/* Handle for cpuset.cpus.partition */
>   	struct cgroup_file partition_file;
>   
> -	/* Remote partition silbling list anchored at remote_children */
> -	struct list_head remote_sibling;
> -
>   	/* Used to merge intersecting subsets for generate_sched_domains */
>   	struct uf_node node;
>   };
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index c90476d52f09..aff3ddc67393 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -94,9 +94,6 @@ static bool isolated_cpus_updating;
>   static cpumask_var_t	boot_hk_cpus;
>   static bool		have_boot_isolcpus;
>   
> -/* List of remote partition root children */
> -static struct list_head remote_children;
> -
>   /*
>    * A flag to force sched domain rebuild at the end of an operation.
>    * It can be set in
> @@ -219,7 +216,7 @@ static struct cpuset top_cpuset = {
>   		 BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
>   	.partition_root_state = PRS_ROOT,
>   	.relax_domain_level = -1,
> -	.remote_sibling = LIST_HEAD_INIT(top_cpuset.remote_sibling),
> +	.remote_partition = false,
I forgot to notify you that this init is also not needed. Anyway, this 
is a minor issue.
>   };
>   
>   /*
> @@ -1572,7 +1569,7 @@ static int compute_trialcs_excpus(struct cpuset *trialcs, struct cpuset *cs)
>   
>   static inline bool is_remote_partition(struct cpuset *cs)
>   {
> -	return !list_empty(&cs->remote_sibling);
> +	return cs->remote_partition;
>   }
>   
>   static inline bool is_local_partition(struct cpuset *cs)
> @@ -1621,7 +1618,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   
>   	spin_lock_irq(&callback_lock);
>   	partition_xcpus_add(new_prs, NULL, tmp->new_cpus);
> -	list_add(&cs->remote_sibling, &remote_children);
> +	cs->remote_partition = true;
>   	cpumask_copy(cs->effective_xcpus, tmp->new_cpus);
>   	spin_unlock_irq(&callback_lock);
>   	update_isolation_cpumasks();
> @@ -1651,7 +1648,7 @@ static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
>   	WARN_ON_ONCE(!cpumask_subset(cs->effective_xcpus, subpartitions_cpus));
>   
>   	spin_lock_irq(&callback_lock);
> -	list_del_init(&cs->remote_sibling);
> +	cs->remote_partition = false;
>   	partition_xcpus_del(cs->partition_root_state, NULL, cs->effective_xcpus);
>   	if (cs->prs_err)
>   		cs->partition_root_state = -cs->partition_root_state;
> @@ -3603,7 +3600,6 @@ cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
>   	__set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
>   	fmeter_init(&cs->fmeter);
>   	cs->relax_domain_level = -1;
> -	INIT_LIST_HEAD(&cs->remote_sibling);
>   
>   	/* Set CS_MEMORY_MIGRATE for default hierarchy */
>   	if (cpuset_v2())
> @@ -3874,7 +3870,6 @@ int __init cpuset_init(void)
>   	nodes_setall(top_cpuset.effective_mems);
>   
>   	fmeter_init(&top_cpuset.fmeter);
> -	INIT_LIST_HEAD(&remote_children);
>   
>   	BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));
>   
Reviewed-by: Waiman Long <longman@redhat.com>