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

[Chen Ridong]

On 2025/11/11 12:34, Waiman Long wrote:
> On 11/9/25 8:52 PM, Chen Ridong wrote:
>> From: Chen Ridong <chenridong@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> ---
>>   kernel/cgroup/cpuset-internal.h |  4 ++--
>>   kernel/cgroup/cpuset.c          | 14 +++++---------
>>   2 files changed, 7 insertions(+), 11 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
>> index 5cac42c5fd97..7308e8bc4dde 100644
>> --- a/kernel/cgroup/cpuset-internal.h
>> +++ b/kernel/cgroup/cpuset-internal.h
>> @@ -172,8 +172,8 @@ 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;
>> +    /* Whether cpuset is a remote partition */
>> +    bool remote_partition;
>>   
> 
> The original purpose of adding a linked list for remote children is to enable us iterate the list of
> remote children when needed. This capability is not currently being used. So we can simplify it for
> now, but I would like to add a comment saying that we can switch it back to a list in case we need
> to iterate the remote children list in the future. Also I would suggest moving the bool up before
> partition_file to reduce the number of holes in the cpuset structure.
> 

Thanks, will update.

> 
>>       /* 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..c357bfb69fe2 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,
>>   };
>>     /*
>> @@ -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 +3600,7 @@ 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);
>> +    cs->remote_partition = false;
>>   
> 
> We don't need to initialize remote_partition here as the structure is zalloc'ed.
> 

Thanks, will update.

> 
>>       /* Set CS_MEMORY_MIGRATE for default hierarchy */
>>       if (cpuset_v2())
>> @@ -3874,7 +3871,6 @@ 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));
>>   
> 

-- 
Best regards,
Ridong