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[PATCH 3/3] cgroup: use nodes_and() output where appropriate

Yury Norov posted 3 patches 3 weeks, 4 days ago
[PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Yury Norov 3 weeks, 4 days ago 
Now that nodes_and() returns true if the result nodemask is not empty,
drop useless nodes_intersects() in guarantee_online_mems() and
nodes_empty() in update_nodemasks_hier(), which both are O(N).

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 kernel/cgroup/cpuset.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 3e8cc34d8d50..e962efbb300d 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -456,9 +456,8 @@ static void guarantee_active_cpus(struct task_struct *tsk,
  */
 static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 {
-	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
+	while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]))
 		cs = parent_cs(cs);
-	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
 }
 
 /**
@@ -2862,13 +2861,13 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
 		struct cpuset *parent = parent_cs(cp);
 
-		nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
+		bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
 
 		/*
 		 * If it becomes empty, inherit the effective mask of the
 		 * parent, which is guaranteed to have some MEMs.
 		 */
-		if (is_in_v2_mode() && nodes_empty(*new_mems))
+		if (is_in_v2_mode() && !has_mems)
 			*new_mems = parent->effective_mems;
 
 		/* Skip the whole subtree if the nodemask remains the same. */
-- 
2.43.0
Re: [PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Tejun Heo 3 weeks, 2 days ago 
On Wed, Jan 14, 2026 at 12:22:15PM -0500, Yury Norov wrote:
> Now that nodes_and() returns true if the result nodemask is not empty,
> drop useless nodes_intersects() in guarantee_online_mems() and
> nodes_empty() in update_nodemasks_hier(), which both are O(N).
> 
> Signed-off-by: Yury Norov <ynorov@nvidia.com>

Acked-by: Tejun Heo <tj@kernel.org>

Please feel free to route together with the prerequisite patches.

Thanks.

-- 
tejun
Re: [PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Waiman Long 3 weeks, 4 days ago 
On 1/14/26 12:22 PM, Yury Norov wrote:
> Now that nodes_and() returns true if the result nodemask is not empty,
> drop useless nodes_intersects() in guarantee_online_mems() and
> nodes_empty() in update_nodemasks_hier(), which both are O(N).
>
> Signed-off-by: Yury Norov <ynorov@nvidia.com>
> ---
>   kernel/cgroup/cpuset.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 3e8cc34d8d50..e962efbb300d 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -456,9 +456,8 @@ static void guarantee_active_cpus(struct task_struct *tsk,
>    */
>   static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
>   {
> -	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
> +	while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]))
>   		cs = parent_cs(cs);
> -	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
>   }
>   
>   /**
> @@ -2862,13 +2861,13 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
>   	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
>   		struct cpuset *parent = parent_cs(cp);
>   
> -		nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
> +		bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
>   
>   		/*
>   		 * If it becomes empty, inherit the effective mask of the
>   		 * parent, which is guaranteed to have some MEMs.
>   		 */
> -		if (is_in_v2_mode() && nodes_empty(*new_mems))
> +		if (is_in_v2_mode() && !has_mems)
>   			*new_mems = parent->effective_mems;
>   
>   		/* Skip the whole subtree if the nodemask remains the same. */
Reviewed-by: Waiman Long <longman@redhat.com>
Re: [PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Chen Ridong 3 weeks, 4 days ago 

On 2026/1/15 6:33, Waiman Long wrote:
> On 1/14/26 12:22 PM, Yury Norov wrote:
>> Now that nodes_and() returns true if the result nodemask is not empty,
>> drop useless nodes_intersects() in guarantee_online_mems() and
>> nodes_empty() in update_nodemasks_hier(), which both are O(N).
>>
>> Signed-off-by: Yury Norov <ynorov@nvidia.com>
>> ---
>>   kernel/cgroup/cpuset.c | 7 +++----
>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 3e8cc34d8d50..e962efbb300d 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -456,9 +456,8 @@ static void guarantee_active_cpus(struct task_struct *tsk,
>>    */
>>   static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
>>   {
>> -    while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
>> +    while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]))
>>           cs = parent_cs(cs);
>> -    nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
>>   }
>>     /**
>> @@ -2862,13 +2861,13 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
>>       cpuset_for_each_descendant_pre(cp, pos_css, cs) {
>>           struct cpuset *parent = parent_cs(cp);
>>   -        nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
>> +        bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
>>             /*
>>            * If it becomes empty, inherit the effective mask of the
>>            * parent, which is guaranteed to have some MEMs.
>>            */
>> -        if (is_in_v2_mode() && nodes_empty(*new_mems))
>> +        if (is_in_v2_mode() && !has_mems)
>>               *new_mems = parent->effective_mems;
>>             /* Skip the whole subtree if the nodemask remains the same. */
> Reviewed-by: Waiman Long <longman@redhat.com>
> 

Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>

-- 
Best regards,
Ridong
Re: [PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Michal Koutný 3 weeks, 4 days ago 
On Wed, Jan 14, 2026 at 12:22:15PM -0500, Yury Norov <ynorov@nvidia.com> wrote:
> Now that nodes_and() returns true if the result nodemask is not empty,
> drop useless nodes_intersects() in guarantee_online_mems() and
> nodes_empty() in update_nodemasks_hier(), which both are O(N).
> 
> Signed-off-by: Yury Norov <ynorov@nvidia.com>
> ---
>  kernel/cgroup/cpuset.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Nice improvement.

Reviewed-by: Michal Koutný <mkoutny@suse.com>
Re: [PATCH 3/3] cgroup: use nodes_and() output where appropriate
Posted by Gregory Price 3 weeks, 4 days ago 
On Wed, Jan 14, 2026 at 12:22:15PM -0500, Yury Norov wrote:
> Now that nodes_and() returns true if the result nodemask is not empty,
> drop useless nodes_intersects() in guarantee_online_mems() and
> nodes_empty() in update_nodemasks_hier(), which both are O(N).
> 
> Signed-off-by: Yury Norov <ynorov@nvidia.com>

This is a nice simplification, thank you!

Reviewed-by: Gregory Price <gourry@gourry.net>

Patchew 2.1-devel-b67e4c2

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