Re: [patch 05/25] debugobjects: Dont free objects directly on CPU hotplug

[Leizhen (ThunderTown)]

On 2024/10/8 0:49, Thomas Gleixner wrote:
> Freeing the per CPU pool of the unplugged CPU directly is suboptimal as the
> objects can be reused in the real pool if there is room. Aside of that this
> gets the accounting wrong.
> 
> Use the regular free path, which allows reuse and has the accounting correct.

Reviewed-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>

> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  lib/debugobjects.c |   27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -430,27 +430,28 @@ static void free_object(struct debug_obj
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> -static int object_cpu_offline(unsigned int cpu)
> +static void put_objects(struct hlist_head *list)
>  {
> -	struct debug_percpu_free *percpu_pool;
>  	struct hlist_node *tmp;
>  	struct debug_obj *obj;
> -	unsigned long flags;
>  
> -	/* Remote access is safe as the CPU is dead already */
> -	percpu_pool = per_cpu_ptr(&percpu_obj_pool, cpu);
> -	hlist_for_each_entry_safe(obj, tmp, &percpu_pool->free_objs, node) {
> +	/*
> +	 * Using free_object() puts the objects into reuse or schedules
> +	 * them for freeing and it get's all the accounting correct.
> +	 */
> +	hlist_for_each_entry_safe(obj, tmp, list, node) {
>  		hlist_del(&obj->node);
> -		kmem_cache_free(obj_cache, obj);
> +		free_object(obj);
>  	}
> +}
>  
> -	raw_spin_lock_irqsave(&pool_lock, flags);
> -	obj_pool_used -= percpu_pool->obj_free;
> -	debug_objects_freed += percpu_pool->obj_free;
> -	raw_spin_unlock_irqrestore(&pool_lock, flags);
> -
> -	percpu_pool->obj_free = 0;
> +static int object_cpu_offline(unsigned int cpu)
> +{
> +	/* Remote access is safe as the CPU is dead already */
> +	struct debug_percpu_free *pcp = per_cpu_ptr(&percpu_obj_pool, cpu);
>  
> +	put_objects(&pcp->free_objs);
> +	pcp->obj_free = 0;
>  	return 0;
>  }
>  #endif
> 
> 
> .
> 

-- 
Regards,
  Zhen Lei