Re: [patch 3/4] percpu_ida: add an API to return free tags

[Kent Overstreet]

On Fri, Oct 11, 2013 at 03:18:05PM +0800, Shaohua Li wrote:
> add an API to return free tags, blk-mq-tag will use it

Can you explain how this is going to be used? Seems like something that
could be prone to misuse, try and convince me there isn't a better way
to do what it's for.

> 
> Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
> ---
>  include/linux/percpu_ida.h |    1 +
>  lib/percpu_ida.c           |   17 +++++++++++++++++
>  2 files changed, 18 insertions(+)
> 
> Index: master/include/linux/percpu_ida.h
> ===================================================================
> --- master.orig/include/linux/percpu_ida.h	2013-10-11 12:15:06.996416710 +0800
> +++ master/include/linux/percpu_ida.h	2013-10-11 12:15:06.992416749 +0800
> @@ -76,4 +76,5 @@ static inline int percpu_ida_init(struct
>  int percpu_ida_for_each_free(struct percpu_ida *pool,
>  	int (*fn)(int id, void *data), void *data);
>  
> +unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu);
>  #endif /* __PERCPU_IDA_H__ */
> Index: master/lib/percpu_ida.c
> ===================================================================
> --- master.orig/lib/percpu_ida.c	2013-10-11 12:15:06.996416710 +0800
> +++ master/lib/percpu_ida.c	2013-10-11 12:15:06.992416749 +0800
> @@ -371,3 +371,20 @@ out:
>  	return err;
>  }
>  EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
> +
> +/**
> + * percpu_ida_free_tags - return free tags number of a specific cpu or global pool
> + * @pool: pool related
> + * @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
> + *
> + * Note: this just returns a snapshot of free tags number.
> + */
> +unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
> +{
> +	struct percpu_ida_cpu *remote;
> +	if (cpu == nr_cpu_ids)
> +		return pool->nr_free;
> +	remote = per_cpu_ptr(pool->tag_cpu, cpu);
> +	return remote->nr_free;
> +}
> +EXPORT_SYMBOL_GPL(percpu_ida_free_tags);
> 
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