Re: [PATCH V6 1/2] percpu_ref: reduce memory footprint of percpu_ref in fast path

[Tejun Heo]

On Wed, Sep 30, 2020 at 04:26:56PM +0800, Ming Lei wrote:
> diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
> index 87d8a38bdea1..1d6ed9ca23dd 100644
> --- a/include/linux/percpu-refcount.h
> +++ b/include/linux/percpu-refcount.h
> @@ -92,18 +92,23 @@ enum {
>  	PERCPU_REF_ALLOW_REINIT	= 1 << 2,
>  };
>  
> -struct percpu_ref {
> +struct percpu_ref_data {
>  	atomic_long_t		count;
> -	/*
> -	 * The low bit of the pointer indicates whether the ref is in percpu
> -	 * mode; if set, then get/put will manipulate the atomic_t.
> -	 */
> -	unsigned long		percpu_count_ptr;
>  	percpu_ref_func_t	*release;
>  	percpu_ref_func_t	*confirm_switch;
>  	bool			force_atomic:1;
>  	bool			allow_reinit:1;
>  	struct rcu_head		rcu;
> +	struct percpu_ref	*ref;
> +};
> +
> +struct percpu_ref {
> +	/*
> +	 * The low bit of the pointer indicates whether the ref is in percpu
> +	 * mode; if set, then get/put will manipulate the atomic_t.
> +	 */
> +	unsigned long		percpu_count_ptr;
> +	struct percpu_ref_data  *data;
>  };

Can you please add a comment explaining why the two structs are split?

Thanks.

-- 
tejun