Re: [PATCH][RFC] radix-tree.c

[Andrew Morton <akpm@digeo.com>]

Szabolcs Berecz <szabi@mplayerhq.hu> wrote:
>
> 
> With the following patch maxindex is taken from an array instead of
> recalculating it all the time.

Looks good to me.

> +static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH];
> +
>  /*
>   * Radix tree node cache.
>   */
> @@ -126,12 +128,9 @@
>   */
>  static inline unsigned long radix_tree_maxindex(unsigned int height)
>  {
> -	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
> -	unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
> -
> -	if (tmp >= RADIX_TREE_INDEX_BITS)
> -		index = ~0UL;
> -	return index;
> +	if (unlikely(height >= RADIX_TREE_MAX_PATH))
> +		return ~0UL;
> +	return height_to_maxindex[height];

If you make height_to_maxindex[] a bit bigger, and fill it up with ~0UL's,
this comparison can be removed too.

I rather hope that height cannot be larger than RADIX_TREE_MAX_PATH anyway...