Re: [PATCH 02/16] lib/bitmap: don't call bitmap_set() with len == 0

[Andy Shevchenko]

On Mon, Jul 18, 2022 at 12:28:30PM -0700, Yury Norov wrote:
> bitmap_parselist() format allows passing 0-length regions, but because
> len == 0 is not covered by small_const_nbits() macro, we have to call
> __bitmap_set() and do some prologue calculations just for nothing.

...

>  static void bitmap_set_region(const struct region *r, unsigned long *bitmap)
>  {
> -	unsigned int start;
> +	unsigned int start, len;
>  
> -	for (start = r->start; start <= r->end; start += r->group_len)
> -		bitmap_set(bitmap, start, min(r->end - start + 1, r->off));
> +	for (start = r->start; start <= r->end; start += r->group_len) {
> +		len = min(r->end - start + 1, r->off);
> +		if (len > 0)
> +			bitmap_set(bitmap, start, len);

Maybe I'm missing something, but how small_const_nbits() can possible be useful
here? I mean in which cases the compiler would be able to prove that len is a
const with < sizeof(unsigned long) bits?

> +	}
>  }

-- 
With Best Regards,
Andy Shevchenko