On Tue, Dec 19, 2023 at 01:58:21PM +0800, Jingbo Xu wrote:
> On 12/19/23 12:06 PM, Matthew Wilcox wrote:
> > On Tue, Dec 19, 2023 at 10:42:46AM +0800, Jingbo Xu wrote:
> >> } else {
> >> bdi->max_ratio = max_ratio;
> >> - bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
> >> + bdi->max_prop_frac = div64_u64(FPROP_FRAC_BASE * max_ratio,
> >> + 100 * BDI_RATIO_SCALE);
> >> }
> >
> > Why use div64_u64 here?
> >
> > FPROP_FRAC_BASE is an unsigned long. max_ratio is an unsigned int, so
> > the numerator is an unsigned long. BDI_RATIO_SCALE is 10,000, so the
> > numerator is an unsigned int. There's no 64-bit arithmetic needed here.
>
> Yes, div64_u64() is actually not needed here. So it seems
>
> bdi->max_prop_frac = FPROP_FRAC_BASE * max_ratio / 100 / BDI_RATIO_SCALE;
>
> is adequate?
I'd rather spell that as:
bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) /
(100 * BDI_RATIO_SCALE);
It's closer to how you'd write it out mathematically and so it reads
more easily. At least for me.
