On Mon, 18 Dec 2023 11:16:40 +0800 Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
> bdi->[min|max]_ratio are both part per million. Fix the wrong
> arithmetic when setting bdi's min_ratio and max_ratio.
>
> Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function")
> Fixes: 8021fb3232f2 ("mm: split off __bdi_set_min_ratio() function")
As we have two Fixes:, it would be better to have two patches please.
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -692,7 +692,6 @@ static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ra
>
> if (min_ratio > 100 * BDI_RATIO_SCALE)
> return -EINVAL;
> - min_ratio *= BDI_RATIO_SCALE;
>
> spin_lock_bh(&bdi_lock);
> if (min_ratio > bdi->max_ratio) {
> @@ -729,7 +728,8 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra
> ret = -EINVAL;
> } 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,
> + 100UL * BDI_RATIO_SCALE);
> }
> spin_unlock_bh(&bdi_lock);
Does this change have any observable runtime effects? If so, what are they?
