Messages in this thread | | | Date | Tue, 19 Dec 2023 13:58:21 +0800 | Subject | Re: [PATCH v2 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio | From | Jingbo Xu <> |
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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?
-- Thanks, Jingbo
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