Messages in this thread | | | Date | Tue, 19 Dec 2023 04:06:34 +0000 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio |
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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.
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