mm: fix arithmetic for max_prop_frac when setting max_ratio

Since now bdi->max_ratio is part per million, fix the wrong arithmetic for max_prop_frac when setting max_ratio. Otherwise the miscalculated max_prop_frac will affect the incrementing of writeout completion count when max_ratio is not 100%. Link: https://lkml.kernel.org/r/20231219142508.86265-3-jefflexu@linux.alibaba.com Fixes: efc3e6a ("mm: split off __bdi_set_max_ratio() function") Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com> Cc: Joseph Qi <joseph.qi@linux.alibaba.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Stefan Roesch <shr@devkernel.io> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: lostjeffle

mm/page-writeback.c

@@ -728,7 +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 = (FPROP_FRAC_BASE * max_ratio) /
+(100 * BDI_RATIO_SCALE);
 }
 spin_unlock_bh(&bdi_lock);