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: efc3e6ad53ea ("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>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2140382dd76851ab3d565302c1da0b6ca9a18342..05e5c425b3ff741f41652843ca169662aba32088 100644 (file)
--- a/mm/page-writeback.c
+++ b/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);