[PATCH v3 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio

From: Jingbo Xu <jefflexu@linux.alibaba.com>
To: shr@devkernel.io, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	joseph.qi@linux.alibaba.com, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, willy@infradead.org
Subject: [PATCH v3 2/2] mm: fix arithmetic for max_prop_frac when setting max_ratio
Date: Tue, 19 Dec 2023 22:25:08 +0800	[thread overview]
Message-ID: <20231219142508.86265-3-jefflexu@linux.alibaba.com> (raw)
In-Reply-To: <20231219142508.86265-1-jefflexu@linux.alibaba.com>

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%.

Fixes: efc3e6ad53ea ("mm: split off __bdi_set_max_ratio() function")
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
 mm/page-writeback.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2140382dd768..05e5c425b3ff 100644
--- 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);
 
-- 
2.19.1.6.gb485710b

