linux-kernel - [PATCH 2/3] mm/page-writeback.c: use div64

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Date:   Thu,  2 Jan 2020 16:14:41 +0800
From:   Wen Yang <wenyang@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, Qian Cai <cai@....pw>
Cc:     xlpang@...ux.alibaba.com, Wen Yang <wenyang@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] mm/page-writeback.c: use div64_ul() for u64-by-unsigned-long divide

The two variables 'numerator' and 'denominator',
though they are declared as long, they should actually be
unsigned long (according to the implementation of the
fprop_fraction_percpu() function)

And do_div() does a 64-by-32 division, while the divisor
'denominator' is unsigned long, thus 64-bit on 64-bit platforms.
Hence the proper function to call is div64_ul().

Signed-off-by: Wen Yang <wenyang@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Qian Cai <cai@....pw>
Cc: Tejun Heo <tj@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
---
 mm/page-writeback.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2d658b2..c74c6bd 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -766,7 +766,7 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
 	struct wb_domain *dom = dtc_dom(dtc);
 	unsigned long thresh = dtc->thresh;
 	u64 wb_thresh;
-	long numerator, denominator;
+	unsigned long numerator, denominator;
 	unsigned long wb_min_ratio, wb_max_ratio;
 
 	/*
@@ -777,7 +777,7 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
 
 	wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
 	wb_thresh *= numerator;
-	do_div(wb_thresh, denominator);
+	wb_thresh = div64_ul(wb_thresh, denominator);
 
 	wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
 
-- 
1.8.3.1