The patch titled
Subject: mm/page-writeback.c: use div64_ul() for u64-by-unsigned-long divide
has been added to the -mm tree. Its filename is
mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide.patch
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------------------------------------------------------
From: Wen Yang <wenyang@xxxxxxxxxxxxxxxxx>
Subject: 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().
Link: http://lkml.kernel.org/r/20200102081442.8273-3-wenyang@xxxxxxxxxxxxxxxxx
Signed-off-by: Wen Yang <wenyang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/page-writeback.c~mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide
+++ a/mm/page-writeback.c
@@ -766,7 +766,7 @@ static unsigned long __wb_calc_thresh(st
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(st
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);
_
Patches currently in -mm which might be from wenyang@xxxxxxxxxxxxxxxxx are
mm-page-writebackc-avoid-potential-division-by-zero-in-wb_min_max_ratio.patch
mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide.patch
mm-page-writebackc-improve-arithmetic-divisions.patch
