2020-01-03 15:57:18

by Wen Yang

Subject: [PATCH] kernel/power/snapshot.c: improve arithmetic divisions

do_div() does a 64-by-32 division. Use div64_u64() instead of
do_div() if the divisor is u64, to avoid truncation to 32-bit.
This change also cleans up code a tad.

Signed-off-by: Wen Yang <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: [email protected]
Cc: [email protected]
---
kernel/power/snapshot.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 26b9168..8a6eaf7 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1566,9 +1566,7 @@ static unsigned long preallocate_image_highmem(unsigned long nr_pages)
*/
static unsigned long __fraction(u64 x, u64 multiplier, u64 base)
{
- x *= multiplier;
- do_div(x, base);
- return (unsigned long)x;
+ return div64_u64(x * multiplier, base);
}

static unsigned long preallocate_highmem_fraction(unsigned long nr_pages,
--
1.8.3.1

2020-01-07 12:09:11

by Rafael J. Wysocki

Subject: Re: [PATCH] kernel/power/snapshot.c: improve arithmetic divisions

On Fri, Jan 3, 2020 at 4:55 PM Wen Yang <[email protected]> wrote:
>
> do_div() does a 64-by-32 division. Use div64_u64() instead of
> do_div() if the divisor is u64, to avoid truncation to 32-bit.
> This change also cleans up code a tad.
>
> Signed-off-by: Wen Yang <[email protected]>
> Cc: "Rafael J. Wysocki" <[email protected]>
> Cc: Len Brown <[email protected]>
> Cc: Pavel Machek <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> ---
> kernel/power/snapshot.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 26b9168..8a6eaf7 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1566,9 +1566,7 @@ static unsigned long preallocate_image_highmem(unsigned long nr_pages)
> */
> static unsigned long __fraction(u64 x, u64 multiplier, u64 base)
> {
> - x *= multiplier;
> - do_div(x, base);
> - return (unsigned long)x;
> + return div64_u64(x * multiplier, base);
> }
>
> static unsigned long preallocate_highmem_fraction(unsigned long nr_pages,
> --

Applied as 5.6 material under a new subject ("PM: hibernate: improve
arithmetic division in preallocate_highmem_fraction()"), thanks!