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

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Message-ID: <CAJZ5v0j_0iW5k2GJGZ=REYiR29W1BGmNi-7TiXz5jwZ80+FxpQ@mail.gmail.com>
Date:   Tue, 7 Jan 2020 12:43:41 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Wen Yang <wenyang@...ux.alibaba.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/power/snapshot.c: improve arithmetic divisions

On Fri, Jan 3, 2020 at 4:55 PM Wen Yang <wenyang@...ux.alibaba.com> 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 <wenyang@...ux.alibaba.com>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Pavel Machek <pavel@....cz>
> Cc: linux-pm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  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!