linux-kernel - Re: [PATCH -next 1/2] PM: hibernate: fix spelling mistake for annotation

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Date:   Thu, 3 Nov 2022 17:25:43 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     TGSP <tgsp002@...il.com>
Cc:     rafael@...nel.org, len.brown@...el.com, pavel@....cz,
        huanglei@...inos.cn, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, xiongxin <xiongxin@...inos.cn>,
        stable@...r.kernel.org
Subject: Re: [PATCH -next 1/2] PM: hibernate: fix spelling mistake for annotation

On Tue, Nov 1, 2022 at 3:28 AM TGSP <tgsp002@...il.com> wrote:
>
> From: xiongxin <xiongxin@...inos.cn>
>
> The actual calculation formula in the code below is:
>
> max_size = (count - (size + PAGES_FOR_IO)) / 2
>             - 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE);
>
> But function comments are written differently, the comment is wrong?

It is, and it is more serious than just a spelling mistake.

> By the way, what exactly do the "/ 2" and "2 *" mean?

Every page in the image is a copy of an existing allocated page, so
room needs to be made for the two, except for the "IO pages" and
metadata pages that are not copied.  Hence, the division by 2.

Now, the "reserved_size" pages will be allocated right before creating
the image and there will be a copy of each of them in the image, so
there needs to be room for twice as many.

I'll adjust the changelog and queue up the path for 6.2.

> Cc: stable@...r.kernel.org

I'll add a Fixes tag instead.

> Signed-off-by: xiongxin <xiongxin@...inos.cn>
> ---
>  kernel/power/snapshot.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 2a406753af90..c20ca5fb9adc 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1723,8 +1723,8 @@ static unsigned long minimum_image_size(unsigned long saveable)
>   * /sys/power/reserved_size, respectively).  To make this happen, we compute the
>   * total number of available page frames and allocate at least
>   *
> - * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2
> - *  + 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
> + * ([page frames total] - PAGES_FOR_IO - [metadata pages]) / 2
> + *  - 2 * DIV_ROUND_UP(reserved_size, PAGE_SIZE)
>   *
>   * of them, which corresponds to the maximum size of a hibernation image.
>   *
> --
> 2.25.1
>