linux-kernel - Re: [PATCH -next 2/2] PM: hibernate: add check of preallocate mem for image size pages

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Date:   Thu, 3 Nov 2022 17:47:43 +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 2/2] PM: hibernate: add check of preallocate mem for
 image size pages

On Tue, Nov 1, 2022 at 3:28 AM TGSP <tgsp002@...il.com> wrote:
>
> From: xiongxin <xiongxin@...inos.cn>
>
> Added a check on the return value of preallocate_image_highmem(). If
> memory preallocate is insufficient, S4 cannot be done;
>
> I am playing 4K video on a machine with AMD or other graphics card and
> only 8GiB memory, and the kernel is not configured with CONFIG_HIGHMEM.
> When doing the S4 test, the analysis found that when the pages get from
> minimum_image_size() is large enough, The preallocate_image_memory() and
> preallocate_image_highmem() calls failed to obtain enough memory. Add
> the judgment that memory preallocate is insufficient;
>
> "pages -= free_unnecessary_pages()" below will let pages to drop a lot,
> so I wonder if it makes sense to add a judgment here.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: xiongxin <xiongxin@...inos.cn>
> Signed-off-by: huanglei <huanglei@...inos.cn>
> ---
>  kernel/power/snapshot.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index c20ca5fb9adc..670abf89cf31 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1738,6 +1738,7 @@ int hibernate_preallocate_memory(void)
>         struct zone *zone;
>         unsigned long saveable, size, max_size, count, highmem, pages = 0;
>         unsigned long alloc, save_highmem, pages_highmem, avail_normal;
> +       unsigned long size_highmem;

Please define this in the block where it will be used.

>         ktime_t start, stop;
>         int error;
>
> @@ -1863,7 +1864,13 @@ int hibernate_preallocate_memory(void)
>                 pages_highmem += size;

The line above can be dropped.

>                 alloc -= size;
>                 size = preallocate_image_memory(alloc, avail_normal);
> -               pages_highmem += preallocate_image_highmem(alloc - size);
> +               size_highmem += preallocate_image_highmem(alloc - size);

Did you mean "="?

Assuming you did, this could be

        size_highmem = size + preallocate_image_highmem(alloc - size);
        if (size_highmem < alloc) {

> +               if (size_highmem < (alloc - size)) {

The inner parens were not necessary.

> +                       pr_err("Image allocation is %lu pages short, exit\n",
> +                               alloc - size - pages_highmem);
> +                       goto err_out;
> +               }
> +               pages_highmem += size_highmem;
>                 pages += pages_highmem + size;
>         }
>
> --

But overall it would be better to avoid bailing out.