[PATCH 2/3] PM: hibernate: shrink shmem pages after dev_pm_ops.prepare()

[Rafael J. Wysocki]

On Mon, Jun 30, 2025 at 12:41 PM Samuel Zhang <guoqing.zhang at amd.com> wrote:
>
> When hibernate with data center dGPUs, huge number of VRAM data will be
> moved to shmem during dev_pm_ops.prepare(). These shmem pages take a lot
> of system memory so that there's no enough free memory for creating the
> hibernation image. This will cause hibernation fail and abort.
>
> After dev_pm_ops.prepare(), call shrink_all_memory() to force move shmem
> pages to swap disk and reclaim the pages, so that there's enough system
> memory for hibernation image and less pages needed to copy to the image.
>
> This patch can only flush and free about half shmem pages. It will be
> better to flush and free more pages, even all of shmem pages, so that
> there're less pages to be copied to the hibernation image and the overall
> hibernation time can be reduced.
>
> Signed-off-by: Samuel Zhang <guoqing.zhang at amd.com>
> ---
>  kernel/power/hibernate.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 10a01af63a80..913a298c1d01 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -370,6 +370,17 @@ static int create_image(int platform_mode)
>         return error;
>  }
>
> +static void shrink_shmem_memory(void)
> +{
> +       struct sysinfo info;
> +       unsigned long pages, freed;
> +

Please add a comment explaining what is going on here.

> +       si_meminfo(&info);
> +       pages = info.sharedram;
> +       freed = shrink_all_memory(pages);
> +       pr_debug("requested to reclaim %lu pages, freed %lu pages\n", pages, freed);

This message will be hard to decode without any context.

> +}
> +
>  /**
>   * hibernation_snapshot - Quiesce devices and create a hibernation image.
>   * @platform_mode: If set, use platform driver to prepare for the transition.
> @@ -411,6 +422,8 @@ int hibernation_snapshot(int platform_mode)
>                 goto Thaw;
>         }
>

Please add a comment explaining why the below is done.

> +       shrink_shmem_memory();
> +
>         suspend_console();
>         pm_restrict_gfp_mask();
>
> --
> 2.43.5
>
>