[PATCH v2 3/5] PM: hibernate: shrink shmem pages after dev_pm_ops.prepare()

[Rafael J. Wysocki]

On Fri, Jul 4, 2025 at 12:14 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>

No fundamental objections from me, so

Acked-by: Rafael J. Wysocki <rafael at kernel.org>

> ---
>  kernel/power/hibernate.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 10a01af63a80..7ae9d9a7aa1d 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -370,6 +370,23 @@ static int create_image(int platform_mode)
>         return error;
>  }
>
> +static void shrink_shmem_memory(void)
> +{
> +       struct sysinfo info;
> +       unsigned long nr_shmem_pages, nr_freed_pages;
> +
> +       si_meminfo(&info);
> +       nr_shmem_pages = info.sharedram; /* current page count used for shmem */
> +       /*
> +        * The intent is to reclaim all shmem pages. Though shrink_all_memory() can
> +        * only reclaim about half of them, it's enough for creating the hibernation
> +        * image.
> +        */
> +       nr_freed_pages = shrink_all_memory(nr_shmem_pages);
> +       pr_debug("requested to reclaim %lu shmem pages, actually freed %lu pages\n",
> +                       nr_shmem_pages, nr_freed_pages);
> +}
> +
>  /**
>   * hibernation_snapshot - Quiesce devices and create a hibernation image.
>   * @platform_mode: If set, use platform driver to prepare for the transition.
> @@ -411,6 +428,15 @@ int hibernation_snapshot(int platform_mode)
>                 goto Thaw;
>         }
>
> +       /*
> +        * Device drivers may move lots of data to shmem in dpm_prepare(). The shmem
> +        * pages will use lots of system memory, causing hibernation image creation
> +        * fail due to insufficient free memory.
> +        * This call is to force flush the shmem pages to swap disk and reclaim
> +        * the system memory so that image creation can succeed.
> +        */
> +       shrink_shmem_memory();
> +
>         suspend_console();
>         pm_restrict_gfp_mask();
>
> --
> 2.43.5
>