Re: [PATCH v2] PM: hibernate: call preallocate_image after freeze prepare

[Rafael J. Wysocki]

On Thu, Mar 26, 2026 at 12:37 PM Matthew Leach
<matthew.leach@xxxxxxxxxxxxx> wrote:
>
> Certain drivers release resources (pinned pages, etc.) into system
> memory during the prepare freeze PM op, making them swappable.
> Currently, hibernate_preallocate_memory is called before prepare freeze,
> so those drivers have no opportunity to release resources first. If a
> driver is holding a large amount of unswappable system RAM, this can
> cause hibernate_preallocate_memory to fail.
>
> Move the call to hibernate_preallocate_memory after prepare freeze.
> According to the documentation for the prepare callback, devices should
> be left in a usable state, so storage drivers should still be able to
> service I/O requests. This allows drivers to release unswappable
> resources prior to preallocation, so they can be swapped out through
> hibernate_preallocate_memory's reclaim path. Also remove
> shrink_shmem_memory since hibernate_preallocate_memory will have
> reclaimed enough memory for the hibernation image.
>
> Signed-off-by: Matthew Leach <matthew.leach@xxxxxxxxxxxxx>
> ---
> Changes in v2:
> - Removed shrink_shmem_memory.
> - Fixed missing call to dpm_prepare in error path.
> - Link to v1: https://lore.kernel.org/r/20260321-hibernation-fixes-v1-1-5fe9637b6ff9@xxxxxxxxxxxxx
> ---
>  kernel/power/hibernate.c | 46 +++++++++-------------------------------------
>  1 file changed, 9 insertions(+), 37 deletions(-)
>
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index af8d07bafe02..39b0a8ea4024 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -392,23 +392,6 @@ 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.
> @@ -425,14 +408,9 @@ int hibernation_snapshot(int platform_mode)
>         if (error)
>                 goto Close;
>
> -       /* Preallocate image memory before shutting down devices. */
> -       error = hibernate_preallocate_memory();
> -       if (error)
> -               goto Close;
> -
>         error = freeze_kernel_threads();
>         if (error)
> -               goto Cleanup;
> +               goto Close;
>
>         if (hibernation_test(TEST_FREEZER)) {
>
> @@ -441,23 +419,17 @@ int hibernation_snapshot(int platform_mode)
>                  * successful freezer test.
>                  */
>                 freezer_test_done = true;
> -               goto Thaw;
> +               goto ThawKThreads;

Do not change the name of this label.

>         }
>
>         error = dpm_prepare(PMSG_FREEZE);
> -       if (error) {
> -               dpm_complete(PMSG_RECOVER);
> +       if (error)
>                 goto Thaw;

But add a new label called "Complete" for this jump.

> -       }
>
> -       /*
> -        * 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();
> +       /* Preallocate image memory before shutting down devices. */
> +       error = hibernate_preallocate_memory();
> +       if (error)
> +               goto Thaw;
>
>         console_suspend_all();
>         pm_restrict_gfp_mask();
> @@ -493,9 +465,9 @@ int hibernation_snapshot(int platform_mode)
>         return error;
>
>   Thaw:

swsusp_free() needs to be called here AFAICS or you'll see memory
allocation failures subsequently in some cases.

> +       dpm_complete(PMSG_RECOVER);
> + ThawKThreads:
>         thaw_kernel_threads();
> - Cleanup:
> -       swsusp_free();
>         goto Close;
>  }
>
>
> ---