[PATCH v3 3/5] PM: hibernate: shrink shmem pages after dev_pm_ops.prepare()

[Rafael J. Wysocki]

On Tue, Jul 8, 2025 at 4:28 PM Mario Limonciello
<mario.limonciello at amd.com> wrote:
>
> On 7/8/2025 3:42 AM, Samuel Zhang 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>
>
> AFAICT this didn't tangibly change and was just reordered in the series,
> I think you should carry Rafael's A-b tag forward.

Yes, please.

> > ---
> >   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();
> >
>