linux-kernel - Re: [PATCH v3 3/5] PM: hibernate: shrink shmem pages after dev_pm

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Message-ID: <CAJZ5v0iscejFdRXQAPkzdN0xBdZDnx5LzVvsN2SGC0ByBku85A@mail.gmail.com>
Date: Tue, 8 Jul 2025 16:33:04 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Samuel Zhang <guoqing.zhang@....com>, alexander.deucher@....com, 
	christian.koenig@....com, rafael@...nel.org, len.brown@...el.com, 
	pavel@...nel.org, gregkh@...uxfoundation.org, dakr@...nel.org, 
	airlied@...il.com, simona@...ll.ch, ray.huang@....com, matthew.auld@...el.com, 
	matthew.brost@...el.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, lijo.lazar@....com, 
	victor.zhao@....com, haijun.chang@....com, Qing.Ma@....com, 
	Owen.Zhang2@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 3/5] PM: hibernate: shrink shmem pages after dev_pm_ops.prepare()

On Tue, Jul 8, 2025 at 4:28 PM Mario Limonciello
<mario.limonciello@....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@....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();
> >
>