Re: [PATCH v2 1/5] drm/ttm: add ttm_device_prepare_hibernation() api

[Matthew Brost <matthew.brost@intel.com>]

On Sun, Jul 06, 2025 at 04:44:27PM -0400, Mario Limonciello wrote:
> On 7/4/2025 6:12 AM, Samuel Zhang wrote:
> > This new api is used for hibernation to move GTT BOs to shmem after
> > VRAM eviction. shmem will be flushed to swap disk later to reduce
> > the system memory usage for hibernation.
> > 
> > Signed-off-by: Samuel Zhang <guoqing.zhang@amd.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_device.c | 29 +++++++++++++++++++++++++++++
> >   include/drm/ttm/ttm_device.h     |  1 +
> >   2 files changed, 30 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
> > index 02e797fd1891..19ab35ffeead 100644
> > --- a/drivers/gpu/drm/ttm/ttm_device.c
> > +++ b/drivers/gpu/drm/ttm/ttm_device.c
> > @@ -123,6 +123,35 @@ static int ttm_global_init(void)
> >   	return ret;
> >   }
> > +/**
> > + * move GTT BOs to shmem for hibernation.
> > + *
> > + * returns 0 on success, negative on failure.
> > + */
> > +int ttm_device_prepare_hibernation(void)
> > +{
> > +	struct ttm_operation_ctx ctx = {
> > +		.interruptible = false,
> > +		.no_wait_gpu = false,
> > +		.force_alloc = true
> > +	};
> > +	struct ttm_global *glob = &ttm_glob;
> > +	struct ttm_device *bdev;
> > +	int ret = 0;
> > +
> > +	mutex_lock(&ttm_global_mutex);
> > +	list_for_each_entry(bdev, &glob->device_list, device_list) {
> > +		do {
> > +			ret = ttm_device_swapout(bdev, &ctx, GFP_KERNEL);
> > +		} while (ret > 0);
> > +		if (ret < 0)
> > +			break;
> > +	}
> > +	mutex_unlock(&ttm_global_mutex);
> > +	return ret;
> 
> I'd personally rather see scoped guard here so you can return immediately
> and the guard will clean up but up to Christian what he thinks.
> 
> int ret;
> 
> scoped_guard(mutex, &ttm_global_mutex) {

guard(mutex)(&ttm_global_mutex) would be more apporiate for this as the
scope of the guard is the entire function.

Matt

> 	list_for_each_entry(bdev, &glob->device_list, device_list) {
> 		do {
> 			ret = ttm_device_swapout(bdev, &ctx, GFP_KERNEL);
> 		} while (ret > 0);
> 		if (ret)
> 			return ret;
> }
> 
> return 0;
> 
> > +}
> > +EXPORT_SYMBOL(ttm_device_prepare_hibernation);
> > +
> >   /*
> >    * A buffer object shrink method that tries to swap out the first
> >    * buffer object on the global::swap_lru list.
> > diff --git a/include/drm/ttm/ttm_device.h b/include/drm/ttm/ttm_device.h
> > index 39b8636b1845..b45498b398dd 100644
> > --- a/include/drm/ttm/ttm_device.h
> > +++ b/include/drm/ttm/ttm_device.h
> > @@ -272,6 +272,7 @@ struct ttm_device {
> >   int ttm_global_swapout(struct ttm_operation_ctx *ctx, gfp_t gfp_flags);
> >   int ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
> >   		       gfp_t gfp_flags);
> > +int ttm_device_prepare_hibernation(void);
> >   static inline struct ttm_resource_manager *
> >   ttm_manager_type(struct ttm_device *bdev, int mem_type)
>