Re: [PATCH v2 24/47] drm/panfrost: dynamically allocate the drm-panfrost shrinker

[Steven Price]

On 24/07/2023 10:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the drm-panfrost shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct panfrost_device.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

One nit below, but otherwise:

Reviewed-by: Steven Price <steven.price@xxxxxxx>

> ---
>  drivers/gpu/drm/panfrost/panfrost_device.h    |  2 +-
>  drivers/gpu/drm/panfrost/panfrost_drv.c       |  6 +++-
>  drivers/gpu/drm/panfrost/panfrost_gem.h       |  2 +-
>  .../gpu/drm/panfrost/panfrost_gem_shrinker.c  | 32 ++++++++++++-------
>  4 files changed, 27 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> index b0126b9fbadc..e667e5689353 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> @@ -118,7 +118,7 @@ struct panfrost_device {
>  
>  	struct mutex shrinker_lock;
>  	struct list_head shrinker_list;
> -	struct shrinker shrinker;
> +	struct shrinker *shrinker;
>  
>  	struct panfrost_devfreq pfdevfreq;
>  };
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index bbada731bbbd..f705bbdea360 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -598,10 +598,14 @@ static int panfrost_probe(struct platform_device *pdev)
>  	if (err < 0)
>  		goto err_out1;
>  
> -	panfrost_gem_shrinker_init(ddev);
> +	err = panfrost_gem_shrinker_init(ddev);
> +	if (err)
> +		goto err_out2;
>  
>  	return 0;
>  
> +err_out2:
> +	drm_dev_unregister(ddev);
>  err_out1:
>  	pm_runtime_disable(pfdev->dev);
>  	panfrost_device_fini(pfdev);
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index ad2877eeeccd..863d2ec8d4f0 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -81,7 +81,7 @@ panfrost_gem_mapping_get(struct panfrost_gem_object *bo,
>  void panfrost_gem_mapping_put(struct panfrost_gem_mapping *mapping);
>  void panfrost_gem_teardown_mappings_locked(struct panfrost_gem_object *bo);
>  
> -void panfrost_gem_shrinker_init(struct drm_device *dev);
> +int panfrost_gem_shrinker_init(struct drm_device *dev);
>  void panfrost_gem_shrinker_cleanup(struct drm_device *dev);
>  
>  #endif /* __PANFROST_GEM_H__ */
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> index bf0170782f25..9a90dfb5301f 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> @@ -18,8 +18,7 @@
>  static unsigned long
>  panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>  {
> -	struct panfrost_device *pfdev =
> -		container_of(shrinker, struct panfrost_device, shrinker);
> +	struct panfrost_device *pfdev = shrinker->private_data;
>  	struct drm_gem_shmem_object *shmem;
>  	unsigned long count = 0;
>  
> @@ -65,8 +64,7 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj)
>  static unsigned long
>  panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>  {
> -	struct panfrost_device *pfdev =
> -		container_of(shrinker, struct panfrost_device, shrinker);
> +	struct panfrost_device *pfdev = shrinker->private_data;
>  	struct drm_gem_shmem_object *shmem, *tmp;
>  	unsigned long freed = 0;
>  
> @@ -97,13 +95,24 @@ panfrost_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>   *
>   * This function registers and sets up the panfrost shrinker.
>   */
> -void panfrost_gem_shrinker_init(struct drm_device *dev)
> +int panfrost_gem_shrinker_init(struct drm_device *dev)
>  {
>  	struct panfrost_device *pfdev = dev->dev_private;
> -	pfdev->shrinker.count_objects = panfrost_gem_shrinker_count;
> -	pfdev->shrinker.scan_objects = panfrost_gem_shrinker_scan;
> -	pfdev->shrinker.seeks = DEFAULT_SEEKS;
> -	WARN_ON(register_shrinker(&pfdev->shrinker, "drm-panfrost"));
> +
> +	pfdev->shrinker = shrinker_alloc(0, "drm-panfrost");
> +	if (!pfdev->shrinker) {
> +		WARN_ON(1);

I don't think this WARN_ON is particularly useful - if there's a failed
memory allocation we should see output from the kernel anyway. And we're
changing the semantics from "continue just without a shrinker" (which
argueably justifies the warning) to "probe fails, device doesn't work"
which will be obvious to the user so I don't feel we need the additional
warn.

> +		return -ENOMEM;
> +	}
> +
> +	pfdev->shrinker->count_objects = panfrost_gem_shrinker_count;
> +	pfdev->shrinker->scan_objects = panfrost_gem_shrinker_scan;
> +	pfdev->shrinker->seeks = DEFAULT_SEEKS;
> +	pfdev->shrinker->private_data = pfdev;
> +
> +	shrinker_register(pfdev->shrinker);
> +
> +	return 0;
>  }
>  
>  /**
> @@ -116,7 +125,6 @@ void panfrost_gem_shrinker_cleanup(struct drm_device *dev)
>  {
>  	struct panfrost_device *pfdev = dev->dev_private;
>  
> -	if (pfdev->shrinker.nr_deferred) {
> -		unregister_shrinker(&pfdev->shrinker);
> -	}
> +	if (pfdev->shrinker)
> +		shrinker_unregister(pfdev->shrinker);
>  }