Subject: Re: [PATCH v2 23/47] drm/msm: dynamically allocate the drm-msm_gem shrinker

From: Muchun Song <[email-masked]>
Date: Wed, 26 Jul 2023 15:24:02 +0800

On 2023/7/24 17:43, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the drm-msm_gem 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 msm_drm_private.
>
> Signed-off-by: Qi Zheng <[email-masked]>

Reviewed-by: Muchun Song <[email-masked]>

A nit bellow.

> ---
>   drivers/gpu/drm/msm/msm_drv.c          |  4 ++-
>   drivers/gpu/drm/msm/msm_drv.h          |  4 +--
>   drivers/gpu/drm/msm/msm_gem_shrinker.c | 36 ++++++++++++++++----------
>   3 files changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 891eff8433a9..7f6933be703f 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -461,7 +461,9 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)
>   	if (ret)
>   		goto err_msm_uninit;
>   
> -	msm_gem_shrinker_init(ddev);
> +	ret = msm_gem_shrinker_init(ddev);
> +	if (ret)
> +		goto err_msm_uninit;
>   
>   	if (priv->kms_init) {
>   		ret = priv->kms_init(ddev);
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index e13a8cbd61c9..84523d4a1e58 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -217,7 +217,7 @@ struct msm_drm_private {
>   	} vram;
>   
>   	struct notifier_block vmap_notifier;
> -	struct shrinker shrinker;
> +	struct shrinker *shrinker;
>   
>   	struct drm_atomic_state *pm_state;
>   
> @@ -279,7 +279,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>   unsigned long msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan);
>   #endif
>   
> -void msm_gem_shrinker_init(struct drm_device *dev);
> +int msm_gem_shrinker_init(struct drm_device *dev);
>   void msm_gem_shrinker_cleanup(struct drm_device *dev);
>   
>   int msm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
> diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> index f38296ad8743..7daab1298c11 100644
> --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> @@ -34,8 +34,7 @@ static bool can_block(struct shrink_control *sc)
>   static unsigned long
>   msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
>   {
> -	struct msm_drm_private *priv =
> -		container_of(shrinker, struct msm_drm_private, shrinker);
> +	struct msm_drm_private *priv = shrinker->private_data;
>   	unsigned count = priv->lru.dontneed.count;
>   
>   	if (can_swap())
> @@ -100,8 +99,7 @@ active_evict(struct drm_gem_object *obj)
>   static unsigned long
>   msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>   {
> -	struct msm_drm_private *priv =
> -		container_of(shrinker, struct msm_drm_private, shrinker);
> +	struct msm_drm_private *priv = shrinker->private_data;
>   	struct {
>   		struct drm_gem_lru *lru;
>   		bool (*shrink)(struct drm_gem_object *obj);
> @@ -148,10 +146,11 @@ msm_gem_shrinker_shrink(struct drm_device *dev, unsigned long nr_to_scan)
>   	struct shrink_control sc = {
>   		.nr_to_scan = nr_to_scan,
>   	};
> -	int ret;
> +	unsigned long ret = SHRINK_STOP;
>   
>   	fs_reclaim_acquire(GFP_KERNEL);
> -	ret = msm_gem_shrinker_scan(&priv->shrinker, &sc);
> +	if (priv->shrinker)
> +		ret = msm_gem_shrinker_scan(priv->shrinker, &sc);
>   	fs_reclaim_release(GFP_KERNEL);
>   
>   	return ret;
> @@ -210,16 +209,27 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
>    *
>    * This function registers and sets up the msm shrinker.
>    */
> -void msm_gem_shrinker_init(struct drm_device *dev)
> +int msm_gem_shrinker_init(struct drm_device *dev)
>   {
>   	struct msm_drm_private *priv = dev->dev_private;
> -	priv->shrinker.count_objects = msm_gem_shrinker_count;
> -	priv->shrinker.scan_objects = msm_gem_shrinker_scan;
> -	priv->shrinker.seeks = DEFAULT_SEEKS;
> -	WARN_ON(register_shrinker(&priv->shrinker, "drm-msm_gem"));
> +
> +	priv->shrinker = shrinker_alloc(0, "drm-msm_gem");
> +	if (!priv->shrinker) {

Just "if (WARN_ON(!priv->shrinker))"

> +		WARN_ON(1);
> +		return -ENOMEM;
> +	}
> +
> +	priv->shrinker->count_objects = msm_gem_shrinker_count;
> +	priv->shrinker->scan_objects = msm_gem_shrinker_scan;
> +	priv->shrinker->seeks = DEFAULT_SEEKS;
> +	priv->shrinker->private_data = priv;
> +
> +	shrinker_register(priv->shrinker);
>   
>   	priv->vmap_notifier.notifier_call = msm_gem_shrinker_vmap;
>   	WARN_ON(register_vmap_purge_notifier(&priv->vmap_notifier));
> +
> +	return 0;
>   }
>   
>   /**
> @@ -232,8 +242,8 @@ void msm_gem_shrinker_cleanup(struct drm_device *dev)
>   {
>   	struct msm_drm_private *priv = dev->dev_private;
>   
> -	if (priv->shrinker.nr_deferred) {
> +	if (priv->shrinker) {
>   		WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
> -		unregister_shrinker(&priv->shrinker);
> +		shrinker_unregister(priv->shrinker);
>   	}
>   }