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

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Message-ID: <6049aa99-aa47-5137-f66e-350bc4723914@bytedance.com>
Date: Tue, 25 Jul 2023 11:05:04 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Steven Price <steven.price@....com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
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Subject: Re: [PATCH v2 24/47] drm/panfrost: dynamically allocate the
 drm-panfrost shrinker

Hi Steven,

On 2023/7/24 19:17, Steven Price wrote:
> 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@...edance.com>
> 
> One nit below, but otherwise:
> 
> Reviewed-by: Steven Price <steven.price@....com>
> 
>> ---
>>   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.

Make sense. Will delete this WARN_ON() in the next version.

Thanks,
Qi

> 
>> +		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);
>>   }
>