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

[Qi Zheng <zhengqi.arch@bytedance.com>]

On 2023/7/26 15:24, Muchun Song wrote:
> 
> 
> 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 <zhengqi.arch@bytedance.com>
> 
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> 
> 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))"

As suggested by Steven Pric in patch #24, this warning is
unnecessary, so I will remove it in the next version.

> 
>> +        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);
>>       }
>>   }
>