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

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

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@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.
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);
> >   }