Re: [PATCH v2 3/6] drm/panfrost: Add fdinfo support for memory stats

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 24 Aug 2023 02:34:46 +0100
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> A new DRM GEM object function is added so that drm_show_memory_stats can
> provider more accurate memory usage numbers.

  s/provider/provide/

> 
> Ideally, in panfrost_gem_status, the BO's purgeable flag would be checked
> after locking the driver's shrinker mutex, but drm_show_memory_stats takes
> over the drm file's object handle database spinlock, so there's potential
> for a race condition here.

Yeah, I don't think it matters much if we report a BO non-purgeable,
and this BO becomes purgeable in the meantime. You'd have the same
problem

> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> ---
>  drivers/gpu/drm/panfrost/panfrost_drv.c |  9 +++++++--
>  drivers/gpu/drm/panfrost/panfrost_gem.c | 12 ++++++++++++
>  drivers/gpu/drm/panfrost/panfrost_gem.h |  1 +
>  3 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> index 3fd372301019..93d5f5538c0b 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> @@ -440,11 +440,14 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
>  	args->retained = drm_gem_shmem_madvise(&bo->base, args->madv);
>  
>  	if (args->retained) {
> -		if (args->madv == PANFROST_MADV_DONTNEED)
> +		if (args->madv == PANFROST_MADV_DONTNEED) {
>  			list_move_tail(&bo->base.madv_list,
>  				       &pfdev->shrinker_list);
> -		else if (args->madv == PANFROST_MADV_WILLNEED)
> +			bo->is_purgable = true;
> +		} else if (args->madv == PANFROST_MADV_WILLNEED) {
>  			list_del_init(&bo->base.madv_list);
> +			bo->is_purgable = false;

Should we really flag the BO as purgeable if it's already been evicted
(args->retained == false)?

> +		}
>  	}
>  
>  out_unlock_mappings:
> @@ -559,6 +562,8 @@ static void panfrost_show_fdinfo(struct drm_printer *p, struct drm_file *file)
>  	struct panfrost_device *pfdev = dev->dev_private;
>  
>  	panfrost_gpu_show_fdinfo(pfdev, file->driver_priv, p);
> +
> +	drm_show_memory_stats(p, file);
>  }
>  
>  static const struct file_operations panfrost_drm_driver_fops = {
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
> index 3c812fbd126f..aea16b0e4dda 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
> @@ -195,6 +195,17 @@ static int panfrost_gem_pin(struct drm_gem_object *obj)
>  	return drm_gem_shmem_pin(&bo->base);
>  }
>  
> +static enum drm_gem_object_status panfrost_gem_status(struct drm_gem_object *obj)
> +{
> +	struct panfrost_gem_object *bo = to_panfrost_bo(obj);
> +	enum drm_gem_object_status res = 0;
> +
> +	res |= (bo->is_purgable) ? DRM_GEM_OBJECT_PURGEABLE : 0;

Why not checking bo->base.madv here instead of adding an is_purgeable
field?

> +
> +	res |= (bo->base.pages) ? DRM_GEM_OBJECT_RESIDENT : 0;

Does it make sense to have DRM_GEM_OBJECT_PURGEABLE set when
DRM_GEM_OBJECT_RESIDENT is not?

> +
> +	return res;
> +}
>  static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>  	.free = panfrost_gem_free_object,
>  	.open = panfrost_gem_open,
> @@ -206,6 +217,7 @@ static const struct drm_gem_object_funcs panfrost_gem_funcs = {
>  	.vmap = drm_gem_shmem_object_vmap,
>  	.vunmap = drm_gem_shmem_object_vunmap,
>  	.mmap = drm_gem_shmem_object_mmap,
> +	.status = panfrost_gem_status,
>  	.vm_ops = &drm_gem_shmem_vm_ops,
>  };
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> index ad2877eeeccd..e06f7ceb8f73 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> @@ -38,6 +38,7 @@ struct panfrost_gem_object {
>  
>  	bool noexec		:1;
>  	bool is_heap		:1;
> +	bool is_purgable	:1;
>  };
>  
>  struct panfrost_gem_mapping {