Re: [PATCH v2 4/6] drm/drm_file: Add DRM obj's RSS reporting function for fdinfo

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

On Thu, 24 Aug 2023 02:34:47 +0100
Adrián Larumbe <adrian.larumbe@collabora.com> wrote:

> Some BO's might be mapped onto physical memory chunkwise and on demand,
> like Panfrost's tiler heap. In this case, even though the
> drm_gem_shmem_object page array might already be allocated, only a very
> small fraction of the BO is currently backed by system memory, but
> drm_show_memory_stats will then proceed to add its entire virtual size to
> the file's total resident size regardless.
> 
> This led to very unrealistic RSS sizes being reckoned for Panfrost, where
> said tiler heap buffer is initially allocated with a virtual size of 128
> MiB, but only a small part of it will eventually be backed by system memory
> after successive GPU page faults.
> 
> Provide a new DRM object generic function that would allow drivers to
> return a more accurate RSS size for their BOs.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/drm_file.c | 5 ++++-
>  include/drm/drm_gem.h      | 9 +++++++++
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 883d83bc0e3d..762965e3d503 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -944,7 +944,10 @@ void drm_show_memory_stats(struct drm_printer *p, struct drm_file *file)
>  		}
>  
>  		if (s & DRM_GEM_OBJECT_RESIDENT) {
> -			status.resident += obj->size;
> +			if (obj->funcs && obj->funcs->rss)
> +				status.resident += obj->funcs->rss(obj);
> +			else
> +				status.resident += obj->size;
>  		} else {
>  			/* If already purged or not yet backed by pages, don't
>  			 * count it as purgeable:
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index c0b13c43b459..78ed9fab6044 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -208,6 +208,15 @@ struct drm_gem_object_funcs {
>  	 */
>  	enum drm_gem_object_status (*status)(struct drm_gem_object *obj);
>  
> +	/**
> +	 * @rss:
> +	 *
> +	 * Return resident size of the object in physical memory.
> +	 *
> +	 * Called by drm_show_memory_stats().
> +	 */
> +	size_t (*rss)(struct drm_gem_object *obj);
> +
>  	/**
>  	 * @vm_ops:
>  	 *