Re: [PATCH 2/2] drm/panthor: Implement evicted status for GEM objects

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

On Mon, 20 Apr 2026 17:47:00 +0200
Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:

> For fdinfo to be able to fill its evicted counter with data, panthor
> needs to keep track of whether a GEM object has ever been reclaimed.
> Just checking whether the pages are resident isn't enough, as newly
> allocated objects also won't be resident.
> 
> Do this with a new atomic_t member on panthor_gem_object. It's increased
> when an object gets evicted by the shrinker. While it's allowed to wrap
> around to below zero and assume a value less than a previous observed
> value, the reclaim counter will never return to 0 for any particular
> object once it's been reclaimed at least once.
> 
> Use this new member to then set the appropriate DRM_GEM_OBJECT_EVICTED
> status flag for fdinfo, and use it in the gems debugfs. It's possible to
> distinguish evicted non-resident pages from newly allocated non-resident
> pages by checking whether reclaimed_count is != 0.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 10 ++++++++++
>  drivers/gpu/drm/panthor/panthor_gem.h | 11 +++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 69cef05b6ef7..4b761b39565d 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -687,6 +687,10 @@ static void panthor_gem_evict_locked(struct panthor_gem_object *bo)
>  	if (drm_WARN_ON_ONCE(bo->base.dev, !bo->backing.pages))
>  		return;
>  
> +	/* Don't ever wrap around as far as 0, jump from INT_MIN to 1 */
> +	if (!atomic_inc_unless_negative(&bo->reclaimed_count))
> +		atomic_set(&bo->reclaimed_count, 1);

Can't we just go

	atomic_add_unless(&bo->reclaimed_count, 1, INT_MAX);

here, to handle the INT_MAX saturation?

> +
>  	panthor_gem_dev_map_cleanup_locked(bo);
>  	panthor_gem_backing_cleanup_locked(bo);
>  	panthor_gem_update_reclaim_state_locked(bo, NULL);
> @@ -788,6 +792,8 @@ static enum drm_gem_object_status panthor_gem_status(struct drm_gem_object *obj)
>  
>  	if (drm_gem_is_imported(&bo->base) || bo->backing.pages)
>  		res |= DRM_GEM_OBJECT_RESIDENT;
> +	else if (atomic_read(&bo->reclaimed_count))
> +		res |= DRM_GEM_OBJECT_EVICTED;
>  
>  	return res;
>  }
> @@ -1595,6 +1601,7 @@ static void panthor_gem_debugfs_print_flag_names(struct seq_file *m)
>  	static const char * const gem_state_flags_names[] = {
>  		[PANTHOR_DEBUGFS_GEM_STATE_IMPORTED_BIT] = "imported",
>  		[PANTHOR_DEBUGFS_GEM_STATE_EXPORTED_BIT] = "exported",
> +		[PANTHOR_DEBUGFS_GEM_STATE_EVICTED_BIT] = "evicted",
>  	};
>  
>  	static const char * const gem_usage_flags_names[] = {
> @@ -1648,6 +1655,9 @@ static void panthor_gem_debugfs_bo_print(struct panthor_gem_object *bo,
>  
>  	if (drm_gem_is_imported(&bo->base))
>  		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_IMPORTED;
> +	else if (!resident_size && atomic_read(&bo->reclaimed_count))
> +		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_EVICTED;

I think it'd be interesting to know the number of times a BO got
evicted.

> +
>  	if (bo->base.dma_buf)
>  		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_EXPORTED;
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index ae0491d0b121..1ab573f03330 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.h
> +++ b/drivers/gpu/drm/panthor/panthor_gem.h
> @@ -19,12 +19,16 @@ struct panthor_vm;
>  enum panthor_debugfs_gem_state_flags {
>  	PANTHOR_DEBUGFS_GEM_STATE_IMPORTED_BIT = 0,
>  	PANTHOR_DEBUGFS_GEM_STATE_EXPORTED_BIT = 1,
> +	PANTHOR_DEBUGFS_GEM_STATE_EVICTED_BIT = 2,
>  
>  	/** @PANTHOR_DEBUGFS_GEM_STATE_FLAG_IMPORTED: GEM BO is PRIME imported. */
>  	PANTHOR_DEBUGFS_GEM_STATE_FLAG_IMPORTED = BIT(PANTHOR_DEBUGFS_GEM_STATE_IMPORTED_BIT),
>  
>  	/** @PANTHOR_DEBUGFS_GEM_STATE_FLAG_EXPORTED: GEM BO is PRIME exported. */
>  	PANTHOR_DEBUGFS_GEM_STATE_FLAG_EXPORTED = BIT(PANTHOR_DEBUGFS_GEM_STATE_EXPORTED_BIT),
> +
> +	/** @PANTHOR_DEBUGFS_GEM_STATE_FLAG_EVICTED: GEM BO is evicted to swap. */
> +	PANTHOR_DEBUGFS_GEM_STATE_FLAG_EVICTED = BIT(PANTHOR_DEBUGFS_GEM_STATE_EVICTED_BIT),
>  };
>  
>  enum panthor_debugfs_gem_usage_flags {
> @@ -172,6 +176,13 @@ struct panthor_gem_object {
>  	/** @reclaim_state: Cached reclaim state */
>  	enum panthor_gem_reclaim_state reclaim_state;
>  
> +	/**
> +	 * @reclaimed_count: How many times object has been evicted to swap.

	 *

> +	 * Never returns to 0 once incremented even on wrap-around, but may
> +	 * become < 0 and < the previous value if wrap-around occurs.

With the saturation I suggested, I'd just add that when INT_MAX is
reached, it will stay there.

> +	 */
> +	atomic_t reclaimed_count;
> +
>  	/**
>  	 * @exclusive_vm_root_gem: Root GEM of the exclusive VM this GEM object
>  	 * is attached to.
>