Re: [PATCH v4 2/3] drm/panthor: Implement evicted status for GEM objects

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

On Wed, 20 May 2026 15:04:49 +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, and saturates at INT_MAX.
> This means that once an object has been evicted at least once, its
> reclaim counter will never return to 0.
> 
> Due to this, it's possible to distinguish evicted non-resident pages
> from newly allocated non-resident pages by checking whether
> reclaimed_count is != 0
> 
> Use this new member to then set the appropriate DRM_GEM_OBJECT_EVICTED
> status flag for fdinfo.
> 
> Also add a new column and status flag to the panthor gems debugfs: the
> column is the number of times an object has been evicted, whereas the
> flag indicates whether it currently is evicted.
> 
> Reviewed-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

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

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 18 ++++++++++++++----
>  drivers/gpu/drm/panthor/panthor_gem.h | 10 ++++++++++
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index 13295d7a593d..068aa935c8fc 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -687,6 +687,8 @@ static void panthor_gem_evict_locked(struct panthor_gem_object *bo)
>  	if (drm_WARN_ON_ONCE(bo->base.dev, !bo->backing.pages))
>  		return;
>  
> +	atomic_add_unless(&bo->reclaimed_count, 1, INT_MAX);
> +
>  	panthor_gem_dev_map_cleanup_locked(bo);
>  	panthor_gem_backing_cleanup_locked(bo);
>  	panthor_gem_update_reclaim_state_locked(bo, NULL);
> @@ -788,6 +790,8 @@ 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 +1599,7 @@ 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[] = {
> @@ -1625,6 +1630,7 @@ static void panthor_gem_debugfs_bo_print(struct panthor_gem_object *bo,
>  {
>  	enum panthor_gem_reclaim_state reclaim_state = bo->reclaim_state;
>  	unsigned int refcount = kref_read(&bo->base.refcount);
> +	int reclaimed_count = atomic_read(&bo->reclaimed_count);
>  	char creator_info[32] = {};
>  	size_t resident_size;
>  	u32 gem_usage_flags = bo->debugfs.flags;
> @@ -1638,16 +1644,20 @@ static void panthor_gem_debugfs_bo_print(struct panthor_gem_object *bo,
>  
>  	snprintf(creator_info, sizeof(creator_info),
>  		 "%s/%d", bo->debugfs.creator.process_name, bo->debugfs.creator.tgid);
> -	seq_printf(m, "%-32s%-16d%-16d%-16zd%-16zd0x%-16lx",
> +	seq_printf(m, "%-32s%-16d%-16d%-11d%-16zd%-16zd0x%-16lx",
>  		   creator_info,
>  		   bo->base.name,
>  		   refcount,
> +		   reclaimed_count,
>  		   bo->base.size,
>  		   resident_size,
>  		   drm_vma_node_start(&bo->base.vma_node));
>  
>  	if (drm_gem_is_imported(&bo->base))
>  		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_IMPORTED;
> +	else if (!resident_size && reclaimed_count)
> +		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_EVICTED;
> +
>  	if (bo->base.dma_buf)
>  		gem_state_flags |= PANTHOR_DEBUGFS_GEM_STATE_FLAG_EXPORTED;
>  
> @@ -1671,8 +1681,8 @@ static void panthor_gem_debugfs_print_bos(struct panthor_device *ptdev,
>  
>  	panthor_gem_debugfs_print_flag_names(m);
>  
> -	seq_puts(m, "created-by                      global-name     refcount        size            resident-size   file-offset       state      usage       label\n");
> -	seq_puts(m, "----------------------------------------------------------------------------------------------------------------------------------------------\n");
> +	seq_puts(m, "created-by                      global-name     refcount        evictions  size            resident-size   file-offset       state      usage       label\n");
> +	seq_puts(m, "---------------------------------------------------------------------------------------------------------------------------------------------------------\n");
>  
>  	scoped_guard(mutex, &ptdev->gems.lock) {
>  		list_for_each_entry(bo, &ptdev->gems.node, debugfs.node) {
> @@ -1680,7 +1690,7 @@ static void panthor_gem_debugfs_print_bos(struct panthor_device *ptdev,
>  		}
>  	}
>  
> -	seq_puts(m, "==============================================================================================================================================\n");
> +	seq_puts(m, "=========================================================================================================================================================\n");
>  	seq_printf(m, "Total size: %zd, Total resident: %zd, Total reclaimable: %zd\n",
>  		   totals.size, totals.resident, totals.reclaimable);
>  }
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.h b/drivers/gpu/drm/panthor/panthor_gem.h
> index ae0491d0b121..56d63137b4eb 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 +176,12 @@ 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.
> +	 * The count saturates at %INT_MAX and will never wrap around to 0.
> +	 */
> +	atomic_t reclaimed_count;
> +
>  	/**
>  	 * @exclusive_vm_root_gem: Root GEM of the exclusive VM this GEM object
>  	 * is attached to.
>