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

[Nicolas Frattaroli]

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

-- 
2.53.0