drm/gem: Add LRU/shrinker helper

Add a simple LRU helper to assist with driver's shrinker implementation.
It handles tracking the number of backing pages associated with a given
LRU, and provides a helper to implement shrinker_scan.

A driver can use multiple LRU instances to track objects in various
states, for example a dontneed LRU for purgeable objects, a willneed LRU
for evictable objects, and an unpinned LRU for objects without backing
pages.

All LRUs that the object can be moved between must share a single lock.

v2: lockdep_assert_held() instead of WARN_ON(!mutex_is_locked())
v3: make drm_gem_lru_move_tail_locked() static until there is a user

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Patchwork: https://patchwork.freedesktop.org/patch/496128/
Link: https://lore.kernel.org/r/20220802155152.1727594-10-robdclark@gmail.com

1 files changed, 55 insertions, 0 deletions

diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index 87cffc9efa85..f28a48a6f846 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -175,6 +175,41 @@ struct drm_gem_object_funcs {
 };
 
 /**
+ * struct drm_gem_lru - A simple LRU helper
+ *
+ * A helper for tracking GEM objects in a given state, to aid in
+ * driver's shrinker implementation.  Tracks the count of pages
+ * for lockless &shrinker.count_objects, and provides
+ * &drm_gem_lru_scan for driver's &shrinker.scan_objects
+ * implementation.
+ */
+struct drm_gem_lru {
+	/**
+	 * @lock:
+	 *
+	 * Lock protecting movement of GEM objects between LRUs.  All
+	 * LRUs that the object can move between should be protected
+	 * by the same lock.
+	 */
+	struct mutex *lock;
+
+	/**
+	 * @count:
+	 *
+	 * The total number of backing pages of the GEM objects in
+	 * this LRU.
+	 */
+	long count;
+
+	/**
+	 * @list:
+	 *
+	 * The LRU list.
+	 */
+	struct list_head list;
+};
+
+/**
  * struct drm_gem_object - GEM buffer object
  *
  * This structure defines the generic parts for GEM buffer objects, which are
@@ -312,6 +347,20 @@ struct drm_gem_object {
 	 *
 	 */
 	const struct drm_gem_object_funcs *funcs;
+
+	/**
+	 * @lru_node:
+	 *
+	 * List node in a &drm_gem_lru.
+	 */
+	struct list_head lru_node;
+
+	/**
+	 * @lru:
+	 *
+	 * The current LRU list that the GEM object is on.
+	 */
+	struct drm_gem_lru *lru;
 };
 
 /**
@@ -420,4 +469,10 @@ void drm_gem_unlock_reservations(struct drm_gem_object **objs, int count,
 int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
 			    u32 handle, u64 *offset);
 
+void drm_gem_lru_init(struct drm_gem_lru *lru, struct mutex *lock);
+void drm_gem_lru_remove(struct drm_gem_object *obj);
+void drm_gem_lru_move_tail(struct drm_gem_lru *lru, struct drm_gem_object *obj);
+unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
+			       bool (*shrink)(struct drm_gem_object *obj));
+
 #endif /* __DRM_GEM_H__ */