gpu/buddy: Track per-order used blocks with a scoreboard

Extend the scoreboard approach from the previous commit to used blocks,
so drm_buddy_print() can report per-order allocation pressure in O(1).

Unlike free blocks, an allocated block can leave the allocated state
through mark_free() (normal free and gpu_buddy_block_trim()) or be
consumed directly by gpu_block_free() during coalescing. Both sites are
guarded by gpu_buddy_block_is_allocated() and paired with the increment
in mark_allocated().

v3:
- Assert scoreboard is empty at fini(), as sanity check (Matthew Auld)

v2:
- Update after fix for use-after-free in split_block() call sites
- Change goto label to out_free_used_scoreboard for clarity
- Make drm_buddy_print() and gpu_buddy_print() symmetric for used and
  free

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20260522092600.32818-6-francois.dugast@intel.com
Signed-off-by: Francois Dugast <francois.dugast@intel.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
index a28f7d7637ca..e037714563d8 100644
--- a/include/linux/gpu_buddy.h
+++ b/include/linux/gpu_buddy.h
@@ -180,6 +180,14 @@ struct gpu_buddy {
 	 * called on a free block.
 	 */
 	u64 *free_scoreboard;
+	/*
+	 * Per-order used block scoreboard: used_scoreboard[order] holds the
+	 * number of blocks of that order currently in the allocated state.
+	 * Incremented in mark_allocated(), decremented in mark_free() (guarded
+	 * by gpu_buddy_block_is_allocated()) and in __gpu_buddy_free() when an
+	 * allocated block is consumed directly during buddy coalescing.
+	 */
+	u64 *used_scoreboard;
 /* public: */
 	unsigned int n_roots;
 	unsigned int max_order;