Re: [PATCH 2/2] gpu/buddy: Track per-order used blocks with a scoreboard

Fri, 08 May 2026 07:13:15 -0700 

On 04/05/2026 14:52, Francois Dugast wrote:

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().

Signed-off-by: Francois Dugast <[email protected]>
Assisted-by: GitHub Copilot:claude-sonnet-4.6


Reviewed-by: Matthew Auld <[email protected]>
Note that Sashiko found an existing issue here: https://sashiko.dev/#/patchset/20260504135343.1797869-1-francois.dugast%40intel.com 

I guess would be good to fix that first, in this series?


---
  drivers/gpu/buddy.c         | 29 +++++++++++++++++++++++------
  drivers/gpu/drm/drm_buddy.c |  8 +++++---
  include/linux/gpu_buddy.h   |  8 ++++++++
  3 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
index d831165e87ea..ebef03613b3f 100644
--- a/drivers/gpu/buddy.c
+++ b/drivers/gpu/buddy.c
@@ -194,6 +194,7 @@ static void mark_allocated(struct gpu_buddy *mm,
        block->header |= GPU_BUDDY_ALLOCATED;
mm->free_scoreboard[gpu_buddy_block_order(block)]--; 
+       mm->used_scoreboard[gpu_buddy_block_order(block)]++;
rbtree_remove(mm, block); 
  }
@@ -203,6 +204,9 @@ static void mark_free(struct gpu_buddy *mm,
  {
        enum gpu_buddy_free_tree tree;
+ if (gpu_buddy_block_is_allocated(block)) 
+               mm->used_scoreboard[gpu_buddy_block_order(block)]--;
+
        block->header &= ~GPU_BUDDY_HEADER_STATE;
        block->header |= GPU_BUDDY_FREE;
@@ -281,6 +285,9 @@ static unsigned int __gpu_buddy_free(struct gpu_buddy *mm, 
                if (force_merge && gpu_buddy_block_is_clear(buddy))
                        mm->clear_avail -= gpu_buddy_block_size(mm, buddy);
+ if (gpu_buddy_block_is_allocated(block)) 
+                       mm->used_scoreboard[gpu_buddy_block_order(block)]--;
+
                gpu_block_free(mm, block);
                gpu_block_free(mm, buddy);
@@ -398,6 +405,12 @@ int gpu_buddy_init(struct gpu_buddy *mm, u64 size, u64 chunk_size) 
        if (!mm->free_scoreboard)
                return -ENOMEM;
+ mm->used_scoreboard = kcalloc(mm->max_order + 1, 
+                                     sizeof(*mm->used_scoreboard),
+                                     GFP_KERNEL);
+       if (!mm->used_scoreboard)
+               goto out_free_free_scoreboard;
+
        mm->free_trees = kmalloc_array(GPU_BUDDY_MAX_FREE_TREES,
                                       sizeof(*mm->free_trees),
                                       GFP_KERNEL);
@@ -462,6 +475,8 @@ int gpu_buddy_init(struct gpu_buddy *mm, u64 size, u64 
chunk_size)
                kfree(mm->free_trees[i]);
        kfree(mm->free_trees);
  out_free_scoreboard:
+       kfree(mm->used_scoreboard);
+out_free_free_scoreboard:
        kfree(mm->free_scoreboard);
        return -ENOMEM;
  }
@@ -502,6 +517,7 @@ void gpu_buddy_fini(struct gpu_buddy *mm)
        kfree(mm->free_trees);
        kfree(mm->roots);
        kfree(mm->free_scoreboard);
+       kfree(mm->used_scoreboard);
  }
  EXPORT_SYMBOL(gpu_buddy_fini);
@@ -1496,15 +1512,16 @@ void gpu_buddy_print(struct gpu_buddy *mm) 
                mm->chunk_size >> 10, mm->size >> 20, mm->avail >> 20, 
mm->clear_avail >> 20);
for (order = mm->max_order; order >= 0; order--) { 
-               u64 count = mm->free_scoreboard[order];
-               u64 free = count * (mm->chunk_size << order);
+               u64 free_count = mm->free_scoreboard[order];
+               u64 used_count = mm->used_scoreboard[order];
+               u64 free = free_count * (mm->chunk_size << order);
if (free < SZ_1M) 
-                       pr_info("order-%2d free: %8llu KiB, blocks: %llu\n",
-                               order, free >> 10, count);
+                       pr_info("order-%2d free: %8llu KiB, free_blocks: %llu, 
used_blocks: %llu\n",
+                               order, free >> 10, free_count, used_count);
                else
-                       pr_info("order-%2d free: %8llu MiB, blocks: %llu\n",
-                               order, free >> 20, count);
+                       pr_info("order-%2d free: %8llu MiB, free_blocks: %llu, 
used_blocks: %llu\n",
+                               order, free >> 20, free_count, used_count);
        }
  }
  EXPORT_SYMBOL(gpu_buddy_print);
diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 7839b54d3da7..3a1cb06923c6 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -46,8 +46,9 @@ void drm_buddy_print(struct gpu_buddy *mm, struct drm_printer 
*p)
                   mm->chunk_size >> 10, mm->size >> 20, mm->avail >> 20, 
mm->clear_avail >> 20);
for (order = mm->max_order; order >= 0; order--) { 
-               u64 count = mm->free_scoreboard[order];
-               u64 free = count * (mm->chunk_size << order);
+               u64 free_count = mm->free_scoreboard[order];
+               u64 used_count = mm->used_scoreboard[order];
+               u64 free = free_count * (mm->chunk_size << order);
drm_printf(p, "order-%2d ", order); @@ -56,7 +57,8 @@ void drm_buddy_print(struct gpu_buddy *mm, struct drm_printer *p) 
                else
                        drm_printf(p, "free: %8llu MiB", free >> 20);
- drm_printf(p, ", blocks: %llu\n", count); 
+               drm_printf(p, ", free_blocks: %llu, used_blocks: %llu\n",
+                          free_count, used_count);
        }
  }
  EXPORT_SYMBOL(drm_buddy_print);
diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
index 250841ca4bcf..b1cad7833dc1 100644
--- a/include/linux/gpu_buddy.h
+++ b/include/linux/gpu_buddy.h
@@ -179,6 +179,14 @@ struct gpu_buddy {
         * mark_split() when a block leaves the free state.
         */
        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
+        * gpu_buddy_free_block() which is the sole entry point for freeing
+        * allocated blocks.
+        */
+       u64 *used_scoreboard;
  /* public: */
        unsigned int n_roots;
        unsigned int max_order;

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