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

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Reporting per-order free block counts in drm_buddy_print() currently
requires walking all rbtrees, which is O(n) over the total number of
free blocks and holds the allocator lock for the duration. This becomes
expensive on large VRAM heaps with many small free fragments.

Maintain a free_scoreboard[] array indexed by order instead, so that
the count for any order is always available in O(1). The scoreboard is
kept accurate by hooking into the four places where a block's free state
changes: mark_free(), mark_allocated(), mark_split(), and the sites in
__gpu_buddy_free(), __force_merge(), and the four err_undo paths that
call rbtree_remove() directly on free blocks without going through
mark_*().

The print functions are simplified as a result: the rbtree traversal
is replaced by a direct array lookup.

v3: Update after introducing __gpu_buddy_undo_splits() helper

v2: Update after fix for use-after-free in split_block() call sites

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20260522092600.32818-5-francois.dugast@intel.com
Signed-off-by: Francois Dugast <francois.dugast@intel.com>

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This commit is contained in:

Francois Dugast 2026-05-22 11:25:31 +02:00

parent e16ac0132f

commit a03721ee48

3 changed files with 30 additions and 29 deletions

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36

drivers/gpu/buddy.c

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16

drivers/gpu/drm/drm_buddy.c

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7

include/linux/gpu_buddy.h

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