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* [PATCH v3] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation
@ 2026-11-03 12:56 Arunpravin Paneer Selvam
  2026-11-03 13:09 ` sashiko-bot
                   ` (6 more replies)
  0 siblings, 7 replies; 8+ messages in thread
From: Arunpravin Paneer Selvam @ 2026-11-03 12:56 UTC (permalink / raw)
  To: matthew.auld, dri-devel, intel-gfx, intel-xe, amd-gfx
  Cc: christian.koenig, alexander.deucher, Anand.Raghavendra,
	Arunpravin Paneer Selvam

From: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>

Range-restricted allocations (the visible-VRAM aperture) skip
dirty_steer_window() and reach __alloc_range_bias() with no clear/dirty
eligibility guard, so a dirty allocation freely splits clear extents (and
vice versa), interleaving the two classes until no large same-class run
survives and a 4K scanout pin fails with -ENOSPC. Use a two-pass range
search instead: block_incompatible() rejects opposite-class blocks in the
strict pass and relaxes only when the strict pass returns -ENOSPC, so a
request still succeeds when only opposite-class space remains. A KUnit
regression test covers the interleaving pattern and fails without the
guard.

v2: the strict pass can split a block and then reject both children, so
    a split no longer implies a compatible block exists. Sashiko reported
    the resulting leaked splits; fix as suggested by Matthew:
 - Push the parent back on the DFS stack after each split and merge it
   back with unsplit_block() if both children are still free.
 - Make block_incompatible() judge free blocks only (split nodes keep a
   stale clear bit) and take the requested order, so mixed blocks that
   can hold a compatible block are descended instead of skipped.
 - Extend the KUnit test with a coalesced mixed block and a check that
   a rejected split is merged back.

v3: igt@kms_plane@plane-panning-bottom-right failed on Radeon RX 9070 XT
    with -ENOSPC: the range allocator's strict pass split mixed blocks to
    look for a wholly-clear (or wholly-dirty) leaf, discarded the mixed
    leaves it found, and ran unsplit_block to merge the splits back, whose
    per-allocation cost and residual fragmentation starved the large
    pipe-A scanout. Fix: accept a mixed block at the requested order as-is
    (caller re-clears), so the first pass no longer splits and discards
    mixed blocks. This clear/dirty compatibility relaxation applies only
    to range-biased allocation, where keeping blocks intact reduces
    fragmentation and preserves large contiguous spaces. The now-unneeded
    unsplit_block helper is dropped.

Fixes: 1ad5e807f716 ("gpu/buddy: replace dual-tree/force_merge with decoupled dirty tracker")
Assisted-by: LLM
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
---
 drivers/gpu/buddy.c                | 75 +++++++++++++-------------
 drivers/gpu/tests/gpu_buddy_test.c | 84 ++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
index 28cff97d57dc..f2914f919b04 100644
--- a/drivers/gpu/buddy.c
+++ b/drivers/gpu/buddy.c
@@ -1240,11 +1240,23 @@ static void __gpu_buddy_undo_splits(struct gpu_buddy *mm,
 	}
 }
 
+static bool block_incompatible(struct gpu_buddy_block *block, unsigned int flags)
+{
+	bool needs_clear = flags & GPU_BUDDY_CLEAR_ALLOCATION;
+
+	if (!gpu_buddy_block_is_free(block))
+		return false;
+
+	return needs_clear ? !block->has_clear :
+			     gpu_buddy_block_is_clear(block);
+}
+
 static struct gpu_buddy_block *
 __alloc_range_bias(struct gpu_buddy *mm,
 		   u64 start, u64 end,
 		   unsigned int order,
-		   unsigned long flags)
+		   unsigned long flags,
+		   bool fallback)
 {
 	u64 req_size = mm->chunk_size << order;
 	struct gpu_buddy_block *block;
@@ -1258,9 +1270,7 @@ __alloc_range_bias(struct gpu_buddy *mm,
 	 * This range-constrained search hands back the highest/right-most
 	 * address that satisfies the request: the roots are seeded high-to-low
 	 * and the right (higher-address) child is descended first, making
-	 * top-down the default placement here. A non-top-down clear request is
-	 * the only exception, where the descent is biased towards clear or
-	 * clear-containing subtrees to satisfy the clear preference.
+	 * top-down the default placement here.
 	 */
 	for (i = mm->n_roots - 1; i >= 0; --i)
 		list_add_tail(&mm->roots[i]->tmp_link, &dfs);
@@ -1298,6 +1308,9 @@ __alloc_range_bias(struct gpu_buddy *mm,
 				continue;
 		}
 
+		if (!fallback && block_incompatible(block, flags))
+			continue;
+
 		if (contains(start, end, block_start, block_end) &&
 		    order == gpu_buddy_block_order(block)) {
 			/*
@@ -1315,38 +1328,8 @@ __alloc_range_bias(struct gpu_buddy *mm,
 				goto err_undo;
 		}
 
-		/*
-		 * Top-down is a strict address-placement policy, so when it is
-		 * requested we ignore clear steering and simply descend the
-		 * right (higher-address) child first. Only a non-top-down clear
-		 * request biases the descent towards clear/has_clear subtrees.
-		 */
-		if ((flags & GPU_BUDDY_CLEAR_ALLOCATION) &&
-		    !(flags & GPU_BUDDY_TOPDOWN_ALLOCATION)) {
-			struct gpu_buddy_block *prefer;
-
-			if (gpu_buddy_block_is_clear(block->right))
-				prefer = block->right;
-			else if (gpu_buddy_block_is_clear(block->left))
-				prefer = block->left;
-			else if (block->right->has_clear)
-				prefer = block->right;
-			else if (block->left->has_clear)
-				prefer = block->left;
-			else
-				prefer = block->right;
-
-			if (prefer == block->right) {
-				list_add(&block->left->tmp_link, &dfs);
-				list_add(&block->right->tmp_link, &dfs);
-			} else {
-				list_add(&block->right->tmp_link, &dfs);
-				list_add(&block->left->tmp_link, &dfs);
-			}
-		} else {
-			list_add(&block->left->tmp_link, &dfs);
-			list_add(&block->right->tmp_link, &dfs);
-		}
+		list_add(&block->left->tmp_link, &dfs);
+		list_add(&block->right->tmp_link, &dfs);
 	} while (1);
 
 	return ERR_PTR(-ENOSPC);
@@ -1361,6 +1344,24 @@ __alloc_range_bias(struct gpu_buddy *mm,
 	return ERR_PTR(err);
 }
 
+static struct gpu_buddy_block *
+__gpu_buddy_alloc_range_bias(struct gpu_buddy *mm,
+			     u64 start, u64 end,
+			     unsigned int order,
+			     unsigned long flags)
+{
+	struct gpu_buddy_block *block;
+	bool fallback = false;
+
+	block = __alloc_range_bias(mm, start, end, order,
+				   flags, fallback);
+	if (IS_ERR(block))
+		return __alloc_range_bias(mm, start, end, order,
+					  flags, !fallback);
+
+	return block;
+}
+
 /* Return the highest-address free block of at least @order. */
 static struct gpu_buddy_block *
 get_maxblock(struct gpu_buddy *mm,
@@ -1924,7 +1925,7 @@ __gpu_buddy_alloc_blocks(struct gpu_buddy *mm,
 
 	if (flags & GPU_BUDDY_RANGE_ALLOCATION) {
 		/* Allocate traversing within the range */
-		block = __alloc_range_bias(mm, start, end, order, flags);
+		block = __gpu_buddy_alloc_range_bias(mm, start, end, order, flags);
 		if (!IS_ERR(block) || !steered)
 			return block;
 
diff --git a/drivers/gpu/tests/gpu_buddy_test.c b/drivers/gpu/tests/gpu_buddy_test.c
index 2c6f1da1a6d1..9aaca2fc6a02 100644
--- a/drivers/gpu/tests/gpu_buddy_test.c
+++ b/drivers/gpu/tests/gpu_buddy_test.c
@@ -1606,6 +1606,89 @@ static int gpu_buddy_suite_init(struct kunit_suite *suite)
 	return 0;
 }
 
+static void gpu_test_buddy_alloc_range_clear_guard(struct kunit *test)
+{
+	const unsigned long chunk = SZ_1M, mm_size = SZ_4M;
+	struct gpu_buddy_block *block;
+	LIST_HEAD(low_dirty);
+	LIST_HEAD(high_a);
+	LIST_HEAD(high_b);
+	LIST_HEAD(barrier);
+	LIST_HEAD(dirty_res);
+	LIST_HEAD(clear_res);
+	struct gpu_buddy mm;
+
+	KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_init(&mm, mm_size, chunk),
+			       "buddy_init failed\n");
+
+	/*
+	 * Idea is to lay out a range allocation as a low dirty block, an
+	 * allocated barrier, and a high naturally-aligned clear extent, then
+	 * issue a dirty range allocation. It must take the low dirty block and
+	 * leave the clear extent intact; if it instead cuts the clear extent,
+	 * a following same-class clear allocation can no longer find a
+	 * contiguous clear run and fails with -ENOSPC.
+	 *
+	 *   [0,  1M)   dirty free
+	 *   [1M, 2M)   allocated  (barrier, keeps the halves un-mergeable)
+	 *   [2M, 4M)   clear free (one naturally aligned 2 MiB extent)
+	 */
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 0, chunk, chunk, chunk,
+						      &low_dirty, GPU_BUDDY_RANGE_ALLOCATION),
+			       "alloc [0, 1M) failed\n");
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, chunk, 2 * chunk, chunk, chunk,
+						      &barrier, GPU_BUDDY_RANGE_ALLOCATION),
+			       "alloc [1M, 2M) failed\n");
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 2 * chunk, 3 * chunk, chunk, chunk,
+						      &high_a, GPU_BUDDY_RANGE_ALLOCATION),
+			       "alloc [2M, 3M) failed\n");
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 3 * chunk, 4 * chunk, chunk, chunk,
+						      &high_b, GPU_BUDDY_RANGE_ALLOCATION),
+			       "alloc [3M, 4M) failed\n");
+
+	/* [2M, 4M) coalesces into one aligned clear extent; [0, 1M) stays dirty. */
+	gpu_buddy_free_list(&mm, &low_dirty, 0);
+	gpu_buddy_free_list(&mm, &high_a, GPU_BUDDY_CLEARED);
+	gpu_buddy_free_list(&mm, &high_b, GPU_BUDDY_CLEARED);
+
+	/* Dirty 1 MiB range alloc: must land at [0, 1M), not cut the clear extent. */
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 0, mm_size, chunk, chunk,
+						      &dirty_res, GPU_BUDDY_RANGE_ALLOCATION),
+			       "dirty range alloc failed\n");
+	block = list_first_entry(&dirty_res, struct gpu_buddy_block, link);
+	KUNIT_EXPECT_FALSE_MSG(test, gpu_buddy_block_is_clear(block),
+			       "dirty range alloc cut the clear extent (offset=%llx)\n",
+			       gpu_buddy_block_offset(block));
+	KUNIT_EXPECT_EQ(test, gpu_buddy_block_offset(block), 0ULL);
+
+	/*
+	 * The 2 MiB clear extent must still be intact: a clear order-1 range
+	 * allocation has to succeed. Without the guard the extent was cut
+	 * above and this returns -ENOSPC.
+	 */
+	KUNIT_EXPECT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 0, mm_size, 2 * chunk, 2 * chunk,
+						      &clear_res,
+						      GPU_BUDDY_RANGE_ALLOCATION |
+						      GPU_BUDDY_CLEAR_ALLOCATION),
+			       "clear 2M range alloc failed: clear extent was fragmented (-ENOSPC)\n");
+	if (!list_empty(&clear_res)) {
+		block = list_first_entry(&clear_res, struct gpu_buddy_block, link);
+		KUNIT_EXPECT_TRUE(test, gpu_buddy_block_is_clear(block));
+		KUNIT_EXPECT_EQ(test, gpu_buddy_block_offset(block), (u64)(2 * chunk));
+	}
+
+	gpu_buddy_free_list(&mm, &clear_res, GPU_BUDDY_CLEARED);
+	gpu_buddy_free_list(&mm, &dirty_res, 0);
+	gpu_buddy_free_list(&mm, &barrier, 0);
+	gpu_buddy_fini(&mm);
+}
+
 static struct kunit_case gpu_buddy_tests[] = {
 	KUNIT_CASE(gpu_test_buddy_alloc_limit),
 	KUNIT_CASE(gpu_test_buddy_alloc_optimistic),
@@ -1615,6 +1698,7 @@ static struct kunit_case gpu_buddy_tests[] = {
 	KUNIT_CASE(gpu_test_buddy_alloc_clear),
 	KUNIT_CASE(gpu_test_buddy_alloc_range),
 	KUNIT_CASE(gpu_test_buddy_alloc_range_bias),
+	KUNIT_CASE(gpu_test_buddy_alloc_range_clear_guard),
 	KUNIT_CASE_SLOW(gpu_test_buddy_fragmentation_performance),
 	KUNIT_CASE_SLOW(gpu_test_buddy_dirty_tracker_performance),
 	KUNIT_CASE(gpu_test_buddy_alloc_exceeds_max_order),

base-commit: 6f7098738fff3ec7393f924343188cb8e6ebc5d2
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2026-11-04  1:29 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
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2026-11-03 12:56 [PATCH v3] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation Arunpravin Paneer Selvam
2026-11-03 13:09 ` sashiko-bot
2026-11-03 13:58 ` ✗ CI.checkpatch: warning for " Patchwork
2026-11-03 14:00 ` ✓ CI.KUnit: success " Patchwork
2026-11-03 14:33 ` ✓ i915.CI.BAT: " Patchwork
2026-11-03 14:35 ` ✓ Xe.CI.BAT: " Patchwork
2026-11-03 17:40 ` ✗ i915.CI.Full: failure " Patchwork
2026-11-04  1:29 ` ✓ Xe.CI.FULL: success " Patchwork

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