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* [PATCH v4 1/3] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation
@ 2026-10-09 10:05 Arunpravin Paneer Selvam
  2026-10-09 10:05 ` [PATCH v4 2/3] gpu/buddy: add range-restricted contiguous allocation fallback Arunpravin Paneer Selvam
                   ` (5 more replies)
  0 siblings, 6 replies; 9+ messages in thread
From: Arunpravin Paneer Selvam @ 2026-10-09 10:05 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.

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                | 71 ++++++++++++++----------------
 drivers/gpu/tests/gpu_buddy_test.c | 65 +++++++++++++++++++++++++++
 2 files changed, 99 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
index 2f2aaadafe35..6566bad4fef1 100644
--- a/drivers/gpu/buddy.c
+++ b/drivers/gpu/buddy.c
@@ -1240,11 +1240,19 @@ 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;
+
+	return needs_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 +1266,7 @@ __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 +1304,9 @@ __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 +1324,8 @@ __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 +1340,24 @@ __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 +1921,7 @@ __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 b75d32ca6ca0..3eaa261571bf 100644
--- a/drivers/gpu/tests/gpu_buddy_test.c
+++ b/drivers/gpu/tests/gpu_buddy_test.c
@@ -1597,6 +1597,70 @@ 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(high_clear_a);
+	LIST_HEAD(high_clear_b);
+	LIST_HEAD(low_dirty);
+	struct gpu_buddy mm;
+	LIST_HEAD(barrier);
+	LIST_HEAD(result);
+
+	KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_init(&mm, mm_size, chunk),
+			       "buddy_init failed\n");
+
+	/*
+	 * Lay out a 4 MiB aperture as three regions:
+	 *
+	 *   [0,  1M)   dirty free
+	 *   [1M, 2M)   allocated  (barrier, keeps the two halves un-mergeable)
+	 *   [2M, 4M)   clear free (one naturally aligned 2 MiB extent)
+	 *
+	 * A dirty (non-clear) range allocation must take the low dirty block
+	 * and leave the large clear extent intact. Without the guard the
+	 * top-down search cuts the higher clear extent instead and returns a
+	 * clear block -- the interleaving that fragments the aperture and
+	 * ultimately fails a large same-class scanout allocation.
+	 */
+	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_clear_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_clear_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_clear_a, GPU_BUDDY_CLEARED);
+	gpu_buddy_free_list(&mm, &high_clear_b, GPU_BUDDY_CLEARED);
+
+	KUNIT_ASSERT_FALSE_MSG(test,
+			       gpu_buddy_alloc_blocks(&mm, 0, mm_size, chunk, chunk,
+						      &result, GPU_BUDDY_RANGE_ALLOCATION),
+			       "dirty range alloc failed\n");
+
+	block = list_first_entry(&result, 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));
+
+	gpu_buddy_free_list(&mm, &result, 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),
@@ -1606,6 +1670,7 @@ 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: f146c6086b792cb2c6b3ce5106f0cce62e408df8
-- 
2.43.0


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Thread overview: 9+ messages (download: mbox.gz follow: Atom feed
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2026-10-09 10:05 [PATCH v4 1/3] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation Arunpravin Paneer Selvam
2026-10-09 10:05 ` [PATCH v4 2/3] gpu/buddy: add range-restricted contiguous allocation fallback Arunpravin Paneer Selvam
2026-10-09 10:23   ` sashiko-bot
2026-10-09 10:05 ` [PATCH v4 3/3] gpu/buddy: search lower orders in contiguous try-harder fallback Arunpravin Paneer Selvam
2026-10-09 10:17 ` [PATCH v4 1/3] gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation sashiko-bot
2026-10-09 12:07 ` ✓ i915.CI.BAT: success for series starting with [v4,1/3] " Patchwork
2026-10-09 14:58 ` ✓ i915.CI.Full: " Patchwork
2026-10-13 14:31 ` [PATCH v4 1/3] " Arunpravin Paneer Selvam
2026-10-13 15:06   ` Matthew Auld

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