drm: mm: track free areas implicitly

The idea is to track free holes implicitly by marking the allocation
immediatly preceeding a hole.

To avoid an ugly corner case add a dummy head_node to struct drm_mm
to track the hole that spans to complete allocation area when the
memory manager is empty.

To guarantee that there's always a preceeding/following node (that might
be marked as hole_follows == 1), move the mm->node_list list_head to the
head_node.

The main allocator and fair-lru scan code actually becomes simpler.
Only the debug code slightly suffers because free areas are no longer
explicit.

Also add drm_mm_for_each_node (which will be much more useful when
struct drm_mm_node is embeddable).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_mm.c

@@ -64,8 +64,8 @@ static struct drm_mm_node *drm_mm_kmalloc(struct drm_mm *mm, int atomic)
 		else {
 			child =
 			    list_entry(mm->unused_nodes.next,
-				       struct drm_mm_node, free_stack);
-			list_del(&child->free_stack);
+				       struct drm_mm_node, node_list);
+			list_del(&child->node_list);
 			--mm->num_unused;
 		}
 		spin_unlock(&mm->unused_lock);
@@ -94,126 +94,123 @@ int drm_mm_pre_get(struct drm_mm *mm)
 			return ret;
 		}
 		++mm->num_unused;
-		list_add_tail(&node->free_stack, &mm->unused_nodes);
+		list_add_tail(&node->node_list, &mm->unused_nodes);
 	}
 	spin_unlock(&mm->unused_lock);
 	return 0;
 }
 EXPORT_SYMBOL(drm_mm_pre_get);
 
-static int drm_mm_create_tail_node(struct drm_mm *mm,
-				   unsigned long start,
-				   unsigned long size, int atomic)
+static inline unsigned long drm_mm_hole_node_start(struct drm_mm_node *hole_node)
 {
-	struct drm_mm_node *child;
-
-	child = drm_mm_kmalloc(mm, atomic);
-	if (unlikely(child == NULL))
-		return -ENOMEM;
-
-	child->free = 1;
-	child->size = size;
-	child->start = start;
-	child->mm = mm;
-
-	list_add_tail(&child->node_list, &mm->node_list);
-	list_add_tail(&child->free_stack, &mm->free_stack);
-
-	return 0;
+	return hole_node->start + hole_node->size;
 }
 
-static struct drm_mm_node *drm_mm_split_at_start(struct drm_mm_node *parent,
-						 unsigned long size,
-						 int atomic)
+static inline unsigned long drm_mm_hole_node_end(struct drm_mm_node *hole_node)
 {
-	struct drm_mm_node *child;
-
-	child = drm_mm_kmalloc(parent->mm, atomic);
-	if (unlikely(child == NULL))
-		return NULL;
-
-	INIT_LIST_HEAD(&child->free_stack);
+	struct drm_mm_node *next_node =
+		list_entry(hole_node->node_list.next, struct drm_mm_node,
+			   node_list);
 
-	child->size = size;
-	child->start = parent->start;
-	child->mm = parent->mm;
-
-	list_add_tail(&child->node_list, &parent->node_list);
-	INIT_LIST_HEAD(&child->free_stack);
-
-	parent->size -= size;
-	parent->start += size;
-	return child;
+	return next_node->start;
 }
 
-
-struct drm_mm_node *drm_mm_get_block_generic(struct drm_mm_node *node,
+struct drm_mm_node *drm_mm_get_block_generic(struct drm_mm_node *hole_node,
 					     unsigned long size,
 					     unsigned alignment,
 					     int atomic)
 {
 
-	struct drm_mm_node *align_splitoff = NULL;
-	unsigned tmp = 0;
+	struct drm_mm_node *node;
+	struct drm_mm *mm = hole_node->mm;
+	unsigned long tmp = 0, wasted = 0;
+	unsigned long hole_start = drm_mm_hole_node_start(hole_node);
+	unsigned long hole_end = drm_mm_hole_node_end(hole_node);
+
+	BUG_ON(!hole_node->hole_follows);
+
+	node = drm_mm_kmalloc(mm, atomic);
+	if (unlikely(node == NULL))
+		return NULL;
 
 	if (alignment)
-		tmp = node->start % alignment;
+		tmp = hole_start % alignment;
 
-	if (tmp) {
-		align_splitoff =
-		    drm_mm_split_at_start(node, alignment - tmp, atomic);
-		if (unlikely(align_splitoff == NULL))
-			return NULL;
-	}
+	if (!tmp) {
+		hole_node->hole_follows = 0;
+		list_del_init(&hole_node->hole_stack);
+	} else
+		wasted = alignment - tmp;
+
+	node->start = hole_start + wasted;
+	node->size = size;
+	node->mm = mm;
 
-	if (node->size == size) {
-		list_del_init(&node->free_stack);
-		node->free = 0;
+	INIT_LIST_HEAD(&node->hole_stack);
+	list_add(&node->node_list, &hole_node->node_list);
+
+	BUG_ON(node->start + node->size > hole_end);
+
+	if (node->start + node->size < hole_end) {
+		list_add(&node->hole_stack, &mm->hole_stack);
+		node->hole_follows = 1;
 	} else {
-		node = drm_mm_split_at_start(node, size, atomic);
+		node->hole_follows = 0;
 	}
 
-	if (align_splitoff)
-		drm_mm_put_block(align_splitoff);
-
 	return node;
 }
 EXPORT_SYMBOL(drm_mm_get_block_generic);
 
-struct drm_mm_node *drm_mm_get_block_range_generic(struct drm_mm_node *node,
+struct drm_mm_node *drm_mm_get_block_range_generic(struct drm_mm_node *hole_node,
 						unsigned long size,
 						unsigned alignment,
 						unsigned long start,
 						unsigned long end,
 						int atomic)
 {
-	struct drm_mm_node *align_splitoff = NULL;
-	unsigned tmp = 0;
-	unsigned wasted = 0;
+	struct drm_mm_node *node;
+	struct drm_mm *mm = hole_node->mm;
+	unsigned long tmp = 0, wasted = 0;
+	unsigned long hole_start = drm_mm_hole_node_start(hole_node);
+	unsigned long hole_end = drm_mm_hole_node_end(hole_node);
 
-	if (node->start < start)
-		wasted += start - node->start;
+	BUG_ON(!hole_node->hole_follows);
+
+	node = drm_mm_kmalloc(mm, atomic);
+	if (unlikely(node == NULL))
+		return NULL;
+
+	if (hole_start < start)
+		wasted += start - hole_start;
 	if (alignment)
-		tmp = ((node->start + wasted) % alignment);
+		tmp = (hole_start + wasted) % alignment;
 
 	if (tmp)
 		wasted += alignment - tmp;
-	if (wasted) {
-		align_splitoff = drm_mm_split_at_start(node, wasted, atomic);
-		if (unlikely(align_splitoff == NULL))
-			return NULL;
+
+	if (!wasted) {
+		hole_node->hole_follows = 0;
+		list_del_init(&hole_node->hole_stack);
 	}
 
-	if (node->size == size) {
-		list_del_init(&node->free_stack);
-		node->free = 0;
+	node->start = hole_start + wasted;
+	node->size = size;
+	node->mm = mm;
+
+	INIT_LIST_HEAD(&node->hole_stack);
+	list_add(&node->node_list, &hole_node->node_list);
+
+	BUG_ON(node->start + node->size > hole_end);
+	BUG_ON(node->start + node->size > end);
+
+	if (node->start + node->size < hole_end) {
+		list_add(&node->hole_stack, &mm->hole_stack);
+		node->hole_follows = 1;
 	} else {
-		node = drm_mm_split_at_start(node, size, atomic);
+		node->hole_follows = 0;
 	}
 
-	if (align_splitoff)
-		drm_mm_put_block(align_splitoff);
-
 	return node;
 }
 EXPORT_SYMBOL(drm_mm_get_block_range_generic);
@@ -223,66 +220,41 @@ EXPORT_SYMBOL(drm_mm_get_block_range_generic);
  * Otherwise add to the free stack.
  */
 
-void drm_mm_put_block(struct drm_mm_node *cur)
+void drm_mm_put_block(struct drm_mm_node *node)
 {
 
-	struct drm_mm *mm = cur->mm;
-	struct list_head *cur_head = &cur->node_list;
-	struct list_head *root_head = &mm->node_list;
-	struct drm_mm_node *prev_node = NULL;
-	struct drm_mm_node *next_node;
+	struct drm_mm *mm = node->mm;
+	struct drm_mm_node *prev_node;
 
-	int merged = 0;
+	BUG_ON(node->scanned_block || node->scanned_prev_free
+				   || node->scanned_next_free);
 
-	BUG_ON(cur->scanned_block || cur->scanned_prev_free
-				  || cur->scanned_next_free);
+	prev_node =
+	    list_entry(node->node_list.prev, struct drm_mm_node, node_list);
 
-	if (cur_head->prev != root_head) {
-		prev_node =
-		    list_entry(cur_head->prev, struct drm_mm_node, node_list);
-		if (prev_node->free) {
-			prev_node->size += cur->size;
-			merged = 1;
-		}
-	}
-	if (cur_head->next != root_head) {
-		next_node =
-		    list_entry(cur_head->next, struct drm_mm_node, node_list);
-		if (next_node->free) {
-			if (merged) {
-				prev_node->size += next_node->size;
-				list_del(&next_node->node_list);
-				list_del(&next_node->free_stack);
-				spin_lock(&mm->unused_lock);
-				if (mm->num_unused < MM_UNUSED_TARGET) {
-					list_add(&next_node->free_stack,
-						 &mm->unused_nodes);
-					++mm->num_unused;
-				} else
-					kfree(next_node);
-				spin_unlock(&mm->unused_lock);
-			} else {
-				next_node->size += cur->size;
-				next_node->start = cur->start;
-				merged = 1;
-			}
-		}
-	}
-	if (!merged) {
-		cur->free = 1;
-		list_add(&cur->free_stack, &mm->free_stack);
-	} else {
-		list_del(&cur->node_list);
-		spin_lock(&mm->unused_lock);
-		if (mm->num_unused < MM_UNUSED_TARGET) {
-			list_add(&cur->free_stack, &mm->unused_nodes);
-			++mm->num_unused;
-		} else
-			kfree(cur);
-		spin_unlock(&mm->unused_lock);
-	}
-}
+	if (node->hole_follows) {
+		BUG_ON(drm_mm_hole_node_start(node)
+				== drm_mm_hole_node_end(node));
+		list_del(&node->hole_stack);
+	} else
+		BUG_ON(drm_mm_hole_node_start(node)
+				!= drm_mm_hole_node_end(node));
 
+	if (!prev_node->hole_follows) {
+		prev_node->hole_follows = 1;
+		list_add(&prev_node->hole_stack, &mm->hole_stack);
+	} else
+		list_move(&prev_node->hole_stack, &mm->hole_stack);
+
+	list_del(&node->node_list);
+	spin_lock(&mm->unused_lock);
+	if (mm->num_unused < MM_UNUSED_TARGET) {
+		list_add(&node->node_list, &mm->unused_nodes);
+		++mm->num_unused;
+	} else
+		kfree(node);
+	spin_unlock(&mm->unused_lock);
+}
 EXPORT_SYMBOL(drm_mm_put_block);
 
 static int check_free_hole(unsigned long start, unsigned long end,
@@ -319,8 +291,10 @@ struct drm_mm_node *drm_mm_search_free(const struct drm_mm *mm,
 	best = NULL;
 	best_size = ~0UL;
 
-	list_for_each_entry(entry, &mm->free_stack, free_stack) {
-		if (!check_free_hole(entry->start, entry->start + entry->size,
+	list_for_each_entry(entry, &mm->hole_stack, hole_stack) {
+		BUG_ON(!entry->hole_follows);
+		if (!check_free_hole(drm_mm_hole_node_start(entry),
+				     drm_mm_hole_node_end(entry),
 				     size, alignment))
 			continue;
 
@@ -353,12 +327,13 @@ struct drm_mm_node *drm_mm_search_free_in_range(const struct drm_mm *mm,
 	best = NULL;
 	best_size = ~0UL;
 
-	list_for_each_entry(entry, &mm->free_stack, free_stack) {
-		unsigned long adj_start = entry->start < start ?
-			start : entry->start;
-		unsigned long adj_end = entry->start + entry->size > end ?
-			end : entry->start + entry->size;
+	list_for_each_entry(entry, &mm->hole_stack, hole_stack) {
+		unsigned long adj_start = drm_mm_hole_node_start(entry) < start ?
+			start : drm_mm_hole_node_start(entry);
+		unsigned long adj_end = drm_mm_hole_node_end(entry) > end ?
+			end : drm_mm_hole_node_end(entry);
 
+		BUG_ON(!entry->hole_follows);
 		if (!check_free_hole(adj_start, adj_end, size, alignment))
 			continue;
 
@@ -430,70 +405,40 @@ EXPORT_SYMBOL(drm_mm_init_scan_with_range);
 int drm_mm_scan_add_block(struct drm_mm_node *node)
 {
 	struct drm_mm *mm = node->mm;
-	struct list_head *prev_free, *next_free;
-	struct drm_mm_node *prev_node, *next_node;
+	struct drm_mm_node *prev_node;
+	unsigned long hole_start, hole_end;
 	unsigned long adj_start;
 	unsigned long adj_end;
 
 	mm->scanned_blocks++;
 
-	prev_free = next_free = NULL;
-
-	BUG_ON(node->free);
+	BUG_ON(node->scanned_block);
 	node->scanned_block = 1;
-	node->free = 1;
-
-	if (node->node_list.prev != &mm->node_list) {
-		prev_node = list_entry(node->node_list.prev, struct drm_mm_node,
-				       node_list);
-
-		if (prev_node->free) {
-			list_del(&prev_node->node_list);
-
-			node->start = prev_node->start;
-			node->size += prev_node->size;
-
-			prev_node->scanned_prev_free = 1;
-
-			prev_free = &prev_node->free_stack;
-		}
-	}
-
-	if (node->node_list.next != &mm->node_list) {
-		next_node = list_entry(node->node_list.next, struct drm_mm_node,
-				       node_list);
-
-		if (next_node->free) {
-			list_del(&next_node->node_list);
-
-			node->size += next_node->size;
-
-			next_node->scanned_next_free = 1;
 
-			next_free = &next_node->free_stack;
-		}
-	}
+	prev_node = list_entry(node->node_list.prev, struct drm_mm_node,
+			       node_list);
 
-	/* The free_stack list is not used for allocated objects, so these two
-	 * pointers can be abused (as long as no allocations in this memory
-	 * manager happens). */
-	node->free_stack.prev = prev_free;
-	node->free_stack.next = next_free;
+	node->scanned_preceeds_hole = prev_node->hole_follows;
+	prev_node->hole_follows = 1;
+	list_del(&node->node_list);
+	node->node_list.prev = &prev_node->node_list;
 
+	hole_start = drm_mm_hole_node_start(prev_node);
+	hole_end = drm_mm_hole_node_end(prev_node);
 	if (mm->scan_check_range) {
-		adj_start = node->start < mm->scan_start ?
-			mm->scan_start : node->start;
-		adj_end = node->start + node->size > mm->scan_end ?
-			mm->scan_end : node->start + node->size;
+		adj_start = hole_start < mm->scan_start ?
+			mm->scan_start : hole_start;
+		adj_end = hole_end > mm->scan_end ?
+			mm->scan_end : hole_end;
 	} else {
-		adj_start = node->start;
-		adj_end = node->start + node->size;
+		adj_start = hole_start;
+		adj_end = hole_end;
 	}
 
 	if (check_free_hole(adj_start , adj_end,
 			    mm->scan_size, mm->scan_alignment)) {
-		mm->scan_hit_start = node->start;
-		mm->scan_hit_size = node->size;
+		mm->scan_hit_start = hole_start;
+		mm->scan_hit_size = hole_end;
 
 		return 1;
 	}
@@ -519,39 +464,19 @@ EXPORT_SYMBOL(drm_mm_scan_add_block);
 int drm_mm_scan_remove_block(struct drm_mm_node *node)
 {
 	struct drm_mm *mm = node->mm;
-	struct drm_mm_node *prev_node, *next_node;
+	struct drm_mm_node *prev_node;
 
 	mm->scanned_blocks--;
 
 	BUG_ON(!node->scanned_block);
 	node->scanned_block = 0;
-	node->free = 0;
-
-	prev_node = list_entry(node->free_stack.prev, struct drm_mm_node,
-			       free_stack);
-	next_node = list_entry(node->free_stack.next, struct drm_mm_node,
-			       free_stack);
-
-	if (prev_node) {
-		BUG_ON(!prev_node->scanned_prev_free);
-		prev_node->scanned_prev_free = 0;
-
-		list_add_tail(&prev_node->node_list, &node->node_list);
 
-		node->start = prev_node->start + prev_node->size;
-		node->size -= prev_node->size;
-	}
-
-	if (next_node) {
-		BUG_ON(!next_node->scanned_next_free);
-		next_node->scanned_next_free = 0;
-
-		list_add(&next_node->node_list, &node->node_list);
-
-		node->size -= next_node->size;
-	}
+	prev_node = list_entry(node->node_list.prev, struct drm_mm_node,
+			       node_list);
 
-	INIT_LIST_HEAD(&node->free_stack);
+	prev_node->hole_follows = node->scanned_preceeds_hole;
+	INIT_LIST_HEAD(&node->node_list);
+	list_add(&node->node_list, &prev_node->node_list);
 
 	/* Only need to check for containement because start&size for the
 	 * complete resulting free block (not just the desired part) is
@@ -568,7 +493,7 @@ EXPORT_SYMBOL(drm_mm_scan_remove_block);
 
 int drm_mm_clean(struct drm_mm * mm)
 {
-	struct list_head *head = &mm->node_list;
+	struct list_head *head = &mm->head_node.node_list;
 
 	return (head->next->next == head);
 }
@@ -576,38 +501,40 @@ EXPORT_SYMBOL(drm_mm_clean);
 
 int drm_mm_init(struct drm_mm * mm, unsigned long start, unsigned long size)
 {
-	INIT_LIST_HEAD(&mm->node_list);
-	INIT_LIST_HEAD(&mm->free_stack);
+	INIT_LIST_HEAD(&mm->hole_stack);
 	INIT_LIST_HEAD(&mm->unused_nodes);
 	mm->num_unused = 0;
 	mm->scanned_blocks = 0;
 	spin_lock_init(&mm->unused_lock);
 
-	return drm_mm_create_tail_node(mm, start, size, 0);
+	/* Clever trick to avoid a special case in the free hole tracking. */
+	INIT_LIST_HEAD(&mm->head_node.node_list);
+	INIT_LIST_HEAD(&mm->head_node.hole_stack);
+	mm->head_node.hole_follows = 1;
+	mm->head_node.scanned_block = 0;
+	mm->head_node.scanned_prev_free = 0;
+	mm->head_node.scanned_next_free = 0;
+	mm->head_node.mm = mm;
+	mm->head_node.start = start + size;
+	mm->head_node.size = start - mm->head_node.start;
+	list_add_tail(&mm->head_node.hole_stack, &mm->hole_stack);
+
+	return 0;
 }
 EXPORT_SYMBOL(drm_mm_init);
 
 void drm_mm_takedown(struct drm_mm * mm)
 {
-	struct list_head *bnode = mm->free_stack.next;
-	struct drm_mm_node *entry;
-	struct drm_mm_node *next;
+	struct drm_mm_node *entry, *next;
 
-	entry = list_entry(bnode, struct drm_mm_node, free_stack);
-
-	if (entry->node_list.next != &mm->node_list ||
-	    entry->free_stack.next != &mm->free_stack) {
+	if (!list_empty(&mm->head_node.node_list)) {
 		DRM_ERROR("Memory manager not clean. Delaying takedown\n");
 		return;
 	}
 
-	list_del(&entry->free_stack);
-	list_del(&entry->node_list);
-	kfree(entry);
-
 	spin_lock(&mm->unused_lock);
-	list_for_each_entry_safe(entry, next, &mm->unused_nodes, free_stack) {
-		list_del(&entry->free_stack);
+	list_for_each_entry_safe(entry, next, &mm->unused_nodes, node_list) {
+		list_del(&entry->node_list);
 		kfree(entry);
 		--mm->num_unused;
 	}
@@ -620,19 +547,37 @@ EXPORT_SYMBOL(drm_mm_takedown);
 void drm_mm_debug_table(struct drm_mm *mm, const char *prefix)
 {
 	struct drm_mm_node *entry;
-	int total_used = 0, total_free = 0, total = 0;
-
-	list_for_each_entry(entry, &mm->node_list, node_list) {
-		printk(KERN_DEBUG "%s 0x%08lx-0x%08lx: %8ld: %s\n",
+	unsigned long total_used = 0, total_free = 0, total = 0;
+	unsigned long hole_start, hole_end, hole_size;
+
+	hole_start = drm_mm_hole_node_start(&mm->head_node);
+	hole_end = drm_mm_hole_node_end(&mm->head_node);
+	hole_size = hole_end - hole_start;
+	if (hole_size)
+		printk(KERN_DEBUG "%s 0x%08lx-0x%08lx: %8lu: free\n",
+			prefix, hole_start, hole_end,
+			hole_size);
+	total_free += hole_size;
+
+	drm_mm_for_each_node(entry, mm) {
+		printk(KERN_DEBUG "%s 0x%08lx-0x%08lx: %8lu: used\n",
 			prefix, entry->start, entry->start + entry->size,
-			entry->size, entry->free ? "free" : "used");
-		total += entry->size;
-		if (entry->free)
-			total_free += entry->size;
-		else
-			total_used += entry->size;
+			entry->size);
+		total_used += entry->size;
+
+		if (entry->hole_follows) {
+			hole_start = drm_mm_hole_node_start(entry);
+			hole_end = drm_mm_hole_node_end(entry);
+			hole_size = hole_end - hole_start;
+			printk(KERN_DEBUG "%s 0x%08lx-0x%08lx: %8lu: free\n",
+				prefix, hole_start, hole_end,
+				hole_size);
+			total_free += hole_size;
+		}
 	}
-	printk(KERN_DEBUG "%s total: %d, used %d free %d\n", prefix, total,
+	total = total_free + total_used;
+
+	printk(KERN_DEBUG "%s total: %lu, used %lu free %lu\n", prefix, total,
 		total_used, total_free);
 }
 EXPORT_SYMBOL(drm_mm_debug_table);
@@ -641,17 +586,34 @@ EXPORT_SYMBOL(drm_mm_debug_table);
 int drm_mm_dump_table(struct seq_file *m, struct drm_mm *mm)
 {
 	struct drm_mm_node *entry;
-	int total_used = 0, total_free = 0, total = 0;
-
-	list_for_each_entry(entry, &mm->node_list, node_list) {
-		seq_printf(m, "0x%08lx-0x%08lx: 0x%08lx: %s\n", entry->start, entry->start + entry->size, entry->size, entry->free ? "free" : "used");
-		total += entry->size;
-		if (entry->free)
-			total_free += entry->size;
-		else
-			total_used += entry->size;
+	unsigned long total_used = 0, total_free = 0, total = 0;
+	unsigned long hole_start, hole_end, hole_size;
+
+	hole_start = drm_mm_hole_node_start(&mm->head_node);
+	hole_end = drm_mm_hole_node_end(&mm->head_node);
+	hole_size = hole_end - hole_start;
+	if (hole_size)
+		seq_printf(m, "0x%08lx-0x%08lx: 0x%08lx: free\n",
+				hole_start, hole_end, hole_size);
+	total_free += hole_size;
+
+	drm_mm_for_each_node(entry, mm) {
+		seq_printf(m, "0x%08lx-0x%08lx: 0x%08lx: used\n",
+				entry->start, entry->start + entry->size,
+				entry->size);
+		total_used += entry->size;
+		if (entry->hole_follows) {
+			hole_start = drm_mm_hole_node_start(&mm->head_node);
+			hole_end = drm_mm_hole_node_end(&mm->head_node);
+			hole_size = hole_end - hole_start;
+			seq_printf(m, "0x%08lx-0x%08lx: 0x%08lx: free\n",
+					hole_start, hole_end, hole_size);
+			total_free += hole_size;
+		}
 	}
-	seq_printf(m, "total: %d, used %d free %d\n", total, total_used, total_free);
+	total = total_free + total_used;
+
+	seq_printf(m, "total: %lu, used %lu free %lu\n", total, total_used, total_free);
 	return 0;
 }
 EXPORT_SYMBOL(drm_mm_dump_table);

include/drm/drm_mm.h

@@ -42,23 +42,24 @@
 #endif
 
 struct drm_mm_node {
-	struct list_head free_stack;
 	struct list_head node_list;
-	unsigned free : 1;
+	struct list_head hole_stack;
+	unsigned hole_follows : 1;
 	unsigned scanned_block : 1;
 	unsigned scanned_prev_free : 1;
 	unsigned scanned_next_free : 1;
+	unsigned scanned_preceeds_hole : 1;
 	unsigned long start;
 	unsigned long size;
 	struct drm_mm *mm;
 };
 
 struct drm_mm {
-	/* List of free memory blocks, most recently freed ordered. */
-	struct list_head free_stack;
-	/* List of all memory nodes, ordered according to the (increasing) start
-	 * address of the memory node. */
-	struct list_head node_list;
+	/* List of all memory nodes that immediatly preceed a free hole. */
+	struct list_head hole_stack;
+	/* head_node.node_list is the list of all memory nodes, ordered
+	 * according to the (increasing) start address of the memory node. */
+	struct drm_mm_node head_node;
 	struct list_head unused_nodes;
 	int num_unused;
 	spinlock_t unused_lock;
@@ -74,9 +75,11 @@ struct drm_mm {
 
 static inline bool drm_mm_initialized(struct drm_mm *mm)
 {
-	return mm->free_stack.next;
+	return mm->hole_stack.next;
 }
-
+#define drm_mm_for_each_node(entry, mm) list_for_each_entry(entry, \
+						&(mm)->head_node.node_list, \
+						node_list);
 /*
  * Basic range manager support (drm_mm.c)
  */