drm: Track drm_mm nodes with an interval tree

In addition to the last-in/first-out stack for accessing drm_mm nodes,
we occasionally and in the future often want to find a drm_mm_node by an
address. To do so efficiently we need to track the nodes in an interval
tree - lookups for a particular address will then be O(lg(N)), where N
is the number of nodes in the range manager as opposed to O(N).
Insertion however gains an extra O(lg(N)) step for all nodes
irrespective of whether the interval tree is in use. For future i915
patches, eliminating the linear walk is a significant improvement.

v2: Use generic interval-tree template for u64 and faster insertion.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470236651-678-1-git-send-email-chris@chris-wilson.co.uk

Author: ickle

drivers/gpu/drm/drm_mm.c

@@ -46,6 +46,7 @@
 #include <linux/slab.h>
 #include <linux/seq_file.h>
 #include <linux/export.h>
+#include <linux/interval_tree_generic.h>
 
 /**
  * DOC: Overview
@@ -103,6 +104,72 @@ static struct drm_mm_node *drm_mm_search_free_in_range_generic(const struct drm_
 						u64 end,
 						enum drm_mm_search_flags flags);
 
+#define START(node) ((node)->start)
+#define LAST(node)  ((node)->start + (node)->size - 1)
+
+INTERVAL_TREE_DEFINE(struct drm_mm_node, rb,
+		     u64, __subtree_last,
+		     START, LAST, static inline, drm_mm_interval_tree)
+
+struct drm_mm_node *
+drm_mm_interval_first(struct drm_mm *mm, u64 start, u64 last)
+{
+	return drm_mm_interval_tree_iter_first(&mm->interval_tree,
+					       start, last);
+}
+EXPORT_SYMBOL(drm_mm_interval_first);
+
+struct drm_mm_node *
+drm_mm_interval_next(struct drm_mm_node *node, u64 start, u64 last)
+{
+	return drm_mm_interval_tree_iter_next(node, start, last);
+}
+EXPORT_SYMBOL(drm_mm_interval_next);
+
+static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
+					  struct drm_mm_node *node)
+{
+	struct drm_mm *mm = hole_node->mm;
+	struct rb_node **link, *rb;
+	struct drm_mm_node *parent;
+
+	node->__subtree_last = LAST(node);
+
+	if (hole_node->allocated) {
+		rb = &hole_node->rb;
+		while (rb) {
+			parent = rb_entry(rb, struct drm_mm_node, rb);
+			if (parent->__subtree_last >= node->__subtree_last)
+				break;
+
+			parent->__subtree_last = node->__subtree_last;
+			rb = rb_parent(rb);
+		}
+
+		rb = &hole_node->rb;
+		link = &hole_node->rb.rb_right;
+	} else {
+		rb = NULL;
+		link = &mm->interval_tree.rb_node;
+	}
+
+	while (*link) {
+		rb = *link;
+		parent = rb_entry(rb, struct drm_mm_node, rb);
+		if (parent->__subtree_last < node->__subtree_last)
+			parent->__subtree_last = node->__subtree_last;
+		if (node->start < parent->start)
+			link = &parent->rb.rb_left;
+		else
+			link = &parent->rb.rb_right;
+	}
+
+	rb_link_node(&node->rb, rb, link);
+	rb_insert_augmented(&node->rb,
+			    &mm->interval_tree,
+			    &drm_mm_interval_tree_augment);
+}
+
 static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
 				 struct drm_mm_node *node,
 				 u64 size, unsigned alignment,
@@ -153,6 +220,8 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
 	INIT_LIST_HEAD(&node->hole_stack);
 	list_add(&node->node_list, &hole_node->node_list);
 
+	drm_mm_interval_tree_add_node(hole_node, node);
+
 	BUG_ON(node->start + node->size > adj_end);
 
 	node->hole_follows = 0;
@@ -178,41 +247,52 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
  */
 int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
 {
+	u64 end = node->start + node->size;
 	struct drm_mm_node *hole;
-	u64 end;
-	u64 hole_start;
-	u64 hole_end;
-
-	BUG_ON(node == NULL);
+	u64 hole_start, hole_end;
 
 	end = node->start + node->size;
 
 	/* Find the relevant hole to add our node to */
-	drm_mm_for_each_hole(hole, mm, hole_start, hole_end) {
-		if (hole_start > node->start || hole_end < end)
-			continue;
+	hole = drm_mm_interval_tree_iter_first(&mm->interval_tree,
+					       node->start, ~(u64)0);
+	if (hole) {
+		if (hole->start < end)
+			return -ENOSPC;
+	} else {
+		hole = list_entry(&mm->head_node.node_list,
+				  typeof(*hole), node_list);
+	}
 
-		node->mm = mm;
-		node->allocated = 1;
+	hole = list_last_entry(&hole->node_list, typeof(*hole), node_list);
+	if (!hole->hole_follows)
+		return -ENOSPC;
 
-		INIT_LIST_HEAD(&node->hole_stack);
-		list_add(&node->node_list, &hole->node_list);
+	hole_start = __drm_mm_hole_node_start(hole);
+	hole_end = __drm_mm_hole_node_end(hole);
+	if (hole_start > node->start || hole_end < end)
+		return -ENOSPC;
 
-		if (node->start == hole_start) {
-			hole->hole_follows = 0;
-			list_del_init(&hole->hole_stack);
-		}
+	node->mm = mm;
+	node->allocated = 1;
 
-		node->hole_follows = 0;
-		if (end != hole_end) {
-			list_add(&node->hole_stack, &mm->hole_stack);
-			node->hole_follows = 1;
-		}
+	INIT_LIST_HEAD(&node->hole_stack);
+	list_add(&node->node_list, &hole->node_list);
 
-		return 0;
+	drm_mm_interval_tree_add_node(hole, node);
+
+	if (node->start == hole_start) {
+		hole->hole_follows = 0;
+		list_del_init(&hole->hole_stack);
+	}
+
+	node->hole_follows = 0;
+	if (end != hole_end) {
+		list_add(&node->hole_stack, &mm->hole_stack);
+		node->hole_follows = 1;
 	}
 
-	return -ENOSPC;
+	return 0;
 }
 EXPORT_SYMBOL(drm_mm_reserve_node);
 
@@ -302,6 +382,8 @@ static void drm_mm_insert_helper_range(struct drm_mm_node *hole_node,
 	INIT_LIST_HEAD(&node->hole_stack);
 	list_add(&node->node_list, &hole_node->node_list);
 
+	drm_mm_interval_tree_add_node(hole_node, node);
+
 	BUG_ON(node->start < start);
 	BUG_ON(node->start < adj_start);
 	BUG_ON(node->start + node->size > adj_end);
@@ -390,6 +472,7 @@ void drm_mm_remove_node(struct drm_mm_node *node)
 	} else
 		list_move(&prev_node->hole_stack, &mm->hole_stack);
 
+	drm_mm_interval_tree_remove(node, &mm->interval_tree);
 	list_del(&node->node_list);
 	node->allocated = 0;
 }
@@ -516,11 +599,13 @@ void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new)
 {
 	list_replace(&old->node_list, &new->node_list);
 	list_replace(&old->hole_stack, &new->hole_stack);
+	rb_replace_node(&old->rb, &new->rb, &old->mm->interval_tree);
 	new->hole_follows = old->hole_follows;
 	new->mm = old->mm;
 	new->start = old->start;
 	new->size = old->size;
 	new->color = old->color;
+	new->__subtree_last = old->__subtree_last;
 
 	old->allocated = 0;
 	new->allocated = 1;
@@ -758,6 +843,8 @@ void drm_mm_init(struct drm_mm * mm, u64 start, u64 size)
 	mm->head_node.size = start - mm->head_node.start;
 	list_add_tail(&mm->head_node.hole_stack, &mm->hole_stack);
 
+	mm->interval_tree = RB_ROOT;
+
 	mm->color_adjust = NULL;
 }
 EXPORT_SYMBOL(drm_mm_init);

include/drm/drm_mm.h

@@ -37,6 +37,7 @@
  * Generic range manager structs
  */
 #include <linux/bug.h>
+#include <linux/rbtree.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
@@ -61,6 +62,7 @@ enum drm_mm_allocator_flags {
 struct drm_mm_node {
 	struct list_head node_list;
 	struct list_head hole_stack;
+	struct rb_node rb;
 	unsigned hole_follows : 1;
 	unsigned scanned_block : 1;
 	unsigned scanned_prev_free : 1;
@@ -70,6 +72,7 @@ struct drm_mm_node {
 	unsigned long color;
 	u64 start;
 	u64 size;
+	u64 __subtree_last;
 	struct drm_mm *mm;
 };
 
@@ -79,6 +82,9 @@ struct drm_mm {
 	/* 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;
+	/* Keep an interval_tree for fast lookup of drm_mm_nodes by address. */
+	struct rb_root interval_tree;
+
 	unsigned int scan_check_range : 1;
 	unsigned scan_alignment;
 	unsigned long scan_color;
@@ -295,6 +301,12 @@ void drm_mm_init(struct drm_mm *mm,
 void drm_mm_takedown(struct drm_mm *mm);
 bool drm_mm_clean(struct drm_mm *mm);
 
+struct drm_mm_node *
+drm_mm_interval_first(struct drm_mm *mm, u64 start, u64 last);
+
+struct drm_mm_node *
+drm_mm_interval_next(struct drm_mm_node *node, u64 start, u64 last);
+
 void drm_mm_init_scan(struct drm_mm *mm,
 		      u64 size,
 		      unsigned alignment,