[PATCH 1/3] drm: Track drm_mm nodes with an interval tree

[Chris Wilson]

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.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: dri-devel at lists.freedesktop.org
---
 drivers/gpu/drm/Kconfig  |  1 +
 drivers/gpu/drm/drm_mm.c | 71 ++++++++++++++++++++++++++++++++----------------
 include/drm/drm_mm.h     |  5 ++++
 3 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 06ae5008c5ed..e25050a5a843 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -12,6 +12,7 @@ menuconfig DRM
 	select I2C
 	select I2C_ALGOBIT
 	select DMA_SHARED_BUFFER
+	select INTERVAL_TREE
 	help
 	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
 	  introduced in XFree86 4.0. If you say Y here, you need to select
diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 04de6fd88f8c..e3acd860f738 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -153,6 +153,10 @@ 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);
 
+	node->it.start = node->start;
+	node->it.last = node->start + size - 1;
+	interval_tree_insert(&node->it, &mm->interval_tree);
+
 	BUG_ON(node->start + node->size > adj_end);
 
 	node->hole_follows = 0;
@@ -178,39 +182,53 @@ 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)
 {
-	struct drm_mm_node *hole;
 	u64 end = node->start + node->size;
-	u64 hole_start;
-	u64 hole_end;
-
-	BUG_ON(node == NULL);
+	struct interval_tree_node *it;
+	struct drm_mm_node *hole;
+	u64 hole_start, hole_end;
 
 	/* 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;
+	it = interval_tree_iter_first(&mm->interval_tree,
+				      node->start, (u64)-1);
+	if (it == NULL) {
+		hole = list_last_entry(&mm->head_node.node_list,
+				       struct drm_mm_node, node_list);
+	} else {
+		hole = container_of(it, typeof(*hole), it);
+		if (hole->start <= node->start)
+			return -ENOSPC;
+
+		hole = list_last_entry(&hole->node_list,
+				       struct drm_mm_node, node_list);
+	}
 
-		node->mm = mm;
-		node->allocated = 1;
+	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;
 
-		INIT_LIST_HEAD(&node->hole_stack);
-		list_add(&node->node_list, &hole->node_list);
+	node->mm = mm;
+	node->allocated = 1;
 
-		if (node->start == hole_start) {
-			hole->hole_follows = 0;
-			list_del_init(&hole->hole_stack);
-		}
+	INIT_LIST_HEAD(&node->hole_stack);
+	list_add(&node->node_list, &hole->node_list);
 
-		node->hole_follows = 0;
-		if (end != hole_end) {
-			list_add(&node->hole_stack, &mm->hole_stack);
-			node->hole_follows = 1;
-		}
+	node->it.start = node->start;
+	node->it.last = node->start + node->size - 1;
+	interval_tree_insert(&node->it, &mm->interval_tree);
 
-		return 0;
+	if (node->start == hole_start) {
+		hole->hole_follows = 0;
+		list_del_init(&hole->hole_stack);
 	}
 
-	return -ENOSPC;
+	node->hole_follows = 0;
+	if (end != hole_end) {
+		list_add(&node->hole_stack, &mm->hole_stack);
+		node->hole_follows = 1;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL(drm_mm_reserve_node);
 
@@ -300,6 +318,10 @@ 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);
 
+	node->it.start = node->start;
+	node->it.last = node->start + node->size - 1;
+	interval_tree_insert(&node->it, &mm->interval_tree);
+
 	BUG_ON(node->start < start);
 	BUG_ON(node->start < adj_start);
 	BUG_ON(node->start + node->size > adj_end);
@@ -388,6 +410,7 @@ void drm_mm_remove_node(struct drm_mm_node *node)
 	} else
 		list_move(&prev_node->hole_stack, &mm->hole_stack);
 
+	interval_tree_remove(&node->it, &mm->interval_tree);
 	list_del(&node->node_list);
 	node->allocated = 0;
 }
@@ -756,6 +779,8 @@ 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);
diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h
index 0de6290df4da..6d531fe529bf 100644
--- a/include/drm/drm_mm.h
+++ b/include/drm/drm_mm.h
@@ -37,6 +37,7 @@
  * Generic range manager structs
  */
 #include <linux/bug.h>
+#include <linux/interval_tree.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 interval_tree_node it;
 	unsigned hole_follows : 1;
 	unsigned scanned_block : 1;
 	unsigned scanned_prev_free : 1;
@@ -79,6 +81,9 @@ 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;
-- 
2.6.0