Date:	Tue, 01 Jun 2010 19:42:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Fabio Checconi <fabio@...dalf.sssup.it>
Subject: Re: [PATCH] rbtree: undo augmented damage -v2

On Tue, 2010-06-01 at 10:34 -0700, Venkatesh Pallipadi wrote:
> 
> Yes. This will cover all the cases on insert. But on erase, there is
> still a case where a rotate of sibling node is done during the
> re-coloration process. There we have a child change on sibling's
> child. I am not able to think of any easy way to handle that case.

Let me go draw some figures with pen and paper to match up the erase
path with the rb_augment_erase_begin() code, because I can't quite spot
the case we're missing.

If you have it handy, ascii art might help..

Below a new patch with the missing bit folded into the generic code.


---
Subject: rbtree: Undo augmented damage 
From: Peter Zijlstra <peterz@...radead.org>
Date: Sat, 29 May 2010 15:31:43 +0200

Reimplement augmented RB-trees without sprinkling extra branches
all over the RB-tree code (which lives in the scheduler hot path).

This approach is 'borrowed' from Fabio's BFQ implementation and
relies on traversing the rebalance path after the RB-tree-op to
correct the heap property for insertion/removal and make up for
the damage done by the tree rotations.

For insertion the rebalance path is trivially that from the new
node upwards to the root, for removal it is that from the deepest
node in the path from the to be removed node that will still
be around after the removal.

Cc: Fabio Checconi <fabio@...dalf.sssup.it>
Cc: suresh.b.siddha@...el.com
Cc: venki@...gle.com
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 arch/x86/mm/pat_rbtree.c |   34 ++-----------
 include/linux/rbtree.h   |   13 +++--
 lib/rbtree.c             |  116 +++++++++++++++++++++++++++++------------------
 3 files changed, 87 insertions(+), 76 deletions(-)

Index: linux-2.6/arch/x86/mm/pat_rbtree.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/pat_rbtree.c
+++ linux-2.6/arch/x86/mm/pat_rbtree.c
@@ -34,8 +34,7 @@
  * memtype_lock protects the rbtree.
  */
 
-static void memtype_rb_augment_cb(struct rb_node *node);
-static struct rb_root memtype_rbroot = RB_AUGMENT_ROOT(&memtype_rb_augment_cb);
+static struct rb_root memtype_rbroot = RB_ROOT;
 
 static int is_node_overlap(struct memtype *node, u64 start, u64 end)
 {
@@ -56,7 +55,7 @@ static u64 get_subtree_max_end(struct rb
 }
 
 /* Update 'subtree_max_end' for a node, based on node and its children */
-static void update_node_max_end(struct rb_node *node)
+static void memtype_rb_augment_cb(struct rb_node *node, void *__unused)
 {
 	struct memtype *data;
 	u64 max_end, child_max_end;
@@ -78,25 +77,6 @@ static void update_node_max_end(struct r
 	data->subtree_max_end = max_end;
 }
 
-/* Update 'subtree_max_end' for a node and all its ancestors */
-static void update_path_max_end(struct rb_node *node)
-{
-	u64 old_max_end, new_max_end;
-
-	while (node) {
-		struct memtype *data = container_of(node, struct memtype, rb);
-
-		old_max_end = data->subtree_max_end;
-		update_node_max_end(node);
-		new_max_end = data->subtree_max_end;
-
-		if (new_max_end == old_max_end)
-			break;
-
-		node = rb_parent(node);
-	}
-}
-
 /* Find the first (lowest start addr) overlapping range from rb tree */
 static struct memtype *memtype_rb_lowest_match(struct rb_root *root,
 				u64 start, u64 end)
@@ -190,12 +170,6 @@ failure:
 	return -EBUSY;
 }
 
-static void memtype_rb_augment_cb(struct rb_node *node)
-{
-	if (node)
-		update_path_max_end(node);
-}
-
 static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
 {
 	struct rb_node **node = &(root->rb_node);
@@ -213,6 +187,7 @@ static void memtype_rb_insert(struct rb_
 
 	rb_link_node(&newdata->rb, parent, node);
 	rb_insert_color(&newdata->rb, root);
+	rb_augment_insert(&newdata->rb, memtype_rb_augment_cb, NULL);
 }
 
 int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
@@ -233,13 +208,16 @@ int rbt_memtype_check_insert(struct memt
 
 struct memtype *rbt_memtype_erase(u64 start, u64 end)
 {
+	struct rb_node *deepest;
 	struct memtype *data;
 
 	data = memtype_rb_exact_match(&memtype_rbroot, start, end);
 	if (!data)
 		goto out;
 
+	deepest = rb_augment_erase_begin(&data->rb);
 	rb_erase(&data->rb, &memtype_rbroot);
+	rb_augment_erase_end(deepest, memtype_rb_augment_cb, NULL);
 out:
 	return data;
 }
Index: linux-2.6/include/linux/rbtree.h
===================================================================
--- linux-2.6.orig/include/linux/rbtree.h
+++ linux-2.6/include/linux/rbtree.h
@@ -110,7 +110,6 @@ struct rb_node
 struct rb_root
 {
 	struct rb_node *rb_node;
-	void (*augment_cb)(struct rb_node *node);
 };
 
 
@@ -130,9 +129,7 @@ static inline void rb_set_color(struct r
 	rb->rb_parent_color = (rb->rb_parent_color & ~1) | color;
 }
 
-#define RB_ROOT	(struct rb_root) { NULL, NULL, }
-#define RB_AUGMENT_ROOT(x)	(struct rb_root) { NULL, x}
-
+#define RB_ROOT	(struct rb_root) { NULL, }
 #define	rb_entry(ptr, type, member) container_of(ptr, type, member)
 
 #define RB_EMPTY_ROOT(root)	((root)->rb_node == NULL)
@@ -142,6 +139,14 @@ static inline void rb_set_color(struct r
 extern void rb_insert_color(struct rb_node *, struct rb_root *);
 extern void rb_erase(struct rb_node *, struct rb_root *);
 
+typedef void (*rb_augment_f)(struct rb_node *node, void *data);
+
+extern void rb_augment_insert(struct rb_node *node,
+			      rb_augment_f func, void *data);
+extern struct rb_node *rb_augment_erase_begin(struct rb_node *node);
+extern void rb_augment_erase_end(struct rb_node *node,
+				 rb_augment_f func, void *data);
+
 /* Find logical next and previous nodes in a tree */
 extern struct rb_node *rb_next(const struct rb_node *);
 extern struct rb_node *rb_prev(const struct rb_node *);
Index: linux-2.6/lib/rbtree.c
===================================================================
--- linux-2.6.orig/lib/rbtree.c
+++ linux-2.6/lib/rbtree.c
@@ -44,11 +44,6 @@ static void __rb_rotate_left(struct rb_n
 	else
 		root->rb_node = right;
 	rb_set_parent(node, right);
-
-	if (root->augment_cb) {
-		root->augment_cb(node);
-		root->augment_cb(right);
-	}
 }
 
 static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
@@ -72,20 +67,12 @@ static void __rb_rotate_right(struct rb_
 	else
 		root->rb_node = left;
 	rb_set_parent(node, left);
-
-	if (root->augment_cb) {
-		root->augment_cb(node);
-		root->augment_cb(left);
-	}
 }
 
 void rb_insert_color(struct rb_node *node, struct rb_root *root)
 {
 	struct rb_node *parent, *gparent;
 
-	if (root->augment_cb)
-		root->augment_cb(node);
-
 	while ((parent = rb_parent(node)) && rb_is_red(parent))
 	{
 		gparent = rb_parent(parent);
@@ -240,15 +227,12 @@ void rb_erase(struct rb_node *node, stru
 	else
 	{
 		struct rb_node *old = node, *left;
-		int old_parent_cb = 0;
-		int successor_parent_cb = 0;
 
 		node = node->rb_right;
 		while ((left = node->rb_left) != NULL)
 			node = left;
 
 		if (rb_parent(old)) {
-			old_parent_cb = 1;
 			if (rb_parent(old)->rb_left == old)
 				rb_parent(old)->rb_left = node;
 			else
@@ -263,10 +247,8 @@ void rb_erase(struct rb_node *node, stru
 		if (parent == old) {
 			parent = node;
 		} else {
-			successor_parent_cb = 1;
 			if (child)
 				rb_set_parent(child, parent);
-
 			parent->rb_left = child;
 
 			node->rb_right = old->rb_right;
@@ -277,24 +259,6 @@ void rb_erase(struct rb_node *node, stru
 		node->rb_left = old->rb_left;
 		rb_set_parent(old->rb_left, node);
 
-		if (root->augment_cb) {
-			/*
-			 * Here, three different nodes can have new children.
-			 * The parent of the successor node that was selected
-			 * to replace the node to be erased.
-			 * The node that is getting erased and is now replaced
-			 * by its successor.
-			 * The parent of the node getting erased-replaced.
-			 */
-			if (successor_parent_cb)
-				root->augment_cb(parent);
-
-			root->augment_cb(node);
-
-			if (old_parent_cb)
-				root->augment_cb(rb_parent(old));
-		}
-
 		goto color;
 	}
 
@@ -303,19 +267,15 @@ void rb_erase(struct rb_node *node, stru
 
 	if (child)
 		rb_set_parent(child, parent);
-
-	if (parent) {
+	if (parent)
+	{
 		if (parent->rb_left == node)
 			parent->rb_left = child;
 		else
 			parent->rb_right = child;
-
-		if (root->augment_cb)
-			root->augment_cb(parent);
-
-	} else {
-		root->rb_node = child;
 	}
+	else
+		root->rb_node = child;
 
  color:
 	if (color == RB_BLACK)
@@ -323,6 +283,74 @@ void rb_erase(struct rb_node *node, stru
 }
 EXPORT_SYMBOL(rb_erase);
 
+static void rb_augment_path(struct rb_node *node, rb_augment_f func, void *data)
+{
+	struct rb_node *parent;
+
+up:
+	func(node, data);
+	parent = rb_parent(node);
+	if (!parent)
+		return;
+
+	if (node == parent->rb_left && parent->rb_right)
+		func(parent->rb_right, data);
+	else if (parent->rb_left)
+		func(parent->rb_left, data);
+
+	node = parent;
+	goto up;
+}
+
+/*
+ * after inserting @node into the tree, update the tree to account for
+ * both the new entry and any damage done by rebalance
+ */
+void rb_augment_insert(struct rb_node *node, rb_augment_f func, void *data)
+{
+	if (node->rb_left)
+		node = node->rb_left;
+	else if (node->rb_right)
+		node = node->rb_right;
+
+	rb_augment_path(node, func, data);
+}
+
+/*
+ * before removing the node, find the deepest node on the rebalance path
+ * that will still be there after @node gets removed
+ */
+struct rb_node *rb_augment_erase_begin(struct rb_node *node)
+{
+	struct rb_node *deepest;
+
+	if (!node->rb_right && !node->rb_left)
+		deepest = rb_parent(node);
+	else if (!node->rb_right)
+		deepest = node->rb_left;
+	else if (!node->rb_left)
+		deepest = node->rb_right;
+	else {
+		deepest = rb_next(node);
+		if (deepest->rb_right)
+			deepest = deepest->rb_right;
+		else if (rb_parent(deepest) != node)
+			deepest = rb_parent(deepest);
+	}
+
+	return deepest;
+}
+
+/*
+ * after removal, update the tree to account for the removed entry
+ * and any rebalance damage.
+ */
+void rb_augment_erase_end(struct rb_node *node, rb_augment_f func, void *data)
+{
+	if (node)
+		rb_augment_path(node, func, data);
+}
+
 /*
  * This function returns the first node (in sort order) of the tree.
  */

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