From ed35a6bcfc2386477ab1470e5780ad9f1863c701 Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <walken@google.com>
Date: Tue, 14 Aug 2012 13:22:42 +1000
Subject: [PATCH] rbtree: optimize case selection logic in __rb_erase_color()

In __rb_erase_color(), we have to select one of 3 cases depending on the
color on the 'other' node children.  If both children are black, we flip a
few node colors and iterate.  Otherwise, we do either one or two tree
rotations, depending on the color of the 'other' child opposite to 'node',
and then we are done.

The corresponding logic had duplicate checks for the color of the 'other'
child opposite to 'node'.  It was checking it first to determine if both
children are black, and then to determine how many tree rotations are
required.  Rearrange the logic to avoid that extra check.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 lib/rbtree.c | 68 +++++++++++++++++++++++-----------------------------
 1 file changed, 30 insertions(+), 38 deletions(-)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index baf7c835c57c..eb823a31099c 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -283,28 +283,24 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 				__rb_rotate_left(parent, root);
 				other = parent->rb_right;
 			}
-			if ((!other->rb_left || rb_is_black(other->rb_left)) &&
-			    (!other->rb_right || rb_is_black(other->rb_right)))
-			{
-				rb_set_red(other);
-				node = parent;
-				parent = rb_parent(node);
-			}
-			else
-			{
-				if (!other->rb_right || rb_is_black(other->rb_right))
-				{
-					rb_set_black(other->rb_left);
+			if (!other->rb_right || rb_is_black(other->rb_right)) {
+				if (!other->rb_left ||
+				    rb_is_black(other->rb_left)) {
 					rb_set_red(other);
-					__rb_rotate_right(other, root);
-					other = parent->rb_right;
+					node = parent;
+					parent = rb_parent(node);
+					continue;
 				}
-				rb_set_color(other, rb_color(parent));
-				rb_set_black(parent);
-				rb_set_black(other->rb_right);
-				__rb_rotate_left(parent, root);
-				break;
+				rb_set_black(other->rb_left);
+				rb_set_red(other);
+				__rb_rotate_right(other, root);
+				other = parent->rb_right;
 			}
+			rb_set_color(other, rb_color(parent));
+			rb_set_black(parent);
+			rb_set_black(other->rb_right);
+			__rb_rotate_left(parent, root);
+			break;
 		} else {
 			other = parent->rb_left;
 			if (rb_is_red(other))
@@ -314,28 +310,24 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 				__rb_rotate_right(parent, root);
 				other = parent->rb_left;
 			}
-			if ((!other->rb_left || rb_is_black(other->rb_left)) &&
-			    (!other->rb_right || rb_is_black(other->rb_right)))
-			{
-				rb_set_red(other);
-				node = parent;
-				parent = rb_parent(node);
-			}
-			else
-			{
-				if (!other->rb_left || rb_is_black(other->rb_left))
-				{
-					rb_set_black(other->rb_right);
+			if (!other->rb_left || rb_is_black(other->rb_left)) {
+				if (!other->rb_right ||
+				    rb_is_black(other->rb_right)) {
 					rb_set_red(other);
-					__rb_rotate_left(other, root);
-					other = parent->rb_left;
+					node = parent;
+					parent = rb_parent(node);
+					continue;
 				}
-				rb_set_color(other, rb_color(parent));
-				rb_set_black(parent);
-				rb_set_black(other->rb_left);
-				__rb_rotate_right(parent, root);
-				break;
+				rb_set_black(other->rb_right);
+				rb_set_red(other);
+				__rb_rotate_left(other, root);
+				other = parent->rb_left;
 			}
+			rb_set_color(other, rb_color(parent));
+			rb_set_black(parent);
+			rb_set_black(other->rb_left);
+			__rb_rotate_right(parent, root);
+			break;
 		}
 	}
 }
-- 
2.39.5