linux-kernel - [PATCH 13/13] rbtree: optimize color flips in __rb_erase

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Date:	Mon,  9 Jul 2012 16:35:23 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	aarcange@...hat.com, dwmw2@...radead.org, riel@...hat.com,
	peterz@...radead.org, daniel.santos@...ox.com, axboe@...nel.dk,
	ebiederm@...ssion.com
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: [PATCH 13/13] rbtree: optimize color flips in __rb_erase_color()

In __rb_erase_color(), when the current node is red or when flipping
the sibling's color, the parent is already known so we can use the
more efficient rb_set_parent_color() function to set the desired color.

Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
 lib/rbtree.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index c956248..f8c1a75 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -29,8 +29,6 @@
 #define rb_color(r)   ((r)->rb_parent_color & 1)
 #define rb_is_red(r)   (!rb_color(r))
 #define rb_is_black(r) rb_color(r)
-#define rb_set_red(r)  do { (r)->rb_parent_color &= ~1; } while (0)
-#define rb_set_black(r)  do { (r)->rb_parent_color |= 1; } while (0)
 
 static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
 {
@@ -170,7 +168,7 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 		 * and tree rotations as per one of the 4 cases below.
 		 */
 		if (node && rb_is_red(node)) {
-			rb_set_black(node);
+			rb_set_parent_color(node, parent, RB_BLACK);
 			break;
 		} else if (!parent) {
 			break;
@@ -190,7 +188,8 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 				tmp2 = sibling->rb_left;
 				if (!tmp2 || rb_is_black(tmp2)) {
 					/* Case 2 - sibling color flip */
-					rb_set_red(sibling);
+					rb_set_parent_color(sibling, parent,
+							    RB_RED);
 					node = parent;
 					parent = rb_parent(node);
 					continue;
@@ -230,7 +229,8 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 				tmp2 = sibling->rb_right;
 				if (!tmp2 || rb_is_black(tmp2)) {
 					/* Case 2 - sibling color flip */
-					rb_set_red(sibling);
+					rb_set_parent_color(sibling, parent,
+							    RB_RED);
 					node = parent;
 					parent = rb_parent(node);
 					continue;
-- 
1.7.7.3

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