rbtree: optimize fetching of sibling node

When looking to fetch a node's sibling, we went through a sequence of:
- check if node is the parent's left child
- if it is, then fetch the parent's right child

This can be replaced with:
- fetch the parent's right child as an assumed sibling
- check that node is NOT the fetched child

This avoids fetching the parent's left child when node is actually
that child. Saves a bit on code size, though it doesn't seem to make
a large difference in speed.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/lib/rbtree.c b/lib/rbtree.c
index 08926709b4f9..61cdd0e3e538 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -107,8 +107,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
 
                 gparent = rb_red_parent(parent);
 
-                if (parent == gparent->rb_left) {
-                        tmp = gparent->rb_right;
+                tmp = gparent->rb_right;
+                if (parent != tmp) {    /* parent == gparent->rb_left */
                         if (tmp && rb_is_red(tmp)) {
                                 /*
                                  * Case 1 - color flips
@@ -131,7 +131,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                 continue;
                         }
 
-                        if (parent->rb_right == node) {
+                        tmp = parent->rb_right;
+                        if (node == tmp) {
                                 /*
                                  * Case 2 - left rotate at parent
                                  *
@@ -151,6 +152,7 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                                             RB_BLACK);
                                 rb_set_parent_color(parent, node, RB_RED);
                                 parent = node;
+                                tmp = node->rb_right;
                         }
 
                         /*
@@ -162,7 +164,7 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                          *     /                 \
                          *    n                   U
                          */
-                        gparent->rb_left = tmp = parent->rb_right;
+                        gparent->rb_left = tmp;  /* == parent->rb_right */
                         parent->rb_right = gparent;
                         if (tmp)
                                 rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -180,7 +182,8 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                 continue;
                         }
 
-                        if (parent->rb_left == node) {
+                        tmp = parent->rb_left;
+                        if (node == tmp) {
                                 /* Case 2 - right rotate at parent */
                                 parent->rb_left = tmp = node->rb_right;
                                 node->rb_right = parent;
@@ -189,10 +192,11 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                                             RB_BLACK);
                                 rb_set_parent_color(parent, node, RB_RED);
                                 parent = node;
+                                tmp = node->rb_left;
                         }
 
                         /* Case 3 - left rotate at gparent */
-                        gparent->rb_right = tmp = parent->rb_left;
+                        gparent->rb_right = tmp;  /* == parent->rb_left */
                         parent->rb_left = gparent;
                         if (tmp)
                                 rb_set_parent_color(tmp, gparent, RB_BLACK);
@@ -223,8 +227,9 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
                         break;
                 } else if (!parent) {
                         break;
-                } else if (parent->rb_left == node) {
-                        sibling = parent->rb_right;
+                }
+                sibling = parent->rb_right;
+                if (node != sibling) {  /* node == parent->rb_left */
                         if (rb_is_red(sibling)) {
                                 /*
                                  * Case 1 - left rotate at parent