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Message-Id: <1343946858-8170-7-git-send-email-walken@google.com>
Date: Thu, 2 Aug 2012 15:34:15 -0700
From: Michel Lespinasse <walken@...gle.com>
To: riel@...hat.com, peterz@...radead.org, daniel.santos@...ox.com,
aarcange@...hat.com, dwmw2@...radead.org, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
torvalds@...ux-foundation.org
Subject: [PATCH v2 6/9] rbtree: low level optimizations in rb_erase()
Various minor optimizations in rb_erase():
- Avoid multiple loading of node->__rb_parent_color when computing parent
and color information (possibly not in close sequence, as there might
be further branches in the algorithm)
- In the 1-child subcase of case 1, copy the __rb_parent_color field from
the erased node to the child instead of recomputing it from the desired
parent and color
- When searching for the erased node's successor, differentiate between
cases 2 and 3 based on whether any left links were followed. This avoids
a condition later down.
- In case 3, keep a pointer to the erased node's right child so we don't
have to refetch it later to adjust its parent.
- In the no-childs subcase of cases 2 and 3, place the rebalance assigment
last so that the compiler can remove the following if(rebalance) test.
Also, added some comments to illustrate cases 2 and 3.
Signed-off-by: Michel Lespinasse <walken@...gle.com>
---
lib/rbtree.c | 97 +++++++++++++++++++++++++++++++++++++--------------------
1 files changed, 63 insertions(+), 34 deletions(-)
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 80b0925..12d9147 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -47,9 +47,14 @@
#define RB_RED 0
#define RB_BLACK 1
-#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_parent(pc) ((struct rb_node *)(pc & ~3))
+
+#define __rb_color(pc) ((pc) & 1)
+#define __rb_is_black(pc) __rb_color(pc)
+#define __rb_is_red(pc) (!__rb_color(pc))
+#define rb_color(rb) __rb_color((rb)->__rb_parent_color)
+#define rb_is_red(rb) __rb_is_red((rb)->__rb_parent_color)
+#define rb_is_black(rb) __rb_is_black((rb)->__rb_parent_color)
static inline void rb_set_black(struct rb_node *rb)
{
@@ -378,6 +383,7 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
{
struct rb_node *child = node->rb_right, *tmp = node->rb_left;
struct rb_node *parent, *rebalance;
+ unsigned long pc;
if (!tmp) {
/*
@@ -387,51 +393,74 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
* and node must be black due to 4). We adjust colors locally
* so as to bypass __rb_erase_color() later on.
*/
-
- parent = rb_parent(node);
+ pc = node->__rb_parent_color;
+ parent = __rb_parent(pc);
__rb_change_child(node, child, parent, root);
if (child) {
- rb_set_parent_color(child, parent, RB_BLACK);
+ child->__rb_parent_color = pc;
rebalance = NULL;
- } else {
- rebalance = rb_is_black(node) ? parent : NULL;
- }
+ } else
+ rebalance = __rb_is_black(pc) ? parent : NULL;
} else if (!child) {
/* Still case 1, but this time the child is node->rb_left */
- parent = rb_parent(node);
+ tmp->__rb_parent_color = pc = node->__rb_parent_color;
+ parent = __rb_parent(pc);
__rb_change_child(node, tmp, parent, root);
- rb_set_parent_color(tmp, parent, RB_BLACK);
rebalance = NULL;
} else {
- struct rb_node *old = node, *left;
-
- node = child;
- while ((left = node->rb_left) != NULL)
- node = left;
-
- __rb_change_child(old, node, rb_parent(old), root);
-
- child = node->rb_right;
- parent = rb_parent(node);
-
- if (parent == old) {
- parent = node;
+ struct rb_node *successor = child, *child2;
+ tmp = child->rb_left;
+ if (!tmp) {
+ /*
+ * Case 2: node's successor is its right child
+ *
+ * (n) (s)
+ * / \ / \
+ * (x) (s) -> (x) (c)
+ * \
+ * (c)
+ */
+ parent = child;
+ child2 = child->rb_right;
} else {
- parent->rb_left = child;
-
- node->rb_right = old->rb_right;
- rb_set_parent(old->rb_right, node);
+ /* Case 3: node's successor is leftmost under its
+ * right child subtree
+ *
+ * (n) (s)
+ * / \ / \
+ * (x) (y) -> (x) (y)
+ * / /
+ * (p) (p)
+ * / /
+ * (s) (c)
+ * \
+ * (c)
+ */
+ do {
+ parent = successor;
+ successor = tmp;
+ tmp = tmp->rb_left;
+ } while (tmp);
+ parent->rb_left = child2 = successor->rb_right;
+ successor->rb_right = child;
+ rb_set_parent(child, successor);
}
- if (child) {
- rb_set_parent_color(child, parent, RB_BLACK);
+ successor->rb_left = tmp = node->rb_left;
+ rb_set_parent(tmp, successor);
+
+ pc = node->__rb_parent_color;
+ tmp = __rb_parent(pc);
+ __rb_change_child(node, successor, tmp, root);
+ if (child2) {
+ successor->__rb_parent_color = pc;
+ rb_set_parent_color(child2, parent, RB_BLACK);
rebalance = NULL;
} else {
- rebalance = rb_is_black(node) ? parent : NULL;
+ unsigned long pc2 = successor->__rb_parent_color;
+ successor->__rb_parent_color = pc;
+ rebalance = __rb_is_black(pc2) ? parent : NULL;
}
- node->__rb_parent_color = old->__rb_parent_color;
- node->rb_left = old->rb_left;
- rb_set_parent(old->rb_left, node);
}
if (rebalance)
--
1.7.7.3
--
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