Commit 4f035ad6 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

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: default avatarMichel Lespinasse <walken@google.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 46b6135a

lib/rbtree.c

+64 −34
Original line number Diff line number Diff line
@@ -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 +393,75 @@ 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);

		}



		if (child) {

			rb_set_parent_color(child, parent, RB_BLACK);

			/*

			 * Case 3: node's successor is leftmost under

			 * node's 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);

		}



		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)

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