Commit 6280d235 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

rbtree: low level optimizations in __rb_erase_color() 



In __rb_erase_color(), we often already have pointers to the nodes being
rotated and/or know what their colors must be, so we can generate more
efficient code than the generic __rb_rotate_left() and __rb_rotate_right()
functions.

Also 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: default avatarMichel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: default avatarDavid 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e125d147

lib/rbtree.c

+115 −93
Original line number Diff line number Diff line
@@ -39,7 +39,8 @@ 
 *  5), then the longest possible path due to 4 is 2B.

 *

 *  We shall indicate color with case, where black nodes are uppercase and red

 *  nodes will be lowercase.

 *  nodes will be lowercase. Unknown color nodes shall be drawn as red within

 *  parentheses and have some accompanying text comment.

 */



#define	RB_RED		0
@@ -48,17 +49,11 @@ 
#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)

{

	rb->__rb_parent_color = rb_color(rb) | (unsigned long)p;

}

static inline void rb_set_color(struct rb_node *rb, int color)

{

	rb->__rb_parent_color = (rb->__rb_parent_color & ~1) | color;

}



static inline void rb_set_parent_color(struct rb_node *rb,

				       struct rb_node *p, int color)
@@ -71,52 +66,6 @@ static inline struct rb_node *rb_red_parent(struct rb_node *red) 
	return (struct rb_node *)red->__rb_parent_color;

}



static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)

{

	struct rb_node *right = node->rb_right;

	struct rb_node *parent = rb_parent(node);



	if ((node->rb_right = right->rb_left))

		rb_set_parent(right->rb_left, node);

	right->rb_left = node;



	rb_set_parent(right, parent);



	if (parent)

	{

		if (node == parent->rb_left)

			parent->rb_left = right;

		else

			parent->rb_right = right;

	}

	else

		root->rb_node = right;

	rb_set_parent(node, right);

}



static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)

{

	struct rb_node *left = node->rb_left;

	struct rb_node *parent = rb_parent(node);



	if ((node->rb_left = left->rb_right))

		rb_set_parent(left->rb_right, node);

	left->rb_right = node;



	rb_set_parent(left, parent);



	if (parent)

	{

		if (node == parent->rb_right)

			parent->rb_right = left;

		else

			parent->rb_left = left;

	}

	else

		root->rb_node = left;

	rb_set_parent(node, left);

}



/*

 * Helper function for rotations:

 * - old's parent and color get assigned to new
@@ -257,7 +206,7 @@ EXPORT_SYMBOL(rb_insert_color); 
static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,

			     struct rb_root *root)

{

	struct rb_node *other;

	struct rb_node *sibling, *tmp1, *tmp2;



	while (true) {

		/*
@@ -270,63 +219,136 @@ 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;

		} else if (parent->rb_left == node) {

			other = parent->rb_right;

			if (rb_is_red(other))

			{

				rb_set_black(other);

				rb_set_red(parent);

				__rb_rotate_left(parent, root);

				other = parent->rb_right;

			}

			if (!other->rb_right || rb_is_black(other->rb_right)) {

				if (!other->rb_left ||

				    rb_is_black(other->rb_left)) {

					rb_set_red(other);

			sibling = parent->rb_right;

			if (rb_is_red(sibling)) {

				/*

				 * Case 1 - left rotate at parent

				 *

				 *     P               S

				 *    / \             / \

				 *   N   s    -->    p   Sr

				 *      / \         / \

				 *     Sl  Sr      N   Sl

				 */

				parent->rb_right = tmp1 = sibling->rb_left;

				sibling->rb_left = parent;

				rb_set_parent_color(tmp1, parent, RB_BLACK);

				__rb_rotate_set_parents(parent, sibling, root,

							RB_RED);

				sibling = tmp1;

			}

			tmp1 = sibling->rb_right;

			if (!tmp1 || rb_is_black(tmp1)) {

				tmp2 = sibling->rb_left;

				if (!tmp2 || rb_is_black(tmp2)) {

					/*

					 * Case 2 - sibling color flip

					 * (p could be either color here)

					 *

					 *    (p)           (p)

					 *    / \           / \

					 *   N   S    -->  N   s

					 *      / \           / \

					 *     Sl  Sr        Sl  Sr

					 *

					 * This leaves us violating 5), so

					 * recurse at p. If p is red, the

					 * recursion will just flip it to black

					 * and exit. If coming from Case 1,

					 * p is known to be red.

					 */

					rb_set_parent_color(sibling, parent,

							    RB_RED);

					node = parent;

					parent = rb_parent(node);

					continue;

				}

				rb_set_black(other->rb_left);

				rb_set_red(other);

				__rb_rotate_right(other, root);

				other = parent->rb_right;

				/*

				 * Case 3 - right rotate at sibling

				 * (p could be either color here)

				 *

				 *   (p)           (p)

				 *   / \           / \

				 *  N   S    -->  N   Sl

				 *     / \             \

				 *    sl  Sr            s

				 *                       \

				 *                        Sr

				 */

				sibling->rb_left = tmp1 = tmp2->rb_right;

				tmp2->rb_right = sibling;

				parent->rb_right = tmp2;

				if (tmp1)

					rb_set_parent_color(tmp1, sibling,

							    RB_BLACK);

				tmp1 = sibling;

				sibling = tmp2;

			}

			rb_set_color(other, rb_color(parent));

			rb_set_black(parent);

			rb_set_black(other->rb_right);

			__rb_rotate_left(parent, root);

			/*

			 * Case 4 - left rotate at parent + color flips

			 * (p and sl could be either color here.

			 *  After rotation, p becomes black, s acquires

			 *  p's color, and sl keeps its color)

			 *

			 *      (p)             (s)

			 *      / \             / \

			 *     N   S     -->   P   Sr

			 *        / \         / \

			 *      (sl) sr      N  (sl)

			 */

			parent->rb_right = tmp2 = sibling->rb_left;

			sibling->rb_left = parent;

			rb_set_parent_color(tmp1, sibling, RB_BLACK);

			if (tmp2)

				rb_set_parent(tmp2, parent);

			__rb_rotate_set_parents(parent, sibling, root,

						RB_BLACK);

			break;

		} else {

			other = parent->rb_left;

			if (rb_is_red(other))

			{

				rb_set_black(other);

				rb_set_red(parent);

				__rb_rotate_right(parent, root);

				other = parent->rb_left;

			}

			if (!other->rb_left || rb_is_black(other->rb_left)) {

				if (!other->rb_right ||

				    rb_is_black(other->rb_right)) {

					rb_set_red(other);

			sibling = parent->rb_left;

			if (rb_is_red(sibling)) {

				/* Case 1 - right rotate at parent */

				parent->rb_left = tmp1 = sibling->rb_right;

				sibling->rb_right = parent;

				rb_set_parent_color(tmp1, parent, RB_BLACK);

				__rb_rotate_set_parents(parent, sibling, root,

							RB_RED);

				sibling = tmp1;

			}

			tmp1 = sibling->rb_left;

			if (!tmp1 || rb_is_black(tmp1)) {

				tmp2 = sibling->rb_right;

				if (!tmp2 || rb_is_black(tmp2)) {

					/* Case 2 - sibling color flip */

					rb_set_parent_color(sibling, parent,

							    RB_RED);

					node = parent;

					parent = rb_parent(node);

					continue;

				}

				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);

				/* Case 3 - right rotate at sibling */

				sibling->rb_right = tmp1 = tmp2->rb_left;

				tmp2->rb_left = sibling;

				parent->rb_left = tmp2;

				if (tmp1)

					rb_set_parent_color(tmp1, sibling,

							    RB_BLACK);

				tmp1 = sibling;

				sibling = tmp2;

			}

			/* Case 4 - left rotate at parent + color flips */

			parent->rb_left = tmp2 = sibling->rb_right;

			sibling->rb_right = parent;

			rb_set_parent_color(tmp1, sibling, RB_BLACK);

			if (tmp2)

				rb_set_parent(tmp2, parent);

			__rb_rotate_set_parents(parent, sibling, root,

						RB_BLACK);

			break;

		}

	}

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