rbtree: optimize case selection logic in __rb_erase_color() (e125d147) · Commits · 戴 / test

In __rb_erase_color(), we have to select one of 3 cases depending on the color on the 'other' node children. If both children are black, we flip a few node colors and iterate. Otherwise, we do either one or two tree rotations, depending on the color of the 'other' child opposite to 'node', and then we are done. The corresponding logic had duplicate checks for the color of the 'other' child opposite to 'node'. It was checking it first to determine if both children are black, and then to determine how many tree rotations are required. Rearrange the logic to avoid that extra check. Signed-off-by:

Michel Lespinasse <walken@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Acked-by:

David 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

lib/rbtree.c

+30 −38

Original line number	Diff line number	Diff line
		@@ -283,17 +283,14 @@ static void __rb_erase_color(struct rb_node node, struct rb_node parent,
		__rb_rotate_left(parent, root);
		other = parent->rb_right;
		}
		if ((!other->rb_left \|\| rb_is_black(other->rb_left)) &&
		(!other->rb_right \|\| rb_is_black(other->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);
		node = parent;
		parent = rb_parent(node);
		continue;
		}
		else
		{
		if (!other->rb_right \|\| rb_is_black(other->rb_right))
		{
		rb_set_black(other->rb_left);
		rb_set_red(other);
		__rb_rotate_right(other, root);
		@@ -304,7 +301,6 @@ static void __rb_erase_color(struct rb_node node, struct rb_node parent,
		rb_set_black(other->rb_right);
		__rb_rotate_left(parent, root);
		break;
		}
		} else {
		other = parent->rb_left;
		if (rb_is_red(other))
		@@ -314,17 +310,14 @@ static void __rb_erase_color(struct rb_node node, struct rb_node parent,
		__rb_rotate_right(parent, root);
		other = parent->rb_left;
		}
		if ((!other->rb_left \|\| rb_is_black(other->rb_left)) &&
		(!other->rb_right \|\| rb_is_black(other->rb_right)))
		{
		if (!other->rb_left \|\| rb_is_black(other->rb_left)) {
		if (!other->rb_right \|\|
		rb_is_black(other->rb_right)) {
		rb_set_red(other);
		node = parent;
		parent = rb_parent(node);
		continue;
		}
		else
		{
		if (!other->rb_left \|\| rb_is_black(other->rb_left))
		{
		rb_set_black(other->rb_right);
		rb_set_red(other);
		__rb_rotate_left(other, root);
		@@ -338,7 +331,6 @@ static void __rb_erase_color(struct rb_node node, struct rb_node parent,
		}
		}
		}
		}

		void rb_erase(struct rb_node node, struct rb_root root)
		{

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