Commit 1f052865 authored Oct 08, 2012 by Michel Lespinasse Committed by Linus Torvalds Oct 09, 2012

rbtree: break out of rb_insert_color loop after tree rotation



It is a well known property of rbtrees that insertion never requires more
than two tree rotations.  In our implementation, after one loop iteration
identified one or two necessary tree rotations, we would iterate and look
for more.  However at that point the node's parent would always be black,
which would cause us to exit the loop.

We can make the code flow more obvious by just adding a break statement
after the tree rotations, where we know we are done.  Additionally, in the
cases where two tree rotations are necessary, we don't have to update the
'node' pointer as it wouldn't be used until the next loop iteration, which
we now avoid due to this break statement.

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>

parent 910a742d

lib/rbtree.c

+4 −10

Original line number	Diff line number	Diff line
		@@ -109,18 +109,15 @@ void rb_insert_color(struct rb_node node, struct rb_root root)
		}
		}

		if (parent->rb_right == node)
		{
		register struct rb_node *tmp;
		if (parent->rb_right == node) {
		__rb_rotate_left(parent, root);
		tmp = parent;
		parent = node;
		node = tmp;
		}

		rb_set_black(parent);
		rb_set_red(gparent);
		__rb_rotate_right(gparent, root);
		break;
		} else {
		{
		register struct rb_node *uncle = gparent->rb_left;
		@@ -134,18 +131,15 @@ void rb_insert_color(struct rb_node node, struct rb_root root)
		}
		}

		if (parent->rb_left == node)
		{
		register struct rb_node *tmp;
		if (parent->rb_left == node) {
		__rb_rotate_right(parent, root);
		tmp = parent;
		parent = node;
		node = tmp;
		}

		rb_set_black(parent);
		rb_set_red(gparent);
		__rb_rotate_left(gparent, root);
		break;
		}
		}