From 649ccb5aade8583342cdf955010ece7ad7691688 Mon Sep 17 00:00:00 2001 From: Michel Lespinasse Date: Tue, 14 Aug 2012 13:22:42 +1000 Subject: [PATCH] rbtree: adjust node color in __rb_erase_color() only when necessary In __rb_erase_color(), we were always setting a node to black after exiting the main loop. And in one case, after fixing up the tree to satisfy all rbtree invariants, we were setting the current node to root just to guarantee a loop exit, at which point the root would be set to black. However this is not necessary, as the root of an rbtree is already known to be black. The only case where the color flip is required is when we exit the loop due to the current node being red, and it's easiest to just do the flip at that point instead of doing it after the loop. Signed-off-by: Michel Lespinasse Cc: Andrea Arcangeli Acked-by: David Woodhouse Cc: Rik van Riel Cc: Peter Zijlstra Cc: Daniel Santos Cc: Jens Axboe Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton --- lib/rbtree.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/lib/rbtree.c b/lib/rbtree.c index 41cf19b2fe51..baf7c835c57c 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -259,10 +259,22 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, { struct rb_node *other; - while ((!node || rb_is_black(node)) && node != root->rb_node) - { - if (parent->rb_left == node) - { + while (true) { + /* + * Loop invariant: all leaf paths going through node have a + * black node count that is 1 lower than other leaf paths. + * + * If node is red, we can flip it to black to adjust. + * If node is the root, all leaf paths go through it. + * Otherwise, we need to adjust the tree through color flips + * and tree rotations as per one of the 4 cases below. + */ + if (node && rb_is_red(node)) { + rb_set_black(node); + break; + } else if (!parent) { + break; + } else if (parent->rb_left == node) { other = parent->rb_right; if (rb_is_red(other)) { @@ -291,12 +303,9 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, rb_set_black(parent); rb_set_black(other->rb_right); __rb_rotate_left(parent, root); - node = root->rb_node; break; } - } - else - { + } else { other = parent->rb_left; if (rb_is_red(other)) { @@ -325,13 +334,10 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent, rb_set_black(parent); rb_set_black(other->rb_left); __rb_rotate_right(parent, root); - node = root->rb_node; break; } } } - if (node) - rb_set_black(node); } void rb_erase(struct rb_node *node, struct rb_root *root) -- 2.39.5