From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754879Ab2GIXgD (ORCPT ); Mon, 9 Jul 2012 19:36:03 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:38226 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754825Ab2GIXf4 (ORCPT ); Mon, 9 Jul 2012 19:35:56 -0400 From: Michel Lespinasse To: aarcange@redhat.com, dwmw2@infradead.org, riel@redhat.com, peterz@infradead.org, daniel.santos@pobox.com, axboe@kernel.dk, ebiederm@xmission.com Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org Subject: [PATCH 10/13] rbtree: adjust node color in __rb_erase_color() only when necessary Date: Mon, 9 Jul 2012 16:35:20 -0700 Message-Id: <1341876923-12469-11-git-send-email-walken@google.com> X-Mailer: git-send-email 1.7.7.3 In-Reply-To: <1341876923-12469-1-git-send-email-walken@google.com> References: <1341876923-12469-1-git-send-email-walken@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- lib/rbtree.c | 28 +++++++++++++++++----------- 1 files changed, 17 insertions(+), 11 deletions(-) diff --git a/lib/rbtree.c b/lib/rbtree.c index 56369d8..44cbbd5 100644 --- a/lib/rbtree.c +++ b/lib/rbtree.c @@ -209,10 +209,22 @@ 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)) { @@ -241,12 +253,9 @@ 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)) { @@ -275,13 +284,10 @@ 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) -- 1.7.7.3