From: Michel Lespinasse <walken@google.com> 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 [thread overview] Message-ID: <1341876923-12469-11-git-send-email-walken@google.com> (raw) In-Reply-To: <1341876923-12469-1-git-send-email-walken@google.com> 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 <walken@google.com> --- 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
WARNING: multiple messages have this Message-ID (diff)
From: Michel Lespinasse <walken@google.com> 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 [thread overview] Message-ID: <1341876923-12469-11-git-send-email-walken@google.com> (raw) In-Reply-To: <1341876923-12469-1-git-send-email-walken@google.com> 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 <walken@google.com> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2012-07-09 23:36 UTC|newest] Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-07-09 23:35 [PATCH 00/13] rbtree updates Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 01/13] rbtree: reference Documentation/rbtree.txt for usage instructions Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-10 1:45 ` Rik van Riel 2012-07-10 1:45 ` Rik van Riel 2012-07-09 23:35 ` [PATCH 02/13] rbtree: empty nodes have no color Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-10 10:59 ` Daniel Santos 2012-07-10 10:59 ` Daniel Santos 2012-07-10 23:10 ` Michel Lespinasse 2012-07-10 23:10 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 03/13] rbtree: fix incorrect rbtree node insertion in fs/proc/proc_sysctl.c Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 04/13] rbtree: move some implementation details from rbtree.h to rbtree.c Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-10 12:19 ` Michal Nazarewicz 2012-07-10 12:19 ` Michal Nazarewicz 2012-07-10 23:12 ` Michel Lespinasse 2012-07-10 23:12 ` Michel Lespinasse 2012-07-11 15:48 ` Michal Nazarewicz 2012-07-11 15:48 ` Michal Nazarewicz 2012-07-09 23:35 ` [PATCH 05/13] rbtree: performance and correctness test Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-10 12:27 ` Michal Nazarewicz 2012-07-10 12:27 ` Michal Nazarewicz 2012-07-10 23:18 ` Michel Lespinasse 2012-07-10 23:18 ` Michel Lespinasse 2012-07-11 6:14 ` Michel Lespinasse 2012-07-11 6:14 ` Michel Lespinasse 2012-07-11 19:30 ` Daniel Santos 2012-07-11 19:30 ` Daniel Santos 2012-07-09 23:35 ` [PATCH 06/13] rbtree: break out of rb_insert_color loop after tree rotation Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 07/13] rbtree: adjust root color in rb_insert_color() only when necessary Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 08/13] rbtree: optimize tree rotations in rb_insert_color() Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 09/13] rbtree: optimize color flips and parent fetching " Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse [this message] 2012-07-09 23:35 ` [PATCH 10/13] rbtree: adjust node color in __rb_erase_color() only when necessary Michel Lespinasse 2012-07-09 23:35 ` [PATCH 11/13] rbtree: optimize case selection logic in __rb_erase_color() Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 12/13] rbtree: optimize tree rotations " Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-09 23:35 ` [PATCH 13/13] rbtree: optimize color flips " Michel Lespinasse 2012-07-09 23:35 ` Michel Lespinasse 2012-07-11 13:23 ` [PATCH 00/13] rbtree updates Peter Zijlstra 2012-07-11 13:23 ` Peter Zijlstra 2012-07-12 1:12 ` Michel Lespinasse 2012-07-12 1:12 ` Michel Lespinasse 2012-07-12 14:09 ` Peter Zijlstra 2012-07-12 14:09 ` Peter Zijlstra 2012-07-12 14:12 ` Peter Zijlstra 2012-07-12 14:12 ` Peter Zijlstra 2012-07-13 0:39 ` Michel Lespinasse 2012-07-13 0:39 ` Michel Lespinasse
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