rbtree: empty nodes have no color

Empty nodes have no color.  We can make use of this property to simplify
the code emitted by the RB_EMPTY_NODE and RB_CLEAR_NODE macros.  Also, we
can get rid of the rb_init_node function which had been introduced by
88d19cf37952 ("timers: Add rb_init_node() to allow for stack allocated rb
nodes") to avoid some issue with the empty node's color not being
initialized.

I'm not sure what the RB_EMPTY_NODE checks in rb_prev() / rb_next() are
doing there, though.  axboe introduced them in 10fd48f2376d ("rbtree:
fixed reversed RB_EMPTY_NODE and rb_next/prev").  The way I see it, the
'empty node' abstraction is only used by rbtree users to flag nodes that
they haven't inserted in any rbtree, so asking the predecessor or
successor of such nodes doesn't make any sense.

One final rb_init_node() caller was recently added in sysctl code to
implement faster sysctl name lookups.  This code doesn't make use of
RB_EMPTY_NODE at all, and from what I could see it only called
rb_init_node() under the mistaken assumption that such initialization was
required before node insertion.

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>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index eb7cc91b7258870f89b77a60de4172dd6f1502b6..080855bb6b7443fad0d096bc02f960f7415f540b 100644 (file)
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -168,10 +168,8 @@ static void init_header(struct ctl_table_header *head,
        head->node = node;
        if (node) {
                struct ctl_table *entry;
-               for (entry = table; entry->procname; entry++, node++) {
-                       rb_init_node(&node->node);
+               for (entry = table; entry->procname; entry++, node++)
                        node->header = head;
-               }
        }
 }
 

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index e6a807720ded441c8b26c371432bb3b318f2fcac..2049087c43b74b2105f5cf4138f2fbcad50dbca5 100644 (file)
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -67,17 +67,12 @@ static inline void rb_set_color(struct rb_node *rb, int color)
 #define RB_ROOT        (struct rb_root) { NULL, }
 #define        rb_entry(ptr, type, member) container_of(ptr, type, member)
 
-#define RB_EMPTY_ROOT(root)    ((root)->rb_node == NULL)
-#define RB_EMPTY_NODE(node)    (rb_parent(node) == node)
-#define RB_CLEAR_NODE(node)    (rb_set_parent(node, node))
+#define RB_EMPTY_ROOT(root)  ((root)->rb_node == NULL)
+
+/* 'empty' nodes are nodes that are known not to be inserted in an rbree */
+#define RB_EMPTY_NODE(node)  ((node)->rb_parent_color == (unsigned long)(node))
+#define RB_CLEAR_NODE(node)  ((node)->rb_parent_color = (unsigned long)(node))
 
-static inline void rb_init_node(struct rb_node *rb)
-{
-       rb->rb_parent_color = 0;
-       rb->rb_right = NULL;
-       rb->rb_left = NULL;
-       RB_CLEAR_NODE(rb);
-}
 
 extern void rb_insert_color(struct rb_node *, struct rb_root *);
 extern void rb_erase(struct rb_node *, struct rb_root *);

diff --git a/include/linux/timerqueue.h b/include/linux/timerqueue.h
index 5088727478fd8ad91bc7e17f9b85252b8ef8e4a2..a520fd70a59f371f40a34f79e883dcf7b32c23f7 100644 (file)
--- a/include/linux/timerqueue.h
+++ b/include/linux/timerqueue.h
@@ -39,7 +39,7 @@ struct timerqueue_node *timerqueue_getnext(struct timerqueue_head *head)
 
 static inline void timerqueue_init(struct timerqueue_node *node)
 {
-       rb_init_node(&node->node);
+       RB_CLEAR_NODE(&node->node);
 }
 
 static inline void timerqueue_init_head(struct timerqueue_head *head)

diff --git a/lib/rbtree.c b/lib/rbtree.c
index d4175565dc2cb55e6de609a5b93ca4e3908b66b4..fe43c8c5f527e039cac44d3c22157ad4b3c2b5fd 100644 (file)
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -387,7 +387,7 @@ struct rb_node *rb_next(const struct rb_node *node)
 {
        struct rb_node *parent;
 
-       if (rb_parent(node) == node)
+       if (RB_EMPTY_NODE(node))
                return NULL;
 
        /* If we have a right-hand child, go down and then left as far
@@ -416,7 +416,7 @@ struct rb_node *rb_prev(const struct rb_node *node)
 {
        struct rb_node *parent;
 
-       if (rb_parent(node) == node)
+       if (RB_EMPTY_NODE(node))
                return NULL;
 
        /* If we have a left-hand child, go down and then right as far