[RBTREE] Merge colour and parent fields of struct rb_node.

We only used a single bit for colour information, so having a whole
machine word of space allocated for it was a bit wasteful. Instead,
store it in the lowest bit of the 'parent' pointer, since that was
always going to be aligned anyway.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

2 files changed, 109 insertions, 101 deletions

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index ffee81ce7b6f..748be50329d8 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -99,28 +99,35 @@ static inline struct page * rb_insert_page_cache(struct inode * inode,
 
 struct rb_node
 {
-        struct rb_node *rb_parent;
-        int rb_color;
+        unsigned long  rb_parent_colour;
 #define RB_RED          0
 #define RB_BLACK        1
         struct rb_node *rb_right;
         struct rb_node *rb_left;
 };
 
-#define rb_parent(r)            ((r)->rb_parent)
-#define rb_set_parent(r,p)      do { (r)->rb_parent = p; } while (0)
-#define rb_colour(r)            ((r)->rb_colour)
-#define rb_is_red(r)            ((r)->colour == RB_RED)
-#define rb_is_black(r)          ((r)->colour == RB_BLACK)
-#define rb_set_red(r)           do { (r)->colour = RB_RED; } while (0)
-#define rb_set_black(r)         do { (r)->colour = RB_BLACK; } while (0)
-#define rb_set_colour(r,c)      do { (r)->colour = (c); } while (0)
-
 struct rb_root
 {
         struct rb_node *rb_node;
 };
 
+
+#define rb_parent(r)   ((struct rb_node *)((r)->rb_parent_colour & ~3))
+#define rb_colour(r)   ((r)->rb_parent_colour & 1)
+#define rb_is_red(r)   (!rb_colour(r))
+#define rb_is_black(r) rb_colour(r)
+#define rb_set_red(r)  do { (r)->rb_parent_colour &= ~1; } while (0)
+#define rb_set_black(r)  do { (r)->rb_parent_colour |= 1; } while (0)
+
+static inline void rb_set_parent(struct rb_node *rb, struct rb_node *p)
+{
+        rb->rb_parent_colour = (rb->rb_parent_colour & 3) | (unsigned long)p;
+}
+static inline void rb_set_colour(struct rb_node *rb, int colour)
+{
+        rb->rb_parent_colour = (rb->rb_parent_colour & ~1) | colour;
+}
+
 #define RB_ROOT (struct rb_root) { NULL, }
 #define rb_entry(ptr, type, member) container_of(ptr, type, member)
 
@@ -140,8 +147,7 @@ extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
 static inline void rb_link_node(struct rb_node * node, struct rb_node * parent,
                                 struct rb_node ** rb_link)
 {
-        node->rb_parent = parent;
-        node->rb_color = RB_RED;
+        node->rb_parent_colour = (unsigned long )parent;
         node->rb_left = node->rb_right = NULL;
 
         *rb_link = node;
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 63473e04f18a..4a7173cad149 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -26,60 +26,66 @@
 static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)
 {
         struct rb_node *right = node->rb_right;
+        struct rb_node *parent = rb_parent(node);
 
         if ((node->rb_right = right->rb_left))
-                right->rb_left->rb_parent = node;
+                rb_set_parent(right->rb_left, node);
         right->rb_left = node;
 
-        if ((right->rb_parent = node->rb_parent))
+        rb_set_parent(right, parent);
+
+        if (parent)
         {
-                if (node == node->rb_parent->rb_left)
-                        node->rb_parent->rb_left = right;
+                if (node == parent->rb_left)
+                        parent->rb_left = right;
                 else
-                        node->rb_parent->rb_right = right;
+                        parent->rb_right = right;
         }
         else
                 root->rb_node = right;
-        node->rb_parent = right;
+        rb_set_parent(node, right);
 }
 
 static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
 {
         struct rb_node *left = node->rb_left;
+        struct rb_node *parent = rb_parent(node);
 
         if ((node->rb_left = left->rb_right))
-                left->rb_right->rb_parent = node;
+                rb_set_parent(left->rb_right, node);
         left->rb_right = node;
 
-        if ((left->rb_parent = node->rb_parent))
+        rb_set_parent(left, parent);
+
+        if (parent)
         {
-                if (node == node->rb_parent->rb_right)
-                        node->rb_parent->rb_right = left;
+                if (node == parent->rb_right)
+                        parent->rb_right = left;
                 else
-                        node->rb_parent->rb_left = left;
+                        parent->rb_left = left;
         }
         else
                 root->rb_node = left;
-        node->rb_parent = left;
+        rb_set_parent(node, left);
 }
 
 void rb_insert_color(struct rb_node *node, struct rb_root *root)
 {
         struct rb_node *parent, *gparent;
 
-        while ((parent = node->rb_parent) && parent->rb_color == RB_RED)
+        while ((parent = rb_parent(node)) && rb_is_red(parent))
         {
-                gparent = parent->rb_parent;
+                gparent = rb_parent(parent);
 
                 if (parent == gparent->rb_left)
                 {
                         {
                                 register struct rb_node *uncle = gparent->rb_right;
-                                if (uncle && uncle->rb_color == RB_RED)
+                                if (uncle && rb_is_red(uncle))
                                 {
-                                        uncle->rb_color = RB_BLACK;
-                                        parent->rb_color = RB_BLACK;
-                                        gparent->rb_color = RB_RED;
+                                        rb_set_black(uncle);
+                                        rb_set_black(parent);
+                                        rb_set_red(gparent);
                                         node = gparent;
                                         continue;
                                 }
@@ -94,17 +100,17 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                 node = tmp;
                         }
 
-                        parent->rb_color = RB_BLACK;
-                        gparent->rb_color = RB_RED;
+                        rb_set_black(parent);
+                        rb_set_red(gparent);
                         __rb_rotate_right(gparent, root);
                 } else {
                         {
                                 register struct rb_node *uncle = gparent->rb_left;
-                                if (uncle && uncle->rb_color == RB_RED)
+                                if (uncle && rb_is_red(uncle))
                                 {
-                                        uncle->rb_color = RB_BLACK;
-                                        parent->rb_color = RB_BLACK;
-                                        gparent->rb_color = RB_RED;
+                                        rb_set_black(uncle);
+                                        rb_set_black(parent);
+                                        rb_set_red(gparent);
                                         node = gparent;
                                         continue;
                                 }
@@ -119,13 +125,13 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
                                 node = tmp;
                         }
 
-                        parent->rb_color = RB_BLACK;
-                        gparent->rb_color = RB_RED;
+                        rb_set_black(parent);
+                        rb_set_red(gparent);
                         __rb_rotate_left(gparent, root);
                 }
         }
 
-        root->rb_node->rb_color = RB_BLACK;
+        rb_set_black(root->rb_node);
 }
 EXPORT_SYMBOL(rb_insert_color);
 
@@ -134,43 +140,40 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
 {
         struct rb_node *other;
 
-        while ((!node || node->rb_color == RB_BLACK) && node != root->rb_node)
+        while ((!node || rb_is_black(node)) && node != root->rb_node)
         {
                 if (parent->rb_left == node)
                 {
                         other = parent->rb_right;
-                        if (other->rb_color == RB_RED)
+                        if (rb_is_red(other))
                         {
-                                other->rb_color = RB_BLACK;
-                                parent->rb_color = RB_RED;
+                                rb_set_black(other);
+                                rb_set_red(parent);
                                 __rb_rotate_left(parent, root);
                                 other = parent->rb_right;
                         }
-                        if ((!other->rb_left ||
-                             other->rb_left->rb_color == RB_BLACK)
-                            && (!other->rb_right ||
-                                other->rb_right->rb_color == RB_BLACK))
+                        if ((!other->rb_left || rb_is_black(other->rb_left)) &&
+                            (!other->rb_right || rb_is_black(other->rb_right)))
                         {
-                                other->rb_color = RB_RED;
+                                rb_set_red(other);
                                 node = parent;
-                                parent = node->rb_parent;
+                                parent = rb_parent(node);
                         }
                         else
                         {
-                                if (!other->rb_right ||
-                                    other->rb_right->rb_color == RB_BLACK)
+                                if (!other->rb_right || rb_is_black(other->rb_right))
                                 {
-                                        register struct rb_node *o_left;
+                                        struct rb_node *o_left;
                                         if ((o_left = other->rb_left))
-                                                o_left->rb_color = RB_BLACK;
-                                        other->rb_color = RB_RED;
+                                                rb_set_black(o_left);
+                                        rb_set_red(other);
                                         __rb_rotate_right(other, root);
                                         other = parent->rb_right;
                                 }
-                                other->rb_color = parent->rb_color;
-                                parent->rb_color = RB_BLACK;
+                                rb_set_colour(other, rb_colour(parent));
+                                rb_set_black(parent);
                                 if (other->rb_right)
-                                        other->rb_right->rb_color = RB_BLACK;
+                                        rb_set_black(other->rb_right);
                                 __rb_rotate_left(parent, root);
                                 node = root->rb_node;
                                 break;
@@ -179,38 +182,35 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
                 else
                 {
                         other = parent->rb_left;
-                        if (other->rb_color == RB_RED)
+                        if (rb_is_red(other))
                         {
-                                other->rb_color = RB_BLACK;
-                                parent->rb_color = RB_RED;
+                                rb_set_black(other);
+                                rb_set_red(parent);
                                 __rb_rotate_right(parent, root);
                                 other = parent->rb_left;
                         }
-                        if ((!other->rb_left ||
-                             other->rb_left->rb_color == RB_BLACK)
-                            && (!other->rb_right ||
-                                other->rb_right->rb_color == RB_BLACK))
+                        if ((!other->rb_left || rb_is_black(other->rb_left)) &&
+                            (!other->rb_right || rb_is_black(other->rb_right)))
                         {
-                                other->rb_color = RB_RED;
+                                rb_set_red(other);
                                 node = parent;
-                                parent = node->rb_parent;
+                                parent = rb_parent(node);
                         }
                         else
                         {
-                                if (!other->rb_left ||
-                                    other->rb_left->rb_color == RB_BLACK)
+                                if (!other->rb_left || rb_is_black(other->rb_left))
                                 {
                                         register struct rb_node *o_right;
                                         if ((o_right = other->rb_right))
-                                                o_right->rb_color = RB_BLACK;
-                                        other->rb_color = RB_RED;
+                                                rb_set_black(o_right);
+                                        rb_set_red(other);
                                         __rb_rotate_left(other, root);
                                         other = parent->rb_left;
                                 }
-                                other->rb_color = parent->rb_color;
-                                parent->rb_color = RB_BLACK;
+                                rb_set_colour(other, rb_colour(parent));
+                                rb_set_black(parent);
                                 if (other->rb_left)
-                                        other->rb_left->rb_color = RB_BLACK;
+                                        rb_set_black(other->rb_left);
                                 __rb_rotate_right(parent, root);
                                 node = root->rb_node;
                                 break;
@@ -218,7 +218,7 @@ static void __rb_erase_color(struct rb_node *node, struct rb_node *parent,
                 }
         }
         if (node)
-                node->rb_color = RB_BLACK;
+                rb_set_black(node);
 }
 
 void rb_erase(struct rb_node *node, struct rb_root *root)
@@ -238,43 +238,41 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
                 while ((left = node->rb_left) != NULL)
                         node = left;
                 child = node->rb_right;
-                parent = node->rb_parent;
-                color = node->rb_color;
+                parent = rb_parent(node);
+                color = rb_colour(node);
 
                 if (child)
-                        child->rb_parent = parent;
-
-                if (node->rb_parent == old) {
+                        rb_set_parent(child, parent);
+                if (parent == old) {
                         parent->rb_right = child;
                         parent = node;
-                } else                  
+                } else
                         parent->rb_left = child;
 
-                node->rb_parent = old->rb_parent;
-                node->rb_color = old->rb_color;
+                node->rb_parent_colour = old->rb_parent_colour;
                 node->rb_right = old->rb_right;
                 node->rb_left = old->rb_left;
 
-                if (old->rb_parent)
+                if (rb_parent(old))
                 {
-                        if (old->rb_parent->rb_left == old)
-                                old->rb_parent->rb_left = node;
+                        if (rb_parent(old)->rb_left == old)
+                                rb_parent(old)->rb_left = node;
                         else
-                                old->rb_parent->rb_right = node;
+                                rb_parent(old)->rb_right = node;
                 } else
                         root->rb_node = node;
 
-                old->rb_left->rb_parent = node;
+                rb_set_parent(old->rb_left, node);
                 if (old->rb_right)
-                        old->rb_right->rb_parent = node;
+                        rb_set_parent(old->rb_right, node);
                 goto color;
         }
 
-        parent = node->rb_parent;
-        color = node->rb_color;
+        parent = rb_parent(node);
+        color = rb_colour(node);
 
         if (child)
-                child->rb_parent = parent;
+                rb_set_parent(child, parent);
         if (parent)
         {
                 if (parent->rb_left == node)
@@ -322,6 +320,8 @@ EXPORT_SYMBOL(rb_last);
 
 struct rb_node *rb_next(struct rb_node *node)
 {
+        struct rb_node *parent;
+
         /* If we have a right-hand child, go down and then left as far
            as we can. */
         if (node->rb_right) {
@@ -337,15 +337,17 @@ struct rb_node *rb_next(struct rb_node *node)
            ancestor is a right-hand child of its parent, keep going
            up. First time it's a left-hand child of its parent, said
            parent is our 'next' node. */
-        while (node->rb_parent && node == node->rb_parent->rb_right)
-                node = node->rb_parent;
+        while ((parent = rb_parent(node)) && node == parent->rb_right)
+                node = parent;
 
-        return node->rb_parent;
+        return parent;
 }
 EXPORT_SYMBOL(rb_next);
 
 struct rb_node *rb_prev(struct rb_node *node)
 {
+        struct rb_node *parent;
+
         /* If we have a left-hand child, go down and then right as far
            as we can. */
         if (node->rb_left) {
@@ -357,17 +359,17 @@ struct rb_node *rb_prev(struct rb_node *node)
 
         /* No left-hand children. Go up till we find an ancestor which
            is a right-hand child of its parent */
-        while (node->rb_parent && node == node->rb_parent->rb_left)
-                node = node->rb_parent;
+        while ((parent = rb_parent(node)) && node == parent->rb_left)
+                node = parent;
 
-        return node->rb_parent;
+        return parent;
 }
 EXPORT_SYMBOL(rb_prev);
 
 void rb_replace_node(struct rb_node *victim, struct rb_node *new,
                      struct rb_root *root)
 {
-        struct rb_node *parent = victim->rb_parent;
+        struct rb_node *parent = rb_parent(victim);
 
         /* Set the surrounding nodes to point to the replacement */
         if (parent) {
@@ -379,9 +381,9 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new,
                 root->rb_node = new;
         }
         if (victim->rb_left)
-                victim->rb_left->rb_parent = new;
+                rb_set_parent(victim->rb_left, new);
         if (victim->rb_right)
-                victim->rb_right->rb_parent = new;
+                rb_set_parent(victim->rb_right, new);
 
         /* Copy the pointers/colour from the victim to the replacement */
         *new = *victim;