radix-tree: remove root->height

The only remaining references to root->height were in extend and shrink,
where it was updated.  Now we can remove it entirely.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 75 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 75c9e6197b5b..58f79fee8c71 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -39,12 +39,6 @@
 
 
 /*
- * The height_to_maxindex array needs to be one deeper than the maximum
- * path as height 0 holds only 1 entry.
- */
-static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH + 1] __read_mostly;
-
-/*
  * Radix tree node cache.
  */
 static struct kmem_cache *radix_tree_node_cachep;
@@ -218,8 +212,7 @@ radix_tree_find_next_bit(const unsigned long *addr,
 }
 
 #ifndef __KERNEL__
-static void dump_node(struct radix_tree_node *node,
-                                unsigned shift, unsigned long index)
+static void dump_node(struct radix_tree_node *node, unsigned long index)
 {
         unsigned long i;
 
@@ -229,8 +222,8 @@ static void dump_node(struct radix_tree_node *node,
                 node->shift, node->count, node->parent);
 
         for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
-                unsigned long first = index | (i << shift);
-                unsigned long last = first | ((1UL << shift) - 1);
+                unsigned long first = index | (i << node->shift);
+                unsigned long last = first | ((1UL << node->shift) - 1);
                 void *entry = node->slots[i];
                 if (!entry)
                         continue;
@@ -243,8 +236,7 @@ static void dump_node(struct radix_tree_node *node,
                         pr_debug("radix entry %p offset %ld indices %ld-%ld\n",
                                         entry, i, first, last);
                 } else {
-                        dump_node(indirect_to_ptr(entry),
-                                        shift - RADIX_TREE_MAP_SHIFT, first);
+                        dump_node(indirect_to_ptr(entry), first);
                 }
         }
 }
@@ -252,13 +244,12 @@ static void dump_node(struct radix_tree_node *node,
 /* For debug */
 static void radix_tree_dump(struct radix_tree_root *root)
 {
-        pr_debug("radix root: %p height %d rnode %p tags %x\n",
-                        root, root->height, root->rnode,
+        pr_debug("radix root: %p rnode %p tags %x\n",
+                        root, root->rnode,
                         root->gfp_mask >> __GFP_BITS_SHIFT);
         if (!radix_tree_is_indirect_ptr(root->rnode))
                 return;
-        dump_node(indirect_to_ptr(root->rnode),
-                                (root->height - 1) * RADIX_TREE_MAP_SHIFT, 0);
+        dump_node(indirect_to_ptr(root->rnode), 0);
 }
 #endif
 
@@ -411,14 +402,8 @@ int radix_tree_maybe_preload(gfp_t gfp_mask)
 EXPORT_SYMBOL(radix_tree_maybe_preload);
 
 /*
- *      Return the maximum key which can be store into a
- *      radix tree with height HEIGHT.
+ * The maximum index which can be stored in a radix tree
  */
-static inline unsigned long radix_tree_maxindex(unsigned int height)
-{
-        return height_to_maxindex[height];
-}
-
 static inline unsigned long shift_maxindex(unsigned int shift)
 {
         return (RADIX_TREE_MAP_SIZE << shift) - 1;
@@ -450,24 +435,22 @@ static unsigned radix_tree_load_root(struct radix_tree_root *root,
  *      Extend a radix tree so it can store key @index.
  */
 static int radix_tree_extend(struct radix_tree_root *root,
-                                unsigned long index)
+                                unsigned long index, unsigned int shift)
 {
         struct radix_tree_node *slot;
-        unsigned int height;
+        unsigned int maxshift;
         int tag;
 
-        /* Figure out what the height should be.  */
-        height = root->height + 1;
-        while (index > radix_tree_maxindex(height))
-                height++;
+        /* Figure out what the shift should be.  */
+        maxshift = shift;
+        while (index > shift_maxindex(maxshift))
+                maxshift += RADIX_TREE_MAP_SHIFT;
 
-        if (root->rnode == NULL) {
-                root->height = height;
+        slot = root->rnode;
+        if (!slot)
                 goto out;
-        }
 
         do {
-                unsigned int newheight;
                 struct radix_tree_node *node = radix_tree_node_alloc(root);
 
                 if (!node)
@@ -479,14 +462,11 @@ static int radix_tree_extend(struct radix_tree_root *root,
                                 tag_set(node, tag, 0);
                 }
 
-                /* Increase the height.  */
-                newheight = root->height;
-                BUG_ON(newheight > BITS_PER_LONG);
-                node->shift = newheight * RADIX_TREE_MAP_SHIFT;
+                BUG_ON(shift > BITS_PER_LONG);
+                node->shift = shift;
                 node->offset = 0;
                 node->count = 1;
                 node->parent = NULL;
-                slot = root->rnode;
                 if (radix_tree_is_indirect_ptr(slot)) {
                         slot = indirect_to_ptr(slot);
                         slot->parent = node;
@@ -495,10 +475,11 @@ static int radix_tree_extend(struct radix_tree_root *root,
                 node->slots[0] = slot;
                 node = ptr_to_indirect(node);
                 rcu_assign_pointer(root->rnode, node);
-                root->height = ++newheight;
-        } while (height > root->height);
+                shift += RADIX_TREE_MAP_SHIFT;
+                slot = node;
+        } while (shift <= maxshift);
 out:
-        return height * RADIX_TREE_MAP_SHIFT;
+        return maxshift + RADIX_TREE_MAP_SHIFT;
 }
 
 /**
@@ -531,15 +512,13 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 
         /* Make sure the tree is high enough.  */
         if (max > maxindex) {
-                int error = radix_tree_extend(root, max);
+                int error = radix_tree_extend(root, max, shift);
                 if (error < 0)
                         return error;
                 shift = error;
                 slot = root->rnode;
-                if (order == shift) {
+                if (order == shift)
                         shift += RADIX_TREE_MAP_SHIFT;
-                        root->height++;
-                }
         }
 
         offset = 0;                     /* uninitialised var warning */
@@ -1412,32 +1391,32 @@ unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
 #endif /* CONFIG_SHMEM && CONFIG_SWAP */
 
 /**
- *      radix_tree_shrink    -    shrink height of a radix tree to minimal
+ *      radix_tree_shrink    -    shrink radix tree to minimum height
  *      @root           radix tree root
  */
 static inline bool radix_tree_shrink(struct radix_tree_root *root)
 {
         bool shrunk = false;
 
-        /* try to shrink tree height */
-        while (root->height > 0) {
+        for (;;) {
                 struct radix_tree_node *to_free = root->rnode;
                 struct radix_tree_node *slot;
 
-                BUG_ON(!radix_tree_is_indirect_ptr(to_free));
+                if (!radix_tree_is_indirect_ptr(to_free))
+                        break;
                 to_free = indirect_to_ptr(to_free);
 
                 /*
                  * The candidate node has more than one child, or its child
-                 * is not at the leftmost slot, or it is a multiorder entry,
-                 * we cannot shrink.
+                 * is not at the leftmost slot, or the child is a multiorder
+                 * entry, we cannot shrink.
                  */
                 if (to_free->count != 1)
                         break;
                 slot = to_free->slots[0];
                 if (!slot)
                         break;
-                if (!radix_tree_is_indirect_ptr(slot) && (root->height > 1))
+                if (!radix_tree_is_indirect_ptr(slot) && to_free->shift)
                         break;
 
                 if (radix_tree_is_indirect_ptr(slot)) {
@@ -1454,7 +1433,6 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root)
                  * one (root->rnode) as far as dependent read barriers go.
                  */
                 root->rnode = slot;
-                root->height--;
 
                 /*
                  * We have a dilemma here. The node's slot[0] must not be
@@ -1515,7 +1493,6 @@ bool __radix_tree_delete_node(struct radix_tree_root *root,
                         parent->count--;
                 } else {
                         root_tag_clear_all(root);
-                        root->height = 0;
                         root->rnode = NULL;
                 }
 
@@ -1631,26 +1608,6 @@ radix_tree_node_ctor(void *arg)
         INIT_LIST_HEAD(&node->private_list);
 }
 
-static __init unsigned long __maxindex(unsigned int height)
-{
-        unsigned int width = height * RADIX_TREE_MAP_SHIFT;
-        int shift = RADIX_TREE_INDEX_BITS - width;
-
-        if (shift < 0)
-                return ~0UL;
-        if (shift >= BITS_PER_LONG)
-                return 0UL;
-        return ~0UL >> shift;
-}
-
-static __init void radix_tree_init_maxindex(void)
-{
-        unsigned int i;
-
-        for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
-                height_to_maxindex[i] = __maxindex(i);
-}
-
 static int radix_tree_callback(struct notifier_block *nfb,
                                 unsigned long action, void *hcpu)
 {
@@ -1677,6 +1634,5 @@ void __init radix_tree_init(void)
                         sizeof(struct radix_tree_node), 0,
                         SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
                         radix_tree_node_ctor);
-        radix_tree_init_maxindex();
         hotcpu_notifier(radix_tree_callback, 0);
 }