[PATCH] Use table lookup for radix_tree_maxindex()

Patch from Szabolcs Berecz <szabi@mplayerhq.hu>

With the following patch maxindex is taken from an array instead of
recalculating it all the time.

lib/radix-tree.c

@@ -46,6 +46,8 @@ struct radix_tree_path {
 #define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
 #define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
 
+static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH];
+
 /*
  * Radix tree node cache.
  */
@@ -126,12 +128,7 @@ int radix_tree_preload(int gfp_mask)
  */
 static inline unsigned long radix_tree_maxindex(unsigned int height)
 {
-	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
-	unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
-
-	if (tmp >= RADIX_TREE_INDEX_BITS)
-		index = ~0UL;
-	return index;
+	return height_to_maxindex[height];
 }
 
 /*
@@ -401,6 +398,24 @@ radix_tree_node_ctor(void *node, kmem_cache_t *cachep, unsigned long flags)
 	memset(node, 0, sizeof(struct radix_tree_node));
 }
 
+static __init unsigned long __maxindex(unsigned int height)
+{
+	unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
+	unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
+
+	if (tmp >= RADIX_TREE_INDEX_BITS)
+		index = ~0UL;
+	return index;
+}
+
+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);
+}
+
 void __init radix_tree_init(void)
 {
 	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
@@ -408,4 +423,5 @@ void __init radix_tree_init(void)
 			0, radix_tree_node_ctor, NULL);
 	if (!radix_tree_node_cachep)
 		panic ("Failed to create radix_tree_node cache\n");
+	radix_tree_init_maxindex();
 }