radix-tree: replace node->height with node->shift

node->shift represents the shift necessary for looking in the slots
array at this level.  It is equal to the old (node->height - 1) *
RADIX_TREE_MAP_SHIFT.

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>
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 2d2ad9d6..0374582 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -89,7 +89,7 @@
 #define RADIX_TREE_COUNT_MASK	((1UL << RADIX_TREE_COUNT_SHIFT) - 1)
 
 struct radix_tree_node {
-	unsigned char	height;	/* From the bottom */
+	unsigned char	shift;	/* Bits remaining in each slot */
 	unsigned char	offset;	/* Slot offset in parent */
 	unsigned int	count;
 	union {