raxix-tree: introduce CONFIG_RADIX_TREE_MULTIORDER

I've been receiving increasingly concerned notes from 0day about how
much my recent changes have been bloating the radix tree.  Make it
happier by only including multiorder support if
CONFIG_TRANSPARENT_HUGEPAGES is set.

This is an independent Kconfig option, so other radix tree users can
also set it if they have a need.

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>

mm/Kconfig

@@ -404,6 +404,7 @@ config TRANSPARENT_HUGEPAGE
 	bool "Transparent Hugepage Support"
 	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select COMPACTION
+	select RADIX_TREE_MULTIORDER
 	help
 	  Transparent Hugepages allows the kernel to use huge pages and
 	  huge tlb transparently to the applications whenever possible.