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>

lib/Kconfig

@@ -362,6 +362,9 @@ config INTERVAL_TREE
 
 	  for more information.
 
+config RADIX_TREE_MULTIORDER
+	bool
+
 config ASSOCIATIVE_ARRAY
 	bool
 	help

lib/radix-tree.c

@@ -484,6 +484,7 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 		slot = node->slots[offset];
 	}
 
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
 	/* Insert pointers to the canonical entry */
 	if ((shift - order) > 0) {
 		int i, n = 1 << (shift - order);
@@ -499,6 +500,7 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 			node->count++;
 		}
 	}
+#endif
 
 	if (nodep)
 		*nodep = node;
@@ -1469,6 +1471,20 @@ bool __radix_tree_delete_node(struct radix_tree_root *root,
 	return deleted;
 }
 
+static inline void delete_sibling_entries(struct radix_tree_node *node,
+					void *ptr, unsigned offset)
+{
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+	int i;
+	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
+		if (node->slots[offset + i] != ptr)
+			break;
+		node->slots[offset + i] = NULL;
+		node->count--;
+	}
+#endif
+}
+
 /**
  *	radix_tree_delete_item    -    delete an item from a radix tree
  *	@root:		radix tree root
@@ -1484,7 +1500,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
 			     unsigned long index, void *item)
 {
 	struct radix_tree_node *node;
-	unsigned int offset, i;
+	unsigned int offset;
 	void **slot;
 	void *entry;
 	int tag;
@@ -1513,13 +1529,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
 			radix_tree_tag_clear(root, index, tag);
 	}
 
-	/* Delete any sibling slots pointing to this slot */
-	for (i = 1; offset + i < RADIX_TREE_MAP_SIZE; i++) {
-		if (node->slots[offset + i] != ptr_to_indirect(slot))
-			break;
-		node->slots[offset + i] = NULL;
-		node->count--;
-	}
+	delete_sibling_entries(node, ptr_to_indirect(slot), offset);
 	node->slots[offset] = NULL;
 	node->count--;
 

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.

tools/testing/radix-tree/linux/kernel.h

@@ -9,6 +9,7 @@
 
 #include "../../include/linux/compiler.h"
 
+#define CONFIG_RADIX_TREE_MULTIORDER
 #define CONFIG_SHMEM
 #define CONFIG_SWAP