lib: radix_tree: tree node interface

Make struct radix_tree_node part of the public interface and provide API
functions to create, look up, and delete whole nodes.  Refactor the
existing insert, look up, delete functions on top of these new node
primitives.

This will allow the VM to track and garbage collect page cache radix
tree nodes.

[sasha.levin@oracle.com: return correct error code on insertion failure]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bob Liu <bob.liu@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Luigi Semenzato <semenzato@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Metin Doslu <metin@citusdata.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ozgun Erdogan <ozgun@citusdata.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin <klamm@yandex-team.ru>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/radix-tree.h

@@ -60,6 +60,33 @@ static inline int radix_tree_is_indirect_ptr(void *ptr)
 
 #define RADIX_TREE_MAX_TAGS 3
 
+#ifdef __KERNEL__
+#define RADIX_TREE_MAP_SHIFT	(CONFIG_BASE_SMALL ? 4 : 6)
+#else
+#define RADIX_TREE_MAP_SHIFT	3	/* For more stressful testing */
+#endif
+
+#define RADIX_TREE_MAP_SIZE	(1UL << RADIX_TREE_MAP_SHIFT)
+#define RADIX_TREE_MAP_MASK	(RADIX_TREE_MAP_SIZE-1)
+
+#define RADIX_TREE_TAG_LONGS	\
+	((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
+
+struct radix_tree_node {
+	unsigned int	height;		/* Height from the bottom */
+	unsigned int	count;
+	union {
+		struct radix_tree_node *parent;	/* Used when ascending tree */
+		struct rcu_head	rcu_head;	/* Used when freeing node */
+	};
+	void __rcu	*slots[RADIX_TREE_MAP_SIZE];
+	unsigned long	tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
+};
+
+#define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
+#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
+					  RADIX_TREE_MAP_SHIFT))
+
 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
 struct radix_tree_root {
 	unsigned int		height;
@@ -101,6 +128,7 @@ do {									\
  *   concurrently with other readers.
  *
  * The notable exceptions to this rule are the following functions:
+ * __radix_tree_lookup
  * radix_tree_lookup
  * radix_tree_lookup_slot
  * radix_tree_tag_get
@@ -216,9 +244,15 @@ static inline void radix_tree_replace_slot(void **pslot, void *item)
 	rcu_assign_pointer(*pslot, item);
 }
 
+int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
+			struct radix_tree_node **nodep, void ***slotp);
 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
+void *__radix_tree_lookup(struct radix_tree_root *root, unsigned long index,
+			  struct radix_tree_node **nodep, void ***slotp);
 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
+bool __radix_tree_delete_node(struct radix_tree_root *root, unsigned long index,
+			      struct radix_tree_node *node);
 void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 unsigned int