generic radix trees

Very simple radix tree implementation that supports storing arbitrary
size entries, up to PAGE_SIZE - upcoming patches will convert existing
flex_array users to genradixes.  The new genradix code has a much
simpler API and implementation, and doesn't have a hard limit on the
number of elements like flex_array does.

Link: http://lkml.kernel.org/r/20181217131929.11727-5-kent.overstreet@gmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Pravin B Shelar <pshelar@ovn.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 231 insertions, 0 deletions

diff --git a/include/linux/generic-radix-tree.h b/include/linux/generic-radix-tree.h
new file mode 100644
index 000000000000..3a91130a4fbd
--- /dev/null
+++ b/include/linux/generic-radix-tree.h
@@ -0,0 +1,231 @@
+#ifndef _LINUX_GENERIC_RADIX_TREE_H
+#define _LINUX_GENERIC_RADIX_TREE_H
+
+/**
+ * DOC: Generic radix trees/sparse arrays:
+ *
+ * Very simple and minimalistic, supporting arbitrary size entries up to
+ * PAGE_SIZE.
+ *
+ * A genradix is defined with the type it will store, like so:
+ *
+ * static GENRADIX(struct foo) foo_genradix;
+ *
+ * The main operations are:
+ *
+ * - genradix_init(radix) - initialize an empty genradix
+ *
+ * - genradix_free(radix) - free all memory owned by the genradix and
+ *   reinitialize it
+ *
+ * - genradix_ptr(radix, idx) - gets a pointer to the entry at idx, returning
+ *   NULL if that entry does not exist
+ *
+ * - genradix_ptr_alloc(radix, idx, gfp) - gets a pointer to an entry,
+ *   allocating it if necessary
+ *
+ * - genradix_for_each(radix, iter, p) - iterate over each entry in a genradix
+ *
+ * The radix tree allocates one page of entries at a time, so entries may exist
+ * that were never explicitly allocated - they will be initialized to all
+ * zeroes.
+ *
+ * Internally, a genradix is just a radix tree of pages, and indexing works in
+ * terms of byte offsets. The wrappers in this header file use sizeof on the
+ * type the radix contains to calculate a byte offset from the index - see
+ * __idx_to_offset.
+ */
+
+#include <asm/page.h>
+#include <linux/bug.h>
+#include <linux/kernel.h>
+#include <linux/log2.h>
+
+struct genradix_root;
+
+struct __genradix {
+	struct genradix_root __rcu	*root;
+};
+
+/*
+ * NOTE: currently, sizeof(_type) must not be larger than PAGE_SIZE:
+ */
+
+#define __GENRADIX_INITIALIZER					\
+	{							\
+		.tree = {					\
+			.root = NULL,				\
+		}						\
+	}
+
+/*
+ * We use a 0 size array to stash the type we're storing without taking any
+ * space at runtime - then the various accessor macros can use typeof() to get
+ * to it for casts/sizeof - we also force the alignment so that storing a type
+ * with a ridiculous alignment doesn't blow up the alignment or size of the
+ * genradix.
+ */
+
+#define GENRADIX(_type)						\
+struct {							\
+	struct __genradix	tree;				\
+	_type			type[0] __aligned(1);		\
+}
+
+#define DEFINE_GENRADIX(_name, _type)				\
+	GENRADIX(_type) _name = __GENRADIX_INITIALIZER
+
+/**
+ * genradix_init - initialize a genradix
+ * @_radix:	genradix to initialize
+ *
+ * Does not fail
+ */
+#define genradix_init(_radix)					\
+do {								\
+	*(_radix) = (typeof(*_radix)) __GENRADIX_INITIALIZER;	\
+} while (0)
+
+void __genradix_free(struct __genradix *);
+
+/**
+ * genradix_free: free all memory owned by a genradix
+ * @_radix: the genradix to free
+ *
+ * After freeing, @_radix will be reinitialized and empty
+ */
+#define genradix_free(_radix)	__genradix_free(&(_radix)->tree)
+
+static inline size_t __idx_to_offset(size_t idx, size_t obj_size)
+{
+	if (__builtin_constant_p(obj_size))
+		BUILD_BUG_ON(obj_size > PAGE_SIZE);
+	else
+		BUG_ON(obj_size > PAGE_SIZE);
+
+	if (!is_power_of_2(obj_size)) {
+		size_t objs_per_page = PAGE_SIZE / obj_size;
+
+		return (idx / objs_per_page) * PAGE_SIZE +
+			(idx % objs_per_page) * obj_size;
+	} else {
+		return idx * obj_size;
+	}
+}
+
+#define __genradix_cast(_radix)		(typeof((_radix)->type[0]) *)
+#define __genradix_obj_size(_radix)	sizeof((_radix)->type[0])
+#define __genradix_idx_to_offset(_radix, _idx)			\
+	__idx_to_offset(_idx, __genradix_obj_size(_radix))
+
+void *__genradix_ptr(struct __genradix *, size_t);
+
+/**
+ * genradix_ptr - get a pointer to a genradix entry
+ * @_radix:	genradix to access
+ * @_idx:	index to fetch
+ *
+ * Returns a pointer to entry at @_idx, or NULL if that entry does not exist.
+ */
+#define genradix_ptr(_radix, _idx)				\
+	(__genradix_cast(_radix)				\
+	 __genradix_ptr(&(_radix)->tree,			\
+			__genradix_idx_to_offset(_radix, _idx)))
+
+void *__genradix_ptr_alloc(struct __genradix *, size_t, gfp_t);
+
+/**
+ * genradix_ptr_alloc - get a pointer to a genradix entry, allocating it
+ *			if necessary
+ * @_radix:	genradix to access
+ * @_idx:	index to fetch
+ * @_gfp:	gfp mask
+ *
+ * Returns a pointer to entry at @_idx, or NULL on allocation failure
+ */
+#define genradix_ptr_alloc(_radix, _idx, _gfp)			\
+	(__genradix_cast(_radix)				\
+	 __genradix_ptr_alloc(&(_radix)->tree,			\
+			__genradix_idx_to_offset(_radix, _idx),	\
+			_gfp))
+
+struct genradix_iter {
+	size_t			offset;
+	size_t			pos;
+};
+
+/**
+ * genradix_iter_init - initialize a genradix_iter
+ * @_radix:	genradix that will be iterated over
+ * @_idx:	index to start iterating from
+ */
+#define genradix_iter_init(_radix, _idx)			\
+	((struct genradix_iter) {				\
+		.pos	= (_idx),				\
+		.offset	= __genradix_idx_to_offset((_radix), (_idx)),\
+	})
+
+void *__genradix_iter_peek(struct genradix_iter *, struct __genradix *, size_t);
+
+/**
+ * genradix_iter_peek - get first entry at or above iterator's current
+ *			position
+ * @_iter:	a genradix_iter
+ * @_radix:	genradix being iterated over
+ *
+ * If no more entries exist at or above @_iter's current position, returns NULL
+ */
+#define genradix_iter_peek(_iter, _radix)			\
+	(__genradix_cast(_radix)				\
+	 __genradix_iter_peek(_iter, &(_radix)->tree,		\
+			      PAGE_SIZE / __genradix_obj_size(_radix)))
+
+static inline void __genradix_iter_advance(struct genradix_iter *iter,
+					   size_t obj_size)
+{
+	iter->offset += obj_size;
+
+	if (!is_power_of_2(obj_size) &&
+	    (iter->offset & (PAGE_SIZE - 1)) + obj_size > PAGE_SIZE)
+		iter->offset = round_up(iter->offset, PAGE_SIZE);
+
+	iter->pos++;
+}
+
+#define genradix_iter_advance(_iter, _radix)			\
+	__genradix_iter_advance(_iter, __genradix_obj_size(_radix))
+
+#define genradix_for_each_from(_radix, _iter, _p, _start)	\
+	for (_iter = genradix_iter_init(_radix, _start);	\
+	     (_p = genradix_iter_peek(&_iter, _radix)) != NULL;	\
+	     genradix_iter_advance(&_iter, _radix))
+
+/**
+ * genradix_for_each - iterate over entry in a genradix
+ * @_radix:	genradix to iterate over
+ * @_iter:	a genradix_iter to track current position
+ * @_p:		pointer to genradix entry type
+ *
+ * On every iteration, @_p will point to the current entry, and @_iter.pos
+ * will be the current entry's index.
+ */
+#define genradix_for_each(_radix, _iter, _p)			\
+	genradix_for_each_from(_radix, _iter, _p, 0)
+
+int __genradix_prealloc(struct __genradix *, size_t, gfp_t);
+
+/**
+ * genradix_prealloc - preallocate entries in a generic radix tree
+ * @_radix:	genradix to preallocate
+ * @_nr:	number of entries to preallocate
+ * @_gfp:	gfp mask
+ *
+ * Returns 0 on success, -ENOMEM on failure
+ */
+#define genradix_prealloc(_radix, _nr, _gfp)			\
+	 __genradix_prealloc(&(_radix)->tree,			\
+			__genradix_idx_to_offset(_radix, _nr + 1),\
+			_gfp)
+
+
+#endif /* _LINUX_GENERIC_RADIX_TREE_H */