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Message-Id: <20181217131929.11727-5-kent.overstreet@gmail.com>
Date: Mon, 17 Dec 2018 08:19:26 -0500
From: Kent Overstreet <kent.overstreet@...il.com>
To: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...il.com>
Subject: [PATCH 4/7] 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.
Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
---
Documentation/core-api/generic-radix-tree.rst | 12 +
Documentation/core-api/index.rst | 1 +
include/linux/generic-radix-tree.h | 231 ++++++++++++++++++
lib/Makefile | 3 +-
lib/generic-radix-tree.c | 217 ++++++++++++++++
5 files changed, 463 insertions(+), 1 deletion(-)
create mode 100644 Documentation/core-api/generic-radix-tree.rst
create mode 100644 include/linux/generic-radix-tree.h
create mode 100644 lib/generic-radix-tree.c
diff --git a/Documentation/core-api/generic-radix-tree.rst b/Documentation/core-api/generic-radix-tree.rst
new file mode 100644
index 0000000000..80fd27440f
--- /dev/null
+++ b/Documentation/core-api/generic-radix-tree.rst
@@ -0,0 +1,12 @@
+=================================
+Generic radix trees/sparse arrays
+=================================
+
+.. kernel-doc:: include/linux/generic-radix-tree.h
+ :doc: Generic radix trees/sparse arrays
+
+generic radix tree functions
+----------------------------
+
+.. kernel-doc:: include/linux/generic-radix-tree.h
+ :functions:
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index 3adee82be3..6870baffef 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -28,6 +28,7 @@ Core utilities
errseq
printk-formats
circular-buffers
+ generic-radix-tree
memory-allocation
mm-api
gfp_mask-from-fs-io
diff --git a/include/linux/generic-radix-tree.h b/include/linux/generic-radix-tree.h
new file mode 100644
index 0000000000..3a91130a4f
--- /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 */
diff --git a/lib/Makefile b/lib/Makefile
index db06d12378..f48beff23b 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -38,7 +38,8 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \
gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
bsearch.o find_bit.o llist.o memweight.o kfifo.o \
percpu-refcount.o rhashtable.o reciprocal_div.o \
- once.o refcount.o usercopy.o errseq.o bucket_locks.o
+ once.o refcount.o usercopy.o errseq.o bucket_locks.o \
+ generic-radix-tree.o
obj-$(CONFIG_STRING_SELFTEST) += test_string.o
obj-y += string_helpers.o
obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
diff --git a/lib/generic-radix-tree.c b/lib/generic-radix-tree.c
new file mode 100644
index 0000000000..a7bafc4137
--- /dev/null
+++ b/lib/generic-radix-tree.c
@@ -0,0 +1,217 @@
+
+#include <linux/export.h>
+#include <linux/generic-radix-tree.h>
+#include <linux/gfp.h>
+
+#define GENRADIX_ARY (PAGE_SIZE / sizeof(struct genradix_node *))
+#define GENRADIX_ARY_SHIFT ilog2(GENRADIX_ARY)
+
+struct genradix_node {
+ union {
+ /* Interior node: */
+ struct genradix_node *children[GENRADIX_ARY];
+
+ /* Leaf: */
+ u8 data[PAGE_SIZE];
+ };
+};
+
+static inline int genradix_depth_shift(unsigned depth)
+{
+ return PAGE_SHIFT + GENRADIX_ARY_SHIFT * depth;
+}
+
+/*
+ * Returns size (of data, in bytes) that a tree of a given depth holds:
+ */
+static inline size_t genradix_depth_size(unsigned depth)
+{
+ return 1UL << genradix_depth_shift(depth);
+}
+
+/* depth that's needed for a genradix that can address up to ULONG_MAX: */
+#define GENRADIX_MAX_DEPTH \
+ DIV_ROUND_UP(BITS_PER_LONG - PAGE_SHIFT, GENRADIX_ARY_SHIFT)
+
+#define GENRADIX_DEPTH_MASK \
+ ((unsigned long) (roundup_pow_of_two(GENRADIX_MAX_DEPTH + 1) - 1))
+
+unsigned genradix_root_to_depth(struct genradix_root *r)
+{
+ return (unsigned long) r & GENRADIX_DEPTH_MASK;
+}
+
+struct genradix_node *genradix_root_to_node(struct genradix_root *r)
+{
+ return (void *) ((unsigned long) r & ~GENRADIX_DEPTH_MASK);
+}
+
+/*
+ * Returns pointer to the specified byte @offset within @radix, or NULL if not
+ * allocated
+ */
+void *__genradix_ptr(struct __genradix *radix, size_t offset)
+{
+ struct genradix_root *r = READ_ONCE(radix->root);
+ struct genradix_node *n = genradix_root_to_node(r);
+ unsigned level = genradix_root_to_depth(r);
+
+ if (ilog2(offset) >= genradix_depth_shift(level))
+ return NULL;
+
+ while (1) {
+ if (!n)
+ return NULL;
+ if (!level)
+ break;
+
+ level--;
+
+ n = n->children[offset >> genradix_depth_shift(level)];
+ offset &= genradix_depth_size(level) - 1;
+ }
+
+ return &n->data[offset];
+}
+EXPORT_SYMBOL(__genradix_ptr);
+
+/*
+ * Returns pointer to the specified byte @offset within @radix, allocating it if
+ * necessary - newly allocated slots are always zeroed out:
+ */
+void *__genradix_ptr_alloc(struct __genradix *radix, size_t offset,
+ gfp_t gfp_mask)
+{
+ struct genradix_root *v = READ_ONCE(radix->root);
+ struct genradix_node *n, *new_node = NULL;
+ unsigned level;
+
+ /* Increase tree depth if necessary: */
+ while (1) {
+ struct genradix_root *r = v, *new_root;
+
+ n = genradix_root_to_node(r);
+ level = genradix_root_to_depth(r);
+
+ if (n && ilog2(offset) < genradix_depth_shift(level))
+ break;
+
+ if (!new_node) {
+ new_node = (void *)
+ __get_free_page(gfp_mask|__GFP_ZERO);
+ if (!new_node)
+ return NULL;
+ }
+
+ new_node->children[0] = n;
+ new_root = ((struct genradix_root *)
+ ((unsigned long) new_node | (n ? level + 1 : 0)));
+
+ if ((v = cmpxchg_release(&radix->root, r, new_root)) == r) {
+ v = new_root;
+ new_node = NULL;
+ }
+ }
+
+ while (level--) {
+ struct genradix_node **p =
+ &n->children[offset >> genradix_depth_shift(level)];
+ offset &= genradix_depth_size(level) - 1;
+
+ n = READ_ONCE(*p);
+ if (!n) {
+ if (!new_node) {
+ new_node = (void *)
+ __get_free_page(gfp_mask|__GFP_ZERO);
+ if (!new_node)
+ return NULL;
+ }
+
+ if (!(n = cmpxchg_release(p, NULL, new_node)))
+ swap(n, new_node);
+ }
+ }
+
+ if (new_node)
+ free_page((unsigned long) new_node);
+
+ return &n->data[offset];
+}
+EXPORT_SYMBOL(__genradix_ptr_alloc);
+
+void *__genradix_iter_peek(struct genradix_iter *iter,
+ struct __genradix *radix,
+ size_t objs_per_page)
+{
+ struct genradix_root *r;
+ struct genradix_node *n;
+ unsigned level, i;
+restart:
+ r = READ_ONCE(radix->root);
+ if (!r)
+ return NULL;
+
+ n = genradix_root_to_node(r);
+ level = genradix_root_to_depth(r);
+
+ if (ilog2(iter->offset) >= genradix_depth_shift(level))
+ return NULL;
+
+ while (level) {
+ level--;
+
+ i = (iter->offset >> genradix_depth_shift(level)) &
+ (GENRADIX_ARY - 1);
+
+ while (!n->children[i]) {
+ i++;
+ iter->offset = round_down(iter->offset +
+ genradix_depth_size(level),
+ genradix_depth_size(level));
+ iter->pos = (iter->offset >> PAGE_SHIFT) *
+ objs_per_page;
+ if (i == GENRADIX_ARY)
+ goto restart;
+ }
+
+ n = n->children[i];
+ }
+
+ return &n->data[iter->offset & (PAGE_SIZE - 1)];
+}
+EXPORT_SYMBOL(__genradix_iter_peek);
+
+static void genradix_free_recurse(struct genradix_node *n, unsigned level)
+{
+ if (level) {
+ unsigned i;
+
+ for (i = 0; i < GENRADIX_ARY; i++)
+ if (n->children[i])
+ genradix_free_recurse(n->children[i], level - 1);
+ }
+
+ free_page((unsigned long) n);
+}
+
+int __genradix_prealloc(struct __genradix *radix, size_t size,
+ gfp_t gfp_mask)
+{
+ size_t offset;
+
+ for (offset = 0; offset < size; offset += PAGE_SIZE)
+ if (!__genradix_ptr_alloc(radix, offset, gfp_mask))
+ return -ENOMEM;
+
+ return 0;
+}
+EXPORT_SYMBOL(__genradix_prealloc);
+
+void __genradix_free(struct __genradix *radix)
+{
+ struct genradix_root *r = xchg(&radix->root, NULL);
+
+ genradix_free_recurse(genradix_root_to_node(r),
+ genradix_root_to_depth(r));
+}
+EXPORT_SYMBOL(__genradix_free);
--
2.20.1
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