[PATCH 27/32] lib/generic-radix-tree.c: Add peek_prev()

Kent Overstreet
2023-05-09T17:01:00Z

From: Kent Overstreet <kent.overstreet@gmail.com>

This patch adds genradix_peek_prev(), genradix_iter_rewind(), and
genradix_for_each_reverse(), for iterating backwards over a generic
radix tree.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
include/linux/generic-radix-tree.h | 61 +++++++++++++++++++++++++++++-
lib/generic-radix-tree.c | 59 +++++++++++++++++++++++++++++
2 files changed, 119 insertions(+), 1 deletion(-)

diff --git a/include/linux/generic-radix-tree.h b/include/linux/generic-radix-tree.h
index f6cd0f909d..c74b737699 100644
--- a/include/linux/generic-radix-tree.h
+++ b/include/linux/generic-radix-tree.h
@@ -117,6 +117,11 @@ static inline size_t __idx_to_offset(size_t idx, size_t obj_size)

#define __genradix_cast(_radix) (typeof((_radix)->type[0]) *)
#define __genradix_obj_size(_radix) sizeof((_radix)->type[0])
+#define __genradix_objs_per_page(_radix) \
+ (PAGE_SIZE / sizeof((_radix)->type[0]))
+#define __genradix_page_remainder(_radix) \
+ (PAGE_SIZE % sizeof((_radix)->type[0]))
+
#define __genradix_idx_to_offset(_radix, _idx) \
__idx_to_offset(_idx, __genradix_obj_size(_radix))

@@ -180,7 +185,25 @@ void *__genradix_iter_peek(struct genradix_iter *, struct __genradix *, size_t);
#define genradix_iter_peek(_iter, _radix) \
(__genradix_cast(_radix) \
__genradix_iter_peek(_iter, &(_radix)->tree, \
- PAGE_SIZE / __genradix_obj_size(_radix)))
+ __genradix_objs_per_page(_radix)))
+
+void *__genradix_iter_peek_prev(struct genradix_iter *, struct __genradix *,
+ size_t, size_t);
+
+/**
+ * genradix_iter_peek - get first entry at or below iterator's current
+ * position
+ * @_iter: a genradix_iter
+ * @_radix: genradix being iterated over
+ *
+ * If no more entries exist at or below @_iter's current position, returns NULL
+ */
+#define genradix_iter_peek_prev(_iter, _radix) \
+ (__genradix_cast(_radix) \
+ __genradix_iter_peek_prev(_iter, &(_radix)->tree, \
+ __genradix_objs_per_page(_radix), \
+ __genradix_obj_size(_radix) + \
+ __genradix_page_remainder(_radix)))

static inline void __genradix_iter_advance(struct genradix_iter *iter,
size_t obj_size)
@@ -203,6 +226,25 @@ static inline void __genradix_iter_advance(struct genradix_iter *iter,
#define genradix_iter_advance(_iter, _radix) \
__genradix_iter_advance(_iter, __genradix_obj_size(_radix))

+static inline void __genradix_iter_rewind(struct genradix_iter *iter,
+ size_t obj_size)
+{
+ if (iter->offset == 0 ||
+ iter->offset == SIZE_MAX) {
+ iter->offset = SIZE_MAX;
+ return;
+ }
+
+ if ((iter->offset & (PAGE_SIZE - 1)) == 0)
+ iter->offset -= PAGE_SIZE % obj_size;
+
+ iter->offset -= obj_size;
+ iter->pos--;
+}
+
+#define genradix_iter_rewind(_iter, _radix) \
+ __genradix_iter_rewind(_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; \
@@ -220,6 +262,23 @@ static inline void __genradix_iter_advance(struct genradix_iter *iter,
#define genradix_for_each(_radix, _iter, _p) \
genradix_for_each_from(_radix, _iter, _p, 0)

+#define genradix_last_pos(_radix) \
+ (SIZE_MAX / PAGE_SIZE * __genradix_objs_per_page(_radix) - 1)
+
+/**
+ * genradix_for_each_reverse - iterate over entry in a genradix, reverse order
+ * @_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_reverse(_radix, _iter, _p) \
+ for (_iter = genradix_iter_init(_radix, genradix_last_pos(_radix));\
+ (_p = genradix_iter_peek_prev(&_iter, _radix)) != NULL;\
+ genradix_iter_rewind(&_iter, _radix))
+
int __genradix_prealloc(struct __genradix *, size_t, gfp_t);

/**
diff --git a/lib/generic-radix-tree.c b/lib/generic-radix-tree.c
index 7dfa88282b..41f1bcdc44 100644
--- a/lib/generic-radix-tree.c
+++ b/lib/generic-radix-tree.c
@@ -1,4 +1,5 @@

+#include <linux/atomic.h>
#include <linux/export.h>
#include <linux/generic-radix-tree.h>
#include <linux/gfp.h>
@@ -212,6 +213,64 @@ void *__genradix_iter_peek(struct genradix_iter *iter,
}
EXPORT_SYMBOL(__genradix_iter_peek);

+void *__genradix_iter_peek_prev(struct genradix_iter *iter,
+ struct __genradix *radix,
+ size_t objs_per_page,
+ size_t obj_size_plus_page_remainder)
+{
+ struct genradix_root *r;
+ struct genradix_node *n;
+ unsigned level, i;
+
+ if (iter->offset == SIZE_MAX)
+ return NULL;
+
+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)) {
+ iter->offset = genradix_depth_size(level);
+ iter->pos = (iter->offset >> PAGE_SHIFT) * objs_per_page;
+
+ iter->offset -= obj_size_plus_page_remainder;
+ iter->pos--;
+ }
+
+ while (level) {
+ level--;
+
+ i = (iter->offset >> genradix_depth_shift(level)) &
+ (GENRADIX_ARY - 1);
+
+ while (!n->children[i]) {
+ size_t objs_per_ptr = genradix_depth_size(level);
+
+ iter->offset = round_down(iter->offset, objs_per_ptr);
+ iter->pos = (iter->offset >> PAGE_SHIFT) * objs_per_page;
+
+ if (!iter->offset)
+ return NULL;
+
+ iter->offset -= obj_size_plus_page_remainder;
+ iter->pos--;
+
+ if (!i)
+ goto restart;
+ --i;
+ }
+
+ n = n->children[i];
+ }
+
+ return &n->data[iter->offset & (PAGE_SIZE - 1)];
+}
+EXPORT_SYMBOL(__genradix_iter_peek_prev);
+
static void genradix_free_recurse(struct genradix_node *n, unsigned level)
{
if (level) {
--
2.40.1