2 * Fast and scalable bitmaps.
4 * Copyright (C) 2016 Facebook
5 * Copyright (C) 2013-2014 Jens Axboe
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public
9 * License v2 as published by the Free Software Foundation.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <https://www.gnu.org/licenses/>.
20 #ifndef __LINUX_SCALE_BITMAP_H
21 #define __LINUX_SCALE_BITMAP_H
23 #include <linux/kernel.h>
24 #include <linux/slab.h>
27 * struct sbitmap_word - Word in a &struct sbitmap.
31 * @word: The bitmap word itself.
36 * @depth: Number of bits being used in @word.
39 } ____cacheline_aligned_in_smp;
42 * struct sbitmap - Scalable bitmap.
44 * A &struct sbitmap is spread over multiple cachelines to avoid ping-pong. This
45 * trades off higher memory usage for better scalability.
49 * @depth: Number of bits used in the whole bitmap.
54 * @shift: log2(number of bits used per word)
59 * @map_nr: Number of words (cachelines) being used for the bitmap.
64 * @map: Allocated bitmap.
66 struct sbitmap_word *map;
69 #define SBQ_WAIT_QUEUES 8
70 #define SBQ_WAKE_BATCH 8
73 * struct sbq_wait_state - Wait queue in a &struct sbitmap_queue.
75 struct sbq_wait_state {
77 * @wait_cnt: Number of frees remaining before we wake up.
84 wait_queue_head_t wait;
85 } ____cacheline_aligned_in_smp;
88 * struct sbitmap_queue - Scalable bitmap with the added ability to wait on free
91 * A &struct sbitmap_queue uses multiple wait queues and rolling wakeups to
92 * avoid contention on the wait queue spinlock. This ensures that we don't hit a
93 * scalability wall when we run out of free bits and have to start putting tasks
96 struct sbitmap_queue {
98 * @sb: Scalable bitmap.
103 * @alloc_hint: Cache of last successfully allocated or freed bit.
105 * This is per-cpu, which allows multiple users to stick to different
106 * cachelines until the map is exhausted.
108 unsigned int __percpu *alloc_hint;
111 * @wake_batch: Number of bits which must be freed before we wake up any
114 unsigned int wake_batch;
117 * @wake_index: Next wait queue in @ws to wake up.
124 struct sbq_wait_state *ws;
127 * @round_robin: Allocate bits in strict round-robin order.
133 * sbitmap_init_node() - Initialize a &struct sbitmap on a specific memory node.
134 * @sb: Bitmap to initialize.
135 * @depth: Number of bits to allocate.
136 * @shift: Use 2^@shift bits per word in the bitmap; if a negative number if
137 * given, a good default is chosen.
138 * @flags: Allocation flags.
139 * @node: Memory node to allocate on.
141 * Return: Zero on success or negative errno on failure.
143 int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
144 gfp_t flags, int node);
147 * sbitmap_free() - Free memory used by a &struct sbitmap.
148 * @sb: Bitmap to free.
150 static inline void sbitmap_free(struct sbitmap *sb)
157 * sbitmap_resize() - Resize a &struct sbitmap.
158 * @sb: Bitmap to resize.
159 * @depth: New number of bits to resize to.
161 * Doesn't reallocate anything. It's up to the caller to ensure that the new
162 * depth doesn't exceed the depth that the sb was initialized with.
164 void sbitmap_resize(struct sbitmap *sb, unsigned int depth);
167 * sbitmap_get() - Try to allocate a free bit from a &struct sbitmap.
168 * @sb: Bitmap to allocate from.
169 * @alloc_hint: Hint for where to start searching for a free bit.
170 * @round_robin: If true, be stricter about allocation order; always allocate
171 * starting from the last allocated bit. This is less efficient
172 * than the default behavior (false).
174 * This operation provides acquire barrier semantics if it succeeds.
176 * Return: Non-negative allocated bit number if successful, -1 otherwise.
178 int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin);
181 * sbitmap_get_shallow() - Try to allocate a free bit from a &struct sbitmap,
182 * limiting the depth used from each word.
183 * @sb: Bitmap to allocate from.
184 * @alloc_hint: Hint for where to start searching for a free bit.
185 * @shallow_depth: The maximum number of bits to allocate from a single word.
187 * This rather specific operation allows for having multiple users with
188 * different allocation limits. E.g., there can be a high-priority class that
189 * uses sbitmap_get() and a low-priority class that uses sbitmap_get_shallow()
190 * with a @shallow_depth of (1 << (@sb->shift - 1)). Then, the low-priority
191 * class can only allocate half of the total bits in the bitmap, preventing it
192 * from starving out the high-priority class.
194 * Return: Non-negative allocated bit number if successful, -1 otherwise.
196 int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
197 unsigned long shallow_depth);
200 * sbitmap_any_bit_set() - Check for a set bit in a &struct sbitmap.
201 * @sb: Bitmap to check.
203 * Return: true if any bit in the bitmap is set, false otherwise.
205 bool sbitmap_any_bit_set(const struct sbitmap *sb);
208 * sbitmap_any_bit_clear() - Check for an unset bit in a &struct
210 * @sb: Bitmap to check.
212 * Return: true if any bit in the bitmap is clear, false otherwise.
214 bool sbitmap_any_bit_clear(const struct sbitmap *sb);
216 #define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
217 #define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
219 typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
222 * __sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
223 * @start: Where to start the iteration.
224 * @sb: Bitmap to iterate over.
225 * @fn: Callback. Should return true to continue or false to break early.
226 * @data: Pointer to pass to callback.
228 * This is inline even though it's non-trivial so that the function calls to the
229 * callback will hopefully get optimized away.
231 static inline void __sbitmap_for_each_set(struct sbitmap *sb,
233 sb_for_each_fn fn, void *data)
237 unsigned int scanned = 0;
239 if (start >= sb->depth)
241 index = SB_NR_TO_INDEX(sb, start);
242 nr = SB_NR_TO_BIT(sb, start);
244 while (scanned < sb->depth) {
245 struct sbitmap_word *word = &sb->map[index];
246 unsigned int depth = min_t(unsigned int, word->depth - nr,
247 sb->depth - scanned);
254 * On the first iteration of the outer loop, we need to add the
255 * bit offset back to the size of the word for find_next_bit().
256 * On all other iterations, nr is zero, so this is a noop.
260 nr = find_next_bit(&word->word, depth, nr);
263 if (!fn(sb, (index << sb->shift) + nr, data))
270 if (++index >= sb->map_nr)
276 * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
277 * @sb: Bitmap to iterate over.
278 * @fn: Callback. Should return true to continue or false to break early.
279 * @data: Pointer to pass to callback.
281 static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
284 __sbitmap_for_each_set(sb, 0, fn, data);
287 static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
290 return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
293 /* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
295 static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
297 set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
300 static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
302 clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
305 static inline void sbitmap_clear_bit_unlock(struct sbitmap *sb,
308 clear_bit_unlock(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
311 static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
313 return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
316 unsigned int sbitmap_weight(const struct sbitmap *sb);
319 * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file.
320 * @sb: Bitmap to show.
321 * @m: struct seq_file to write to.
323 * This is intended for debugging. The format may change at any time.
325 void sbitmap_show(struct sbitmap *sb, struct seq_file *m);
328 * sbitmap_bitmap_show() - Write a hex dump of a &struct sbitmap to a &struct
330 * @sb: Bitmap to show.
331 * @m: struct seq_file to write to.
333 * This is intended for debugging. The output isn't guaranteed to be internally
336 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m);
339 * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
341 * @sbq: Bitmap queue to initialize.
342 * @depth: See sbitmap_init_node().
343 * @shift: See sbitmap_init_node().
344 * @round_robin: See sbitmap_get().
345 * @flags: Allocation flags.
346 * @node: Memory node to allocate on.
348 * Return: Zero on success or negative errno on failure.
350 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
351 int shift, bool round_robin, gfp_t flags, int node);
354 * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
356 * @sbq: Bitmap queue to free.
358 static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
361 free_percpu(sbq->alloc_hint);
362 sbitmap_free(&sbq->sb);
366 * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
367 * @sbq: Bitmap queue to resize.
368 * @depth: New number of bits to resize to.
370 * Like sbitmap_resize(), this doesn't reallocate anything. It has to do
371 * some extra work on the &struct sbitmap_queue, so it's not safe to just
372 * resize the underlying &struct sbitmap.
374 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
377 * __sbitmap_queue_get() - Try to allocate a free bit from a &struct
378 * sbitmap_queue with preemption already disabled.
379 * @sbq: Bitmap queue to allocate from.
381 * Return: Non-negative allocated bit number if successful, -1 otherwise.
383 int __sbitmap_queue_get(struct sbitmap_queue *sbq);
386 * __sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
387 * sbitmap_queue, limiting the depth used from each word, with preemption
389 * @sbq: Bitmap queue to allocate from.
390 * @shallow_depth: The maximum number of bits to allocate from a single word.
391 * See sbitmap_get_shallow().
393 * Return: Non-negative allocated bit number if successful, -1 otherwise.
395 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
396 unsigned int shallow_depth);
399 * sbitmap_queue_get() - Try to allocate a free bit from a &struct
401 * @sbq: Bitmap queue to allocate from.
402 * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
403 * sbitmap_queue_clear()).
405 * Return: Non-negative allocated bit number if successful, -1 otherwise.
407 static inline int sbitmap_queue_get(struct sbitmap_queue *sbq,
413 nr = __sbitmap_queue_get(sbq);
419 * sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
420 * sbitmap_queue, limiting the depth used from each word.
421 * @sbq: Bitmap queue to allocate from.
422 * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
423 * sbitmap_queue_clear()).
424 * @shallow_depth: The maximum number of bits to allocate from a single word.
425 * See sbitmap_get_shallow().
427 * Return: Non-negative allocated bit number if successful, -1 otherwise.
429 static inline int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
431 unsigned int shallow_depth)
436 nr = __sbitmap_queue_get_shallow(sbq, shallow_depth);
442 * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
443 * &struct sbitmap_queue.
444 * @sbq: Bitmap to free from.
445 * @nr: Bit number to free.
446 * @cpu: CPU the bit was allocated on.
448 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
451 static inline int sbq_index_inc(int index)
453 return (index + 1) & (SBQ_WAIT_QUEUES - 1);
456 static inline void sbq_index_atomic_inc(atomic_t *index)
458 int old = atomic_read(index);
459 int new = sbq_index_inc(old);
460 atomic_cmpxchg(index, old, new);
464 * sbq_wait_ptr() - Get the next wait queue to use for a &struct
466 * @sbq: Bitmap queue to wait on.
467 * @wait_index: A counter per "user" of @sbq.
469 static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
470 atomic_t *wait_index)
472 struct sbq_wait_state *ws;
474 ws = &sbq->ws[atomic_read(wait_index)];
475 sbq_index_atomic_inc(wait_index);
480 * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
482 * @sbq: Bitmap queue to wake up.
484 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
487 * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
489 * @sbq: Bitmap queue to show.
490 * @m: struct seq_file to write to.
492 * This is intended for debugging. The format may change at any time.
494 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m);
496 #endif /* __LINUX_SCALE_BITMAP_H */