sbitmap.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * Fast and scalable bitmaps.
  4 *
  5 * Copyright (C) 2016 Facebook
  6 * Copyright (C) 2013-2014 Jens Axboe
  7 */
  8
  9#ifndef __LINUX_SCALE_BITMAP_H
 10#define __LINUX_SCALE_BITMAP_H
 11
 12#include <linux/atomic.h>
 13#include <linux/bitops.h>
 14#include <linux/cache.h>
 15#include <linux/list.h>
 16#include <linux/log2.h>
 17#include <linux/minmax.h>
 18#include <linux/percpu.h>
 19#include <linux/slab.h>
 20#include <linux/smp.h>
 21#include <linux/types.h>
 22#include <linux/wait.h>
 23
 24struct seq_file;
 25
 26/**
 27 * struct sbitmap_word - Word in a &struct sbitmap.
 28 */
 29struct sbitmap_word {
 30	/**
 31	 * @word: word holding free bits
 32	 */
 33	unsigned long word;
 34
 35	/**
 36	 * @cleared: word holding cleared bits
 37	 */
 38	unsigned long cleared ____cacheline_aligned_in_smp;
 39
 40	/**
 41	 * @swap_lock: serializes simultaneous updates of ->word and ->cleared
 42	 */
 43	raw_spinlock_t swap_lock;
 44} ____cacheline_aligned_in_smp;
 45
 46/**
 47 * struct sbitmap - Scalable bitmap.
 48 *
 49 * A &struct sbitmap is spread over multiple cachelines to avoid ping-pong. This
 50 * trades off higher memory usage for better scalability.
 51 */
 52struct sbitmap {
 53	/**
 54	 * @depth: Number of bits used in the whole bitmap.
 55	 */
 56	unsigned int depth;
 57
 58	/**
 59	 * @shift: log2(number of bits used per word)
 60	 */
 61	unsigned int shift;
 62
 63	/**
 64	 * @map_nr: Number of words (cachelines) being used for the bitmap.
 65	 */
 66	unsigned int map_nr;
 67
 68	/**
 69	 * @round_robin: Allocate bits in strict round-robin order.
 70	 */
 71	bool round_robin;
 72
 73	/**
 74	 * @map: Allocated bitmap.
 75	 */
 76	struct sbitmap_word *map;
 77
 78	/**
 79	 * @alloc_hint: Cache of last successfully allocated or freed bit.
 80	 *
 81	 * This is per-cpu, which allows multiple users to stick to different
 82	 * cachelines until the map is exhausted.
 83	 */
 84	unsigned int __percpu *alloc_hint;
 85};
 86
 87#define SBQ_WAIT_QUEUES 8
 88#define SBQ_WAKE_BATCH 8
 89
 90/**
 91 * struct sbq_wait_state - Wait queue in a &struct sbitmap_queue.
 92 */
 93struct sbq_wait_state {
 94	/**
 95	 * @wait: Wait queue.
 96	 */
 97	wait_queue_head_t wait;
 98} ____cacheline_aligned_in_smp;
 99
100/**
101 * struct sbitmap_queue - Scalable bitmap with the added ability to wait on free
102 * bits.
103 *
104 * A &struct sbitmap_queue uses multiple wait queues and rolling wakeups to
105 * avoid contention on the wait queue spinlock. This ensures that we don't hit a
106 * scalability wall when we run out of free bits and have to start putting tasks
107 * to sleep.
108 */
109struct sbitmap_queue {
110	/**
111	 * @sb: Scalable bitmap.
112	 */
113	struct sbitmap sb;
114
115	/**
116	 * @wake_batch: Number of bits which must be freed before we wake up any
117	 * waiters.
118	 */
119	unsigned int wake_batch;
120
121	/**
122	 * @wake_index: Next wait queue in @ws to wake up.
123	 */
124	atomic_t wake_index;
125
126	/**
127	 * @ws: Wait queues.
128	 */
129	struct sbq_wait_state *ws;
130
131	/**
132	 * @ws_active: count of currently active ws waitqueues
133	 */
134	atomic_t ws_active;
135
136	/**
137	 * @min_shallow_depth: The minimum shallow depth which may be passed to
138	 * sbitmap_queue_get_shallow()
139	 */
140	unsigned int min_shallow_depth;
141
142	/**
143	 * @completion_cnt: Number of bits cleared passed to the
144	 * wakeup function.
145	 */
146	atomic_t completion_cnt;
147
148	/**
149	 * @wakeup_cnt: Number of thread wake ups issued.
150	 */
151	atomic_t wakeup_cnt;
152};
153
154/**
155 * sbitmap_init_node() - Initialize a &struct sbitmap on a specific memory node.
156 * @sb: Bitmap to initialize.
157 * @depth: Number of bits to allocate.
158 * @shift: Use 2^@shift bits per word in the bitmap; if a negative number if
159 *         given, a good default is chosen.
160 * @flags: Allocation flags.
161 * @node: Memory node to allocate on.
162 * @round_robin: If true, be stricter about allocation order; always allocate
163 *               starting from the last allocated bit. This is less efficient
164 *               than the default behavior (false).
165 * @alloc_hint: If true, apply percpu hint for where to start searching for
166 *              a free bit.
167 *
168 * Return: Zero on success or negative errno on failure.
169 */
170int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
171		      gfp_t flags, int node, bool round_robin, bool alloc_hint);
172
173/* sbitmap internal helper */
174static inline unsigned int __map_depth(const struct sbitmap *sb, int index)
175{
176	if (index == sb->map_nr - 1)
177		return sb->depth - (index << sb->shift);
178	return 1U << sb->shift;
179}
180
181/**
182 * sbitmap_free() - Free memory used by a &struct sbitmap.
183 * @sb: Bitmap to free.
184 */
185static inline void sbitmap_free(struct sbitmap *sb)
186{
187	free_percpu(sb->alloc_hint);
188	kvfree(sb->map);
189	sb->map = NULL;
190}
191
192/**
193 * sbitmap_resize() - Resize a &struct sbitmap.
194 * @sb: Bitmap to resize.
195 * @depth: New number of bits to resize to.
196 *
197 * Doesn't reallocate anything. It's up to the caller to ensure that the new
198 * depth doesn't exceed the depth that the sb was initialized with.
199 */
200void sbitmap_resize(struct sbitmap *sb, unsigned int depth);
201
202/**
203 * sbitmap_get() - Try to allocate a free bit from a &struct sbitmap.
204 * @sb: Bitmap to allocate from.
205 *
206 * This operation provides acquire barrier semantics if it succeeds.
207 *
208 * Return: Non-negative allocated bit number if successful, -1 otherwise.
209 */
210int sbitmap_get(struct sbitmap *sb);
211
212/**
213 * sbitmap_any_bit_set() - Check for a set bit in a &struct sbitmap.
214 * @sb: Bitmap to check.
215 *
216 * Return: true if any bit in the bitmap is set, false otherwise.
217 */
218bool sbitmap_any_bit_set(const struct sbitmap *sb);
219
220#define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
221#define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
222
223typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
224
225/**
226 * __sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
227 * @start: Where to start the iteration.
228 * @sb: Bitmap to iterate over.
229 * @fn: Callback. Should return true to continue or false to break early.
230 * @data: Pointer to pass to callback.
231 *
232 * This is inline even though it's non-trivial so that the function calls to the
233 * callback will hopefully get optimized away.
234 */
235static inline void __sbitmap_for_each_set(struct sbitmap *sb,
236					  unsigned int start,
237					  sb_for_each_fn fn, void *data)
238{
239	unsigned int index;
240	unsigned int nr;
241	unsigned int scanned = 0;
242
243	if (start >= sb->depth)
244		start = 0;
245	index = SB_NR_TO_INDEX(sb, start);
246	nr = SB_NR_TO_BIT(sb, start);
247
248	while (scanned < sb->depth) {
249		unsigned long word;
250		unsigned int depth = min_t(unsigned int,
251					   __map_depth(sb, index) - nr,
252					   sb->depth - scanned);
253
254		scanned += depth;
255		word = sb->map[index].word & ~sb->map[index].cleared;
256		if (!word)
257			goto next;
258
259		/*
260		 * On the first iteration of the outer loop, we need to add the
261		 * bit offset back to the size of the word for find_next_bit().
262		 * On all other iterations, nr is zero, so this is a noop.
263		 */
264		depth += nr;
265		while (1) {
266			nr = find_next_bit(&word, depth, nr);
267			if (nr >= depth)
268				break;
269			if (!fn(sb, (index << sb->shift) + nr, data))
270				return;
271
272			nr++;
273		}
274next:
275		nr = 0;
276		if (++index >= sb->map_nr)
277			index = 0;
278	}
279}
280
281/**
282 * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
283 * @sb: Bitmap to iterate over.
284 * @fn: Callback. Should return true to continue or false to break early.
285 * @data: Pointer to pass to callback.
286 */
287static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
288					void *data)
289{
290	__sbitmap_for_each_set(sb, 0, fn, data);
291}
292
293static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
294					    unsigned int bitnr)
295{
296	return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
297}
298
299/* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
300
301static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
302{
303	set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
304}
305
306static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
307{
308	clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
309}
310
311/*
312 * This one is special, since it doesn't actually clear the bit, rather it
313 * sets the corresponding bit in the ->cleared mask instead. Paired with
314 * the caller doing sbitmap_deferred_clear() if a given index is full, which
315 * will clear the previously freed entries in the corresponding ->word.
316 */
317static inline void sbitmap_deferred_clear_bit(struct sbitmap *sb, unsigned int bitnr)
318{
319	unsigned long *addr = &sb->map[SB_NR_TO_INDEX(sb, bitnr)].cleared;
320
321	set_bit(SB_NR_TO_BIT(sb, bitnr), addr);
322}
323
324/*
325 * Pair of sbitmap_get, and this one applies both cleared bit and
326 * allocation hint.
327 */
328static inline void sbitmap_put(struct sbitmap *sb, unsigned int bitnr)
329{
330	sbitmap_deferred_clear_bit(sb, bitnr);
331
332	if (likely(sb->alloc_hint && !sb->round_robin && bitnr < sb->depth))
333		*raw_cpu_ptr(sb->alloc_hint) = bitnr;
334}
335
336static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
337{
338	return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
339}
340
341static inline int sbitmap_calculate_shift(unsigned int depth)
342{
343	int	shift = ilog2(BITS_PER_LONG);
344
345	/*
346	 * If the bitmap is small, shrink the number of bits per word so
347	 * we spread over a few cachelines, at least. If less than 4
348	 * bits, just forget about it, it's not going to work optimally
349	 * anyway.
350	 */
351	if (depth >= 4) {
352		while ((4U << shift) > depth)
353			shift--;
354	}
355
356	return shift;
357}
358
359/**
360 * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file.
361 * @sb: Bitmap to show.
362 * @m: struct seq_file to write to.
363 *
364 * This is intended for debugging. The format may change at any time.
365 */
366void sbitmap_show(struct sbitmap *sb, struct seq_file *m);
367
368
369/**
370 * sbitmap_weight() - Return how many set and not cleared bits in a &struct
371 * sbitmap.
372 * @sb: Bitmap to check.
373 *
374 * Return: How many set and not cleared bits set
375 */
376unsigned int sbitmap_weight(const struct sbitmap *sb);
377
378/**
379 * sbitmap_bitmap_show() - Write a hex dump of a &struct sbitmap to a &struct
380 * seq_file.
381 * @sb: Bitmap to show.
382 * @m: struct seq_file to write to.
383 *
384 * This is intended for debugging. The output isn't guaranteed to be internally
385 * consistent.
386 */
387void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m);
388
389/**
390 * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
391 * memory node.
392 * @sbq: Bitmap queue to initialize.
393 * @depth: See sbitmap_init_node().
394 * @shift: See sbitmap_init_node().
395 * @round_robin: See sbitmap_get().
396 * @flags: Allocation flags.
397 * @node: Memory node to allocate on.
398 *
399 * Return: Zero on success or negative errno on failure.
400 */
401int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
402			    int shift, bool round_robin, gfp_t flags, int node);
403
404/**
405 * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
406 *
407 * @sbq: Bitmap queue to free.
408 */
409static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
410{
411	kfree(sbq->ws);
412	sbitmap_free(&sbq->sb);
413}
414
415/**
416 * sbitmap_queue_recalculate_wake_batch() - Recalculate wake batch
417 * @sbq: Bitmap queue to recalculate wake batch.
418 * @users: Number of shares.
419 *
420 * Like sbitmap_queue_update_wake_batch(), this will calculate wake batch
421 * by depth. This interface is for HCTX shared tags or queue shared tags.
422 */
423void sbitmap_queue_recalculate_wake_batch(struct sbitmap_queue *sbq,
424					    unsigned int users);
425
426/**
427 * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
428 * @sbq: Bitmap queue to resize.
429 * @depth: New number of bits to resize to.
430 *
431 * Like sbitmap_resize(), this doesn't reallocate anything. It has to do
432 * some extra work on the &struct sbitmap_queue, so it's not safe to just
433 * resize the underlying &struct sbitmap.
434 */
435void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
436
437/**
438 * __sbitmap_queue_get() - Try to allocate a free bit from a &struct
439 * sbitmap_queue with preemption already disabled.
440 * @sbq: Bitmap queue to allocate from.
441 *
442 * Return: Non-negative allocated bit number if successful, -1 otherwise.
443 */
444int __sbitmap_queue_get(struct sbitmap_queue *sbq);
445
446/**
447 * __sbitmap_queue_get_batch() - Try to allocate a batch of free bits
448 * @sbq: Bitmap queue to allocate from.
449 * @nr_tags: number of tags requested
450 * @offset: offset to add to returned bits
451 *
452 * Return: Mask of allocated tags, 0 if none are found. Each tag allocated is
453 * a bit in the mask returned, and the caller must add @offset to the value to
454 * get the absolute tag value.
455 */
456unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
457					unsigned int *offset);
458
459/**
460 * sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
461 * sbitmap_queue, limiting the depth used from each word, with preemption
462 * already disabled.
463 * @sbq: Bitmap queue to allocate from.
464 * @shallow_depth: The maximum number of bits to allocate from the queue.
465 * See sbitmap_get_shallow().
466 *
467 * If you call this, make sure to call sbitmap_queue_min_shallow_depth() after
468 * initializing @sbq.
469 *
470 * Return: Non-negative allocated bit number if successful, -1 otherwise.
471 */
472int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
473			      unsigned int shallow_depth);
474
475/**
476 * sbitmap_queue_get() - Try to allocate a free bit from a &struct
477 * sbitmap_queue.
478 * @sbq: Bitmap queue to allocate from.
479 * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
480 *       sbitmap_queue_clear()).
481 *
482 * Return: Non-negative allocated bit number if successful, -1 otherwise.
483 */
484static inline int sbitmap_queue_get(struct sbitmap_queue *sbq,
485				    unsigned int *cpu)
486{
487	int nr;
488
489	*cpu = get_cpu();
490	nr = __sbitmap_queue_get(sbq);
491	put_cpu();
492	return nr;
493}
494
495/**
496 * sbitmap_queue_min_shallow_depth() - Inform a &struct sbitmap_queue of the
497 * minimum shallow depth that will be used.
498 * @sbq: Bitmap queue in question.
499 * @min_shallow_depth: The minimum shallow depth that will be passed to
500 * sbitmap_queue_get_shallow() or __sbitmap_queue_get_shallow().
501 *
502 * sbitmap_queue_clear() batches wakeups as an optimization. The batch size
503 * depends on the depth of the bitmap. Since the shallow allocation functions
504 * effectively operate with a different depth, the shallow depth must be taken
505 * into account when calculating the batch size. This function must be called
506 * with the minimum shallow depth that will be used. Failure to do so can result
507 * in missed wakeups.
508 */
509void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
510				     unsigned int min_shallow_depth);
511
512/**
513 * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
514 * &struct sbitmap_queue.
515 * @sbq: Bitmap to free from.
516 * @nr: Bit number to free.
517 * @cpu: CPU the bit was allocated on.
518 */
519void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
520			 unsigned int cpu);
521
522/**
523 * sbitmap_queue_clear_batch() - Free a batch of allocated bits
524 * &struct sbitmap_queue.
525 * @sbq: Bitmap to free from.
526 * @offset: offset for each tag in array
527 * @tags: array of tags
528 * @nr_tags: number of tags in array
529 */
530void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
531				int *tags, int nr_tags);
532
533static inline int sbq_index_inc(int index)
534{
535	return (index + 1) & (SBQ_WAIT_QUEUES - 1);
536}
537
538static inline void sbq_index_atomic_inc(atomic_t *index)
539{
540	int old = atomic_read(index);
541	int new = sbq_index_inc(old);
542	atomic_cmpxchg(index, old, new);
543}
544
545/**
546 * sbq_wait_ptr() - Get the next wait queue to use for a &struct
547 * sbitmap_queue.
548 * @sbq: Bitmap queue to wait on.
549 * @wait_index: A counter per "user" of @sbq.
550 *
551 * Return: Next wait queue to be used
552 */
553static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
554						  atomic_t *wait_index)
555{
556	struct sbq_wait_state *ws;
557
558	ws = &sbq->ws[atomic_read(wait_index)];
559	sbq_index_atomic_inc(wait_index);
560	return ws;
561}
562
563/**
564 * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
565 * sbitmap_queue.
566 * @sbq: Bitmap queue to wake up.
567 */
568void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
569
570/**
571 * sbitmap_queue_wake_up() - Wake up some of waiters in one waitqueue
572 * on a &struct sbitmap_queue.
573 * @sbq: Bitmap queue to wake up.
574 * @nr: Number of bits cleared.
575 */
576void sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr);
577
578/**
579 * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
580 * seq_file.
581 * @sbq: Bitmap queue to show.
582 * @m: struct seq_file to write to.
583 *
584 * This is intended for debugging. The format may change at any time.
585 */
586void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m);
587
588struct sbq_wait {
589	struct sbitmap_queue *sbq;	/* if set, sbq_wait is accounted */
590	struct wait_queue_entry wait;
591};
592
593#define DEFINE_SBQ_WAIT(name)							\
594	struct sbq_wait name = {						\
595		.sbq = NULL,							\
596		.wait = {							\
597			.private	= current,				\
598			.func		= autoremove_wake_function,		\
599			.entry		= LIST_HEAD_INIT((name).wait.entry),	\
600		}								\
601	}
602
603/*
604 * Wrapper around prepare_to_wait_exclusive(), which maintains some extra
605 * internal state.
606 */
607void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
608				struct sbq_wait_state *ws,
609				struct sbq_wait *sbq_wait, int state);
610
611/*
612 * Must be paired with sbitmap_prepare_to_wait().
613 */
614void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
615				struct sbq_wait *sbq_wait);
616
617/*
618 * Wrapper around add_wait_queue(), which maintains some extra internal state
619 */
620void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
621			    struct sbq_wait_state *ws,
622			    struct sbq_wait *sbq_wait);
623
624/*
625 * Must be paired with sbitmap_add_wait_queue()
626 */
627void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait);
628
629#endif /* __LINUX_SCALE_BITMAP_H */