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Linux/include/linux/sbitmap.h

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

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