1 /*
2 * Fast and scalable bitmaps.
3 *
4 * Copyright (C) 2016 Facebook
5 * Copyright (C) 2013-2014 Jens Axboe
6 *
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.
10 *
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.
15 *
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/>.
18 */
19
20 #ifndef __LINUX_SCALE_BITMAP_H
21 #define __LINUX_SCALE_BITMAP_H
22
23 #include <linux/kernel.h>
24 #include <linux/slab.h>
25
26 /**
27 * struct sbitmap_word - Word in a &struct sbitmap.
28 */
29 struct sbitmap_word {
30 /**
31 * @word: The bitmap word itself.
32 */
33 unsigned long word;
34
35 /**
36 * @depth: Number of bits being used in @word.
37 */
38 unsigned long depth;
39 } ____cacheline_aligned_in_smp;
40
41 /**
42 * struct sbitmap - Scalable bitmap.
43 *
44 * A &struct sbitmap is spread over multiple cachelines to avoid ping-pong. This
45 * trades off higher memory usage for better scalability.
46 */
47 struct sbitmap {
48 /**
49 * @depth: Number of bits used in the whole bitmap.
50 */
51 unsigned int depth;
52
53 /**
54 * @shift: log2(number of bits used per word)
55 */
56 unsigned int shift;
57
58 /**
59 * @map_nr: Number of words (cachelines) being used for the bitmap.
60 */
61 unsigned int map_nr;
62
63 /**
64 * @map: Allocated bitmap.
65 */
66 struct sbitmap_word *map;
67 };
68
69 #define SBQ_WAIT_QUEUES 8
70 #define SBQ_WAKE_BATCH 8
71
72 /**
73 * struct sbq_wait_state - Wait queue in a &struct sbitmap_queue.
74 */
75 struct sbq_wait_state {
76 /**
77 * @wait_cnt: Number of frees remaining before we wake up.
78 */
79 atomic_t wait_cnt;
80
81 /**
82 * @wait: Wait queue.
83 */
84 wait_queue_head_t wait;
85 } ____cacheline_aligned_in_smp;
86
87 /**
88 * struct sbitmap_queue - Scalable bitmap with the added ability to wait on free
89 * bits.
90 *
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
94 * to sleep.
95 */
96 struct sbitmap_queue {
97 /**
98 * @sb: Scalable bitmap.
99 */
100 struct sbitmap sb;
101
102 /*
103 * @alloc_hint: Cache of last successfully allocated or freed bit.
104 *
105 * This is per-cpu, which allows multiple users to stick to different
106 * cachelines until the map is exhausted.
107 */
108 unsigned int __percpu *alloc_hint;
109
110 /**
111 * @wake_batch: Number of bits which must be freed before we wake up any
112 * waiters.
113 */
114 unsigned int wake_batch;
115
116 /**
117 * @wake_index: Next wait queue in @ws to wake up.
118 */
119 atomic_t wake_index;
120
121 /**
122 * @ws: Wait queues.
123 */
124 struct sbq_wait_state *ws;
125
126 /**
127 * @round_robin: Allocate bits in strict round-robin order.
128 */
129 bool round_robin;
130 };
131
132 /**
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.
140 *
141 * Return: Zero on success or negative errno on failure.
142 */
143 int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
144 gfp_t flags, int node);
145
146 /**
147 * sbitmap_free() - Free memory used by a &struct sbitmap.
148 * @sb: Bitmap to free.
149 */
150 static inline void sbitmap_free(struct sbitmap *sb)
151 {
152 kfree(sb->map);
153 sb->map = NULL;
154 }
155
156 /**
157 * sbitmap_resize() - Resize a &struct sbitmap.
158 * @sb: Bitmap to resize.
159 * @depth: New number of bits to resize to.
160 *
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.
163 */
164 void sbitmap_resize(struct sbitmap *sb, unsigned int depth);
165
166 /**
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).
173 *
174 * Return: Non-negative allocated bit number if successful, -1 otherwise.
175 */
176 int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin);
177
178 /**
179 * sbitmap_get_shallow() - Try to allocate a free bit from a &struct sbitmap,
180 * limiting the depth used from each word.
181 * @sb: Bitmap to allocate from.
182 * @alloc_hint: Hint for where to start searching for a free bit.
183 * @shallow_depth: The maximum number of bits to allocate from a single word.
184 *
185 * This rather specific operation allows for having multiple users with
186 * different allocation limits. E.g., there can be a high-priority class that
187 * uses sbitmap_get() and a low-priority class that uses sbitmap_get_shallow()
188 * with a @shallow_depth of (1 << (@sb->shift - 1)). Then, the low-priority
189 * class can only allocate half of the total bits in the bitmap, preventing it
190 * from starving out the high-priority class.
191 *
192 * Return: Non-negative allocated bit number if successful, -1 otherwise.
193 */
194 int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
195 unsigned long shallow_depth);
196
197 /**
198 * sbitmap_any_bit_set() - Check for a set bit in a &struct sbitmap.
199 * @sb: Bitmap to check.
200 *
201 * Return: true if any bit in the bitmap is set, false otherwise.
202 */
203 bool sbitmap_any_bit_set(const struct sbitmap *sb);
204
205 /**
206 * sbitmap_any_bit_clear() - Check for an unset bit in a &struct
207 * sbitmap.
208 * @sb: Bitmap to check.
209 *
210 * Return: true if any bit in the bitmap is clear, false otherwise.
211 */
212 bool sbitmap_any_bit_clear(const struct sbitmap *sb);
213
214 typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
215
216 /**
217 * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
218 * @sb: Bitmap to iterate over.
219 * @fn: Callback. Should return true to continue or false to break early.
220 * @data: Pointer to pass to callback.
221 *
222 * This is inline even though it's non-trivial so that the function calls to the
223 * callback will hopefully get optimized away.
224 */
225 static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
226 void *data)
227 {
228 unsigned int i;
229
230 for (i = 0; i < sb->map_nr; i++) {
231 struct sbitmap_word *word = &sb->map[i];
232 unsigned int off, nr;
233
234 if (!word->word)
235 continue;
236
237 nr = 0;
238 off = i << sb->shift;
239 while (1) {
240 nr = find_next_bit(&word->word, word->depth, nr);
241 if (nr >= word->depth)
242 break;
243
244 if (!fn(sb, off + nr, data))
245 return;
246
247 nr++;
248 }
249 }
250 }
251
252 #define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
253 #define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
254
255 static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
256 unsigned int bitnr)
257 {
258 return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
259 }
260
261 /* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
262
263 static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
264 {
265 set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
266 }
267
268 static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
269 {
270 clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
271 }
272
273 static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
274 {
275 return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
276 }
277
278 unsigned int sbitmap_weight(const struct sbitmap *sb);
279
280 /**
281 * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file.
282 * @sb: Bitmap to show.
283 * @m: struct seq_file to write to.
284 *
285 * This is intended for debugging. The format may change at any time.
286 */
287 void sbitmap_show(struct sbitmap *sb, struct seq_file *m);
288
289 /**
290 * sbitmap_bitmap_show() - Write a hex dump of a &struct sbitmap to a &struct
291 * seq_file.
292 * @sb: Bitmap to show.
293 * @m: struct seq_file to write to.
294 *
295 * This is intended for debugging. The output isn't guaranteed to be internally
296 * consistent.
297 */
298 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m);
299
300 /**
301 * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
302 * memory node.
303 * @sbq: Bitmap queue to initialize.
304 * @depth: See sbitmap_init_node().
305 * @shift: See sbitmap_init_node().
306 * @round_robin: See sbitmap_get().
307 * @flags: Allocation flags.
308 * @node: Memory node to allocate on.
309 *
310 * Return: Zero on success or negative errno on failure.
311 */
312 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
313 int shift, bool round_robin, gfp_t flags, int node);
314
315 /**
316 * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
317 *
318 * @sbq: Bitmap queue to free.
319 */
320 static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
321 {
322 kfree(sbq->ws);
323 free_percpu(sbq->alloc_hint);
324 sbitmap_free(&sbq->sb);
325 }
326
327 /**
328 * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
329 * @sbq: Bitmap queue to resize.
330 * @depth: New number of bits to resize to.
331 *
332 * Like sbitmap_resize(), this doesn't reallocate anything. It has to do
333 * some extra work on the &struct sbitmap_queue, so it's not safe to just
334 * resize the underlying &struct sbitmap.
335 */
336 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
337
338 /**
339 * __sbitmap_queue_get() - Try to allocate a free bit from a &struct
340 * sbitmap_queue with preemption already disabled.
341 * @sbq: Bitmap queue to allocate from.
342 *
343 * Return: Non-negative allocated bit number if successful, -1 otherwise.
344 */
345 int __sbitmap_queue_get(struct sbitmap_queue *sbq);
346
347 /**
348 * __sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
349 * sbitmap_queue, limiting the depth used from each word, with preemption
350 * already disabled.
351 * @sbq: Bitmap queue to allocate from.
352 * @shallow_depth: The maximum number of bits to allocate from a single word.
353 * See sbitmap_get_shallow().
354 *
355 * Return: Non-negative allocated bit number if successful, -1 otherwise.
356 */
357 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
358 unsigned int shallow_depth);
359
360 /**
361 * sbitmap_queue_get() - Try to allocate a free bit from a &struct
362 * sbitmap_queue.
363 * @sbq: Bitmap queue to allocate from.
364 * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
365 * sbitmap_queue_clear()).
366 *
367 * Return: Non-negative allocated bit number if successful, -1 otherwise.
368 */
369 static inline int sbitmap_queue_get(struct sbitmap_queue *sbq,
370 unsigned int *cpu)
371 {
372 int nr;
373
374 *cpu = get_cpu();
375 nr = __sbitmap_queue_get(sbq);
376 put_cpu();
377 return nr;
378 }
379
380 /**
381 * sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
382 * sbitmap_queue, limiting the depth used from each word.
383 * @sbq: Bitmap queue to allocate from.
384 * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
385 * sbitmap_queue_clear()).
386 * @shallow_depth: The maximum number of bits to allocate from a single word.
387 * See sbitmap_get_shallow().
388 *
389 * Return: Non-negative allocated bit number if successful, -1 otherwise.
390 */
391 static inline int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
392 unsigned int *cpu,
393 unsigned int shallow_depth)
394 {
395 int nr;
396
397 *cpu = get_cpu();
398 nr = __sbitmap_queue_get_shallow(sbq, shallow_depth);
399 put_cpu();
400 return nr;
401 }
402
403 /**
404 * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
405 * &struct sbitmap_queue.
406 * @sbq: Bitmap to free from.
407 * @nr: Bit number to free.
408 * @cpu: CPU the bit was allocated on.
409 */
410 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
411 unsigned int cpu);
412
413 static inline int sbq_index_inc(int index)
414 {
415 return (index + 1) & (SBQ_WAIT_QUEUES - 1);
416 }
417
418 static inline void sbq_index_atomic_inc(atomic_t *index)
419 {
420 int old = atomic_read(index);
421 int new = sbq_index_inc(old);
422 atomic_cmpxchg(index, old, new);
423 }
424
425 /**
426 * sbq_wait_ptr() - Get the next wait queue to use for a &struct
427 * sbitmap_queue.
428 * @sbq: Bitmap queue to wait on.
429 * @wait_index: A counter per "user" of @sbq.
430 */
431 static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
432 atomic_t *wait_index)
433 {
434 struct sbq_wait_state *ws;
435
436 ws = &sbq->ws[atomic_read(wait_index)];
437 sbq_index_atomic_inc(wait_index);
438 return ws;
439 }
440
441 /**
442 * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
443 * sbitmap_queue.
444 * @sbq: Bitmap queue to wake up.
445 */
446 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
447
448 /**
449 * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
450 * seq_file.
451 * @sbq: Bitmap queue to show.
452 * @m: struct seq_file to write to.
453 *
454 * This is intended for debugging. The format may change at any time.
455 */
456 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m);
457
458 #endif /* __LINUX_SCALE_BITMAP_H */
459
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