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