include/linux/sbitmap.h

   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 #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                 struct sbitmap_word *word = &sb->map[index];
 244                 unsigned int depth = min_t(unsigned int, word->depth - nr,
 245                                            sb->depth - scanned);
 246
 247                 scanned += depth;
 248                 if (!word->word)
 249                         goto next;
 250
 251                 /*
 252                  * On the first iteration of the outer loop, we need to add the
 253                  * bit offset back to the size of the word for find_next_bit().
 254                  * On all other iterations, nr is zero, so this is a noop.
 255                  */
 256                 depth += nr;
 257                 while (1) {
 258                         nr = find_next_bit(&word->word, depth, nr);
 259                         if (nr >= depth)
 260                                 break;
 261                         if (!fn(sb, (index << sb->shift) + nr, data))
 262                                 return;
 263
 264                         nr++;
 265                 }
 266 next:
 267                 nr = 0;
 268                 if (++index >= sb->map_nr)
 269                         index = 0;
 270         }
 271 }
 272
 273 /**
 274  * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
 275  * @sb: Bitmap to iterate over.
 276  * @fn: Callback. Should return true to continue or false to break early.
 277  * @data: Pointer to pass to callback.
 278  */
 279 static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
 280                                         void *data)
 281 {
 282         __sbitmap_for_each_set(sb, 0, fn, data);
 283 }
 284
 285 static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
 286                                             unsigned int bitnr)
 287 {
 288         return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
 289 }
 290
 291 /* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
 292
 293 static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
 294 {
 295         set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 296 }
 297
 298 static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
 299 {
 300         clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 301 }
 302
 303 static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
 304 {
 305         return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 306 }
 307
 308 unsigned int sbitmap_weight(const struct sbitmap *sb);
 309
 310 /**
 311  * sbitmap_show() - Dump &struct sbitmap information to a &struct seq_file.
 312  * @sb: Bitmap to show.
 313  * @m: struct seq_file to write to.
 314  *
 315  * This is intended for debugging. The format may change at any time.
 316  */
 317 void sbitmap_show(struct sbitmap *sb, struct seq_file *m);
 318
 319 /**
 320  * sbitmap_bitmap_show() - Write a hex dump of a &struct sbitmap to a &struct
 321  * seq_file.
 322  * @sb: Bitmap to show.
 323  * @m: struct seq_file to write to.
 324  *
 325  * This is intended for debugging. The output isn't guaranteed to be internally
 326  * consistent.
 327  */
 328 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m);
 329
 330 /**
 331  * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
 332  * memory node.
 333  * @sbq: Bitmap queue to initialize.
 334  * @depth: See sbitmap_init_node().
 335  * @shift: See sbitmap_init_node().
 336  * @round_robin: See sbitmap_get().
 337  * @flags: Allocation flags.
 338  * @node: Memory node to allocate on.
 339  *
 340  * Return: Zero on success or negative errno on failure.
 341  */
 342 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 343                             int shift, bool round_robin, gfp_t flags, int node);
 344
 345 /**
 346  * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
 347  *
 348  * @sbq: Bitmap queue to free.
 349  */
 350 static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
 351 {
 352         kfree(sbq->ws);
 353         free_percpu(sbq->alloc_hint);
 354         sbitmap_free(&sbq->sb);
 355 }
 356
 357 /**
 358  * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
 359  * @sbq: Bitmap queue to resize.
 360  * @depth: New number of bits to resize to.
 361  *
 362  * Like sbitmap_resize(), this doesn't reallocate anything. It has to do
 363  * some extra work on the &struct sbitmap_queue, so it's not safe to just
 364  * resize the underlying &struct sbitmap.
 365  */
 366 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
 367
 368 /**
 369  * __sbitmap_queue_get() - Try to allocate a free bit from a &struct
 370  * sbitmap_queue with preemption already disabled.
 371  * @sbq: Bitmap queue to allocate from.
 372  *
 373  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 374  */
 375 int __sbitmap_queue_get(struct sbitmap_queue *sbq);
 376
 377 /**
 378  * __sbitmap_queue_get_shallow() - Try to allocate a free bit from a &struct
 379  * sbitmap_queue, limiting the depth used from each word, with preemption
 380  * already disabled.
 381  * @sbq: Bitmap queue to allocate from.
 382  * @shallow_depth: The maximum number of bits to allocate from a single word.
 383  * See sbitmap_get_shallow().
 384  *
 385  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 386  */
 387 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
 388                                 unsigned int shallow_depth);
 389
 390 /**
 391  * sbitmap_queue_get() - Try to allocate a free bit from a &struct
 392  * sbitmap_queue.
 393  * @sbq: Bitmap queue to allocate from.
 394  * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
 395  *       sbitmap_queue_clear()).
 396  *
 397  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 398  */
 399 static inline int sbitmap_queue_get(struct sbitmap_queue *sbq,
 400                                     unsigned int *cpu)
 401 {
 402         int nr;
 403
 404         *cpu = get_cpu();
 405         nr = __sbitmap_queue_get(sbq);
 406         put_cpu();
 407         return nr;
 408 }
 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.
 413  * @sbq: Bitmap queue to allocate from.
 414  * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
 415  *       sbitmap_queue_clear()).
 416  * @shallow_depth: The maximum number of bits to allocate from a single word.
 417  * See sbitmap_get_shallow().
 418  *
 419  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 420  */
 421 static inline int sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
 422                                             unsigned int *cpu,
 423                                             unsigned int shallow_depth)
 424 {
 425         int nr;
 426
 427         *cpu = get_cpu();
 428         nr = __sbitmap_queue_get_shallow(sbq, shallow_depth);
 429         put_cpu();
 430         return nr;
 431 }
 432
 433 /**
 434  * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
 435  * &struct sbitmap_queue.
 436  * @sbq: Bitmap to free from.
 437  * @nr: Bit number to free.
 438  * @cpu: CPU the bit was allocated on.
 439  */
 440 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 441                          unsigned int cpu);
 442
 443 static inline int sbq_index_inc(int index)
 444 {
 445         return (index + 1) & (SBQ_WAIT_QUEUES - 1);
 446 }
 447
 448 static inline void sbq_index_atomic_inc(atomic_t *index)
 449 {
 450         int old = atomic_read(index);
 451         int new = sbq_index_inc(old);
 452         atomic_cmpxchg(index, old, new);
 453 }
 454
 455 /**
 456  * sbq_wait_ptr() - Get the next wait queue to use for a &struct
 457  * sbitmap_queue.
 458  * @sbq: Bitmap queue to wait on.
 459  * @wait_index: A counter per "user" of @sbq.
 460  */
 461 static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
 462                                                   atomic_t *wait_index)
 463 {
 464         struct sbq_wait_state *ws;
 465
 466         ws = &sbq->ws[atomic_read(wait_index)];
 467         sbq_index_atomic_inc(wait_index);
 468         return ws;
 469 }
 470
 471 /**
 472  * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
 473  * sbitmap_queue.
 474  * @sbq: Bitmap queue to wake up.
 475  */
 476 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
 477
 478 /**
 479  * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
 480  * seq_file.
 481  * @sbq: Bitmap queue to show.
 482  * @m: struct seq_file to write to.
 483  *
 484  * This is intended for debugging. The format may change at any time.
 485  */
 486 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m);
 487
 488 #endif /* __LINUX_SCALE_BITMAP_H */