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 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 */