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_any_bit_set() - Check for a set bit in a &struct sbitmap.
 180  * @sb: Bitmap to check.
 181  *
 182  * Return: true if any bit in the bitmap is set, false otherwise.
 183  */
 184 bool sbitmap_any_bit_set(const struct sbitmap *sb);
 185
 186 /**
 187  * sbitmap_any_bit_clear() - Check for an unset bit in a &struct
 188  * sbitmap.
 189  * @sb: Bitmap to check.
 190  *
 191  * Return: true if any bit in the bitmap is clear, false otherwise.
 192  */
 193 bool sbitmap_any_bit_clear(const struct sbitmap *sb);
 194
 195 typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
 196
 197 /**
 198  * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
 199  * @sb: Bitmap to iterate over.
 200  * @fn: Callback. Should return true to continue or false to break early.
 201  * @data: Pointer to pass to callback.
 202  *
 203  * This is inline even though it's non-trivial so that the function calls to the
 204  * callback will hopefully get optimized away.
 205  */
 206 static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
 207                                         void *data)
 208 {
 209         unsigned int i;
 210
 211         for (i = 0; i < sb->map_nr; i++) {
 212                 struct sbitmap_word *word = &sb->map[i];
 213                 unsigned int off, nr;
 214
 215                 if (!word->word)
 216                         continue;
 217
 218                 nr = 0;
 219                 off = i << sb->shift;
 220                 while (1) {
 221                         nr = find_next_bit(&word->word, word->depth, nr);
 222                         if (nr >= word->depth)
 223                                 break;
 224
 225                         if (!fn(sb, off + nr, data))
 226                                 return;
 227
 228                         nr++;
 229                 }
 230         }
 231 }
 232
 233 #define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
 234 #define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
 235
 236 static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
 237                                             unsigned int bitnr)
 238 {
 239         return &sb->map[SB_NR_TO_INDEX(sb, bitnr)].word;
 240 }
 241
 242 /* Helpers equivalent to the operations in asm/bitops.h and linux/bitmap.h */
 243
 244 static inline void sbitmap_set_bit(struct sbitmap *sb, unsigned int bitnr)
 245 {
 246         set_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 247 }
 248
 249 static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
 250 {
 251         clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 252 }
 253
 254 static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
 255 {
 256         return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
 257 }
 258
 259 unsigned int sbitmap_weight(const struct sbitmap *sb);
 260
 261 /**
 262  * sbitmap_queue_init_node() - Initialize a &struct sbitmap_queue on a specific
 263  * memory node.
 264  * @sbq: Bitmap queue to initialize.
 265  * @depth: See sbitmap_init_node().
 266  * @shift: See sbitmap_init_node().
 267  * @round_robin: See sbitmap_get().
 268  * @flags: Allocation flags.
 269  * @node: Memory node to allocate on.
 270  *
 271  * Return: Zero on success or negative errno on failure.
 272  */
 273 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 274                             int shift, bool round_robin, gfp_t flags, int node);
 275
 276 /**
 277  * sbitmap_queue_free() - Free memory used by a &struct sbitmap_queue.
 278  *
 279  * @sbq: Bitmap queue to free.
 280  */
 281 static inline void sbitmap_queue_free(struct sbitmap_queue *sbq)
 282 {
 283         kfree(sbq->ws);
 284         free_percpu(sbq->alloc_hint);
 285         sbitmap_free(&sbq->sb);
 286 }
 287
 288 /**
 289  * sbitmap_queue_resize() - Resize a &struct sbitmap_queue.
 290  * @sbq: Bitmap queue to resize.
 291  * @depth: New number of bits to resize to.
 292  *
 293  * Like sbitmap_resize(), this doesn't reallocate anything. It has to do
 294  * some extra work on the &struct sbitmap_queue, so it's not safe to just
 295  * resize the underlying &struct sbitmap.
 296  */
 297 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth);
 298
 299 /**
 300  * __sbitmap_queue_get() - Try to allocate a free bit from a &struct
 301  * sbitmap_queue with preemption already disabled.
 302  * @sbq: Bitmap queue to allocate from.
 303  *
 304  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 305  */
 306 int __sbitmap_queue_get(struct sbitmap_queue *sbq);
 307
 308 /**
 309  * sbitmap_queue_get() - Try to allocate a free bit from a &struct
 310  * sbitmap_queue.
 311  * @sbq: Bitmap queue to allocate from.
 312  * @cpu: Output parameter; will contain the CPU we ran on (e.g., to be passed to
 313  *       sbitmap_queue_clear()).
 314  *
 315  * Return: Non-negative allocated bit number if successful, -1 otherwise.
 316  */
 317 static inline int sbitmap_queue_get(struct sbitmap_queue *sbq,
 318                                     unsigned int *cpu)
 319 {
 320         int nr;
 321
 322         *cpu = get_cpu();
 323         nr = __sbitmap_queue_get(sbq);
 324         put_cpu();
 325         return nr;
 326 }
 327
 328 /**
 329  * sbitmap_queue_clear() - Free an allocated bit and wake up waiters on a
 330  * &struct sbitmap_queue.
 331  * @sbq: Bitmap to free from.
 332  * @nr: Bit number to free.
 333  * @cpu: CPU the bit was allocated on.
 334  */
 335 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 336                          unsigned int cpu);
 337
 338 static inline int sbq_index_inc(int index)
 339 {
 340         return (index + 1) & (SBQ_WAIT_QUEUES - 1);
 341 }
 342
 343 static inline void sbq_index_atomic_inc(atomic_t *index)
 344 {
 345         int old = atomic_read(index);
 346         int new = sbq_index_inc(old);
 347         atomic_cmpxchg(index, old, new);
 348 }
 349
 350 /**
 351  * sbq_wait_ptr() - Get the next wait queue to use for a &struct
 352  * sbitmap_queue.
 353  * @sbq: Bitmap queue to wait on.
 354  * @wait_index: A counter per "user" of @sbq.
 355  */
 356 static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
 357                                                   atomic_t *wait_index)
 358 {
 359         struct sbq_wait_state *ws;
 360
 361         ws = &sbq->ws[atomic_read(wait_index)];
 362         sbq_index_atomic_inc(wait_index);
 363         return ws;
 364 }
 365
 366 /**
 367  * sbitmap_queue_wake_all() - Wake up everything waiting on a &struct
 368  * sbitmap_queue.
 369  * @sbq: Bitmap queue to wake up.
 370  */
 371 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
 372
 373 #endif /* __LINUX_SCALE_BITMAP_H */