lib/sbitmap.c

   1 /*
   2  * Copyright (C) 2016 Facebook
   3  * Copyright (C) 2013-2014 Jens Axboe
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public
   7  * License v2 as published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <linux/sched.h>
  19 #include <linux/random.h>
  20 #include <linux/sbitmap.h>
  21 #include <linux/seq_file.h>
  22
  23 int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
  24                       gfp_t flags, int node)
  25 {
  26         unsigned int bits_per_word;
  27         unsigned int i;
  28
  29         if (shift < 0) {
  30                 shift = ilog2(BITS_PER_LONG);
  31                 /*
  32                  * If the bitmap is small, shrink the number of bits per word so
  33                  * we spread over a few cachelines, at least. If less than 4
  34                  * bits, just forget about it, it's not going to work optimally
  35                  * anyway.
  36                  */
  37                 if (depth >= 4) {
  38                         while ((4U << shift) > depth)
  39                                 shift--;
  40                 }
  41         }
  42         bits_per_word = 1U << shift;
  43         if (bits_per_word > BITS_PER_LONG)
  44                 return -EINVAL;
  45
  46         sb->shift = shift;
  47         sb->depth = depth;
  48         sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  49
  50         if (depth == 0) {
  51                 sb->map = NULL;
  52                 return 0;
  53         }
  54
  55         sb->map = kcalloc_node(sb->map_nr, sizeof(*sb->map), flags, node);
  56         if (!sb->map)
  57                 return -ENOMEM;
  58
  59         for (i = 0; i < sb->map_nr; i++) {
  60                 sb->map[i].depth = min(depth, bits_per_word);
  61                 depth -= sb->map[i].depth;
  62         }
  63         return 0;
  64 }
  65 EXPORT_SYMBOL_GPL(sbitmap_init_node);
  66
  67 void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
  68 {
  69         unsigned int bits_per_word = 1U << sb->shift;
  70         unsigned int i;
  71
  72         sb->depth = depth;
  73         sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
  74
  75         for (i = 0; i < sb->map_nr; i++) {
  76                 sb->map[i].depth = min(depth, bits_per_word);
  77                 depth -= sb->map[i].depth;
  78         }
  79 }
  80 EXPORT_SYMBOL_GPL(sbitmap_resize);
  81
  82 static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
  83                               unsigned int hint, bool wrap)
  84 {
  85         unsigned int orig_hint = hint;
  86         int nr;
  87
  88         while (1) {
  89                 nr = find_next_zero_bit(word, depth, hint);
  90                 if (unlikely(nr >= depth)) {
  91                         /*
  92                          * We started with an offset, and we didn't reset the
  93                          * offset to 0 in a failure case, so start from 0 to
  94                          * exhaust the map.
  95                          */
  96                         if (orig_hint && hint && wrap) {
  97                                 hint = orig_hint = 0;
  98                                 continue;
  99                         }
 100                         return -1;
 101                 }
 102
 103                 if (!test_and_set_bit_lock(nr, word))
 104                         break;
 105
 106                 hint = nr + 1;
 107                 if (hint >= depth - 1)
 108                         hint = 0;
 109         }
 110
 111         return nr;
 112 }
 113
 114 int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
 115 {
 116         unsigned int i, index;
 117         int nr = -1;
 118
 119         index = SB_NR_TO_INDEX(sb, alloc_hint);
 120
 121         for (i = 0; i < sb->map_nr; i++) {
 122                 nr = __sbitmap_get_word(&sb->map[index].word,
 123                                         sb->map[index].depth,
 124                                         SB_NR_TO_BIT(sb, alloc_hint),
 125                                         !round_robin);
 126                 if (nr != -1) {
 127                         nr += index << sb->shift;
 128                         break;
 129                 }
 130
 131                 /* Jump to next index. */
 132                 index++;
 133                 alloc_hint = index << sb->shift;
 134
 135                 if (index >= sb->map_nr) {
 136                         index = 0;
 137                         alloc_hint = 0;
 138                 }
 139         }
 140
 141         return nr;
 142 }
 143 EXPORT_SYMBOL_GPL(sbitmap_get);
 144
 145 int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
 146                         unsigned long shallow_depth)
 147 {
 148         unsigned int i, index;
 149         int nr = -1;
 150
 151         index = SB_NR_TO_INDEX(sb, alloc_hint);
 152
 153         for (i = 0; i < sb->map_nr; i++) {
 154                 nr = __sbitmap_get_word(&sb->map[index].word,
 155                                         min(sb->map[index].depth, shallow_depth),
 156                                         SB_NR_TO_BIT(sb, alloc_hint), true);
 157                 if (nr != -1) {
 158                         nr += index << sb->shift;
 159                         break;
 160                 }
 161
 162                 /* Jump to next index. */
 163                 index++;
 164                 alloc_hint = index << sb->shift;
 165
 166                 if (index >= sb->map_nr) {
 167                         index = 0;
 168                         alloc_hint = 0;
 169                 }
 170         }
 171
 172         return nr;
 173 }
 174 EXPORT_SYMBOL_GPL(sbitmap_get_shallow);
 175
 176 bool sbitmap_any_bit_set(const struct sbitmap *sb)
 177 {
 178         unsigned int i;
 179
 180         for (i = 0; i < sb->map_nr; i++) {
 181                 if (sb->map[i].word)
 182                         return true;
 183         }
 184         return false;
 185 }
 186 EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
 187
 188 bool sbitmap_any_bit_clear(const struct sbitmap *sb)
 189 {
 190         unsigned int i;
 191
 192         for (i = 0; i < sb->map_nr; i++) {
 193                 const struct sbitmap_word *word = &sb->map[i];
 194                 unsigned long ret;
 195
 196                 ret = find_first_zero_bit(&word->word, word->depth);
 197                 if (ret < word->depth)
 198                         return true;
 199         }
 200         return false;
 201 }
 202 EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
 203
 204 unsigned int sbitmap_weight(const struct sbitmap *sb)
 205 {
 206         unsigned int i, weight = 0;
 207
 208         for (i = 0; i < sb->map_nr; i++) {
 209                 const struct sbitmap_word *word = &sb->map[i];
 210
 211                 weight += bitmap_weight(&word->word, word->depth);
 212         }
 213         return weight;
 214 }
 215 EXPORT_SYMBOL_GPL(sbitmap_weight);
 216
 217 void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
 218 {
 219         seq_printf(m, "depth=%u\n", sb->depth);
 220         seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
 221         seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
 222         seq_printf(m, "map_nr=%u\n", sb->map_nr);
 223 }
 224 EXPORT_SYMBOL_GPL(sbitmap_show);
 225
 226 static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
 227 {
 228         if ((offset & 0xf) == 0) {
 229                 if (offset != 0)
 230                         seq_putc(m, '\n');
 231                 seq_printf(m, "%08x:", offset);
 232         }
 233         if ((offset & 0x1) == 0)
 234                 seq_putc(m, ' ');
 235         seq_printf(m, "%02x", byte);
 236 }
 237
 238 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 239 {
 240         u8 byte = 0;
 241         unsigned int byte_bits = 0;
 242         unsigned int offset = 0;
 243         int i;
 244
 245         for (i = 0; i < sb->map_nr; i++) {
 246                 unsigned long word = READ_ONCE(sb->map[i].word);
 247                 unsigned int word_bits = READ_ONCE(sb->map[i].depth);
 248
 249                 while (word_bits > 0) {
 250                         unsigned int bits = min(8 - byte_bits, word_bits);
 251
 252                         byte |= (word & (BIT(bits) - 1)) << byte_bits;
 253                         byte_bits += bits;
 254                         if (byte_bits == 8) {
 255                                 emit_byte(m, offset, byte);
 256                                 byte = 0;
 257                                 byte_bits = 0;
 258                                 offset++;
 259                         }
 260                         word >>= bits;
 261                         word_bits -= bits;
 262                 }
 263         }
 264         if (byte_bits) {
 265                 emit_byte(m, offset, byte);
 266                 offset++;
 267         }
 268         if (offset)
 269                 seq_putc(m, '\n');
 270 }
 271 EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
 272
 273 static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
 274                                         unsigned int depth)
 275 {
 276         unsigned int wake_batch;
 277         unsigned int shallow_depth;
 278
 279         /*
 280          * For each batch, we wake up one queue. We need to make sure that our
 281          * batch size is small enough that the full depth of the bitmap,
 282          * potentially limited by a shallow depth, is enough to wake up all of
 283          * the queues.
 284          *
 285          * Each full word of the bitmap has bits_per_word bits, and there might
 286          * be a partial word. There are depth / bits_per_word full words and
 287          * depth % bits_per_word bits left over. In bitwise arithmetic:
 288          *
 289          * bits_per_word = 1 << shift
 290          * depth / bits_per_word = depth >> shift
 291          * depth % bits_per_word = depth & ((1 << shift) - 1)
 292          *
 293          * Each word can be limited to sbq->min_shallow_depth bits.
 294          */
 295         shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
 296         depth = ((depth >> sbq->sb.shift) * shallow_depth +
 297                  min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
 298         wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
 299                              SBQ_WAKE_BATCH);
 300
 301         return wake_batch;
 302 }
 303
 304 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 305                             int shift, bool round_robin, gfp_t flags, int node)
 306 {
 307         int ret;
 308         int i;
 309
 310         ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
 311         if (ret)
 312                 return ret;
 313
 314         sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
 315         if (!sbq->alloc_hint) {
 316                 sbitmap_free(&sbq->sb);
 317                 return -ENOMEM;
 318         }
 319
 320         if (depth && !round_robin) {
 321                 for_each_possible_cpu(i)
 322                         *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
 323         }
 324
 325         sbq->min_shallow_depth = UINT_MAX;
 326         sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
 327         atomic_set(&sbq->wake_index, 0);
 328
 329         sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
 330         if (!sbq->ws) {
 331                 free_percpu(sbq->alloc_hint);
 332                 sbitmap_free(&sbq->sb);
 333                 return -ENOMEM;
 334         }
 335
 336         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 337                 init_waitqueue_head(&sbq->ws[i].wait);
 338                 atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
 339         }
 340
 341         sbq->round_robin = round_robin;
 342         return 0;
 343 }
 344 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 345
 346 static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
 347                                             unsigned int depth)
 348 {
 349         unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
 350         int i;
 351
 352         if (sbq->wake_batch != wake_batch) {
 353                 WRITE_ONCE(sbq->wake_batch, wake_batch);
 354                 /*
 355                  * Pairs with the memory barrier in sbitmap_queue_wake_up()
 356                  * to ensure that the batch size is updated before the wait
 357                  * counts.
 358                  */
 359                 smp_mb__before_atomic();
 360                 for (i = 0; i < SBQ_WAIT_QUEUES; i++)
 361                         atomic_set(&sbq->ws[i].wait_cnt, 1);
 362         }
 363 }
 364
 365 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 366 {
 367         sbitmap_queue_update_wake_batch(sbq, depth);
 368         sbitmap_resize(&sbq->sb, depth);
 369 }
 370 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
 371
 372 int __sbitmap_queue_get(struct sbitmap_queue *sbq)
 373 {
 374         unsigned int hint, depth;
 375         int nr;
 376
 377         hint = this_cpu_read(*sbq->alloc_hint);
 378         depth = READ_ONCE(sbq->sb.depth);
 379         if (unlikely(hint >= depth)) {
 380                 hint = depth ? prandom_u32() % depth : 0;
 381                 this_cpu_write(*sbq->alloc_hint, hint);
 382         }
 383         nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
 384
 385         if (nr == -1) {
 386                 /* If the map is full, a hint won't do us much good. */
 387                 this_cpu_write(*sbq->alloc_hint, 0);
 388         } else if (nr == hint || unlikely(sbq->round_robin)) {
 389                 /* Only update the hint if we used it. */
 390                 hint = nr + 1;
 391                 if (hint >= depth - 1)
 392                         hint = 0;
 393                 this_cpu_write(*sbq->alloc_hint, hint);
 394         }
 395
 396         return nr;
 397 }
 398 EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
 399
 400 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
 401                                 unsigned int shallow_depth)
 402 {
 403         unsigned int hint, depth;
 404         int nr;
 405
 406         WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);
 407
 408         hint = this_cpu_read(*sbq->alloc_hint);
 409         depth = READ_ONCE(sbq->sb.depth);
 410         if (unlikely(hint >= depth)) {
 411                 hint = depth ? prandom_u32() % depth : 0;
 412                 this_cpu_write(*sbq->alloc_hint, hint);
 413         }
 414         nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
 415
 416         if (nr == -1) {
 417                 /* If the map is full, a hint won't do us much good. */
 418                 this_cpu_write(*sbq->alloc_hint, 0);
 419         } else if (nr == hint || unlikely(sbq->round_robin)) {
 420                 /* Only update the hint if we used it. */
 421                 hint = nr + 1;
 422                 if (hint >= depth - 1)
 423                         hint = 0;
 424                 this_cpu_write(*sbq->alloc_hint, hint);
 425         }
 426
 427         return nr;
 428 }
 429 EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);
 430
 431 void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
 432                                      unsigned int min_shallow_depth)
 433 {
 434         sbq->min_shallow_depth = min_shallow_depth;
 435         sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
 436 }
 437 EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
 438
 439 static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
 440 {
 441         int i, wake_index;
 442
 443         wake_index = atomic_read(&sbq->wake_index);
 444         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 445                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 446
 447                 if (waitqueue_active(&ws->wait)) {
 448                         int o = atomic_read(&sbq->wake_index);
 449
 450                         if (wake_index != o)
 451                                 atomic_cmpxchg(&sbq->wake_index, o, wake_index);
 452                         return ws;
 453                 }
 454
 455                 wake_index = sbq_index_inc(wake_index);
 456         }
 457
 458         return NULL;
 459 }
 460
 461 static bool __sbq_wake_up(struct sbitmap_queue *sbq)
 462 {
 463         struct sbq_wait_state *ws;
 464         unsigned int wake_batch;
 465         int wait_cnt;
 466
 467         ws = sbq_wake_ptr(sbq);
 468         if (!ws)
 469                 return false;
 470
 471         wait_cnt = atomic_dec_return(&ws->wait_cnt);
 472         if (wait_cnt <= 0) {
 473                 int ret;
 474
 475                 wake_batch = READ_ONCE(sbq->wake_batch);
 476
 477                 /*
 478                  * Pairs with the memory barrier in sbitmap_queue_resize() to
 479                  * ensure that we see the batch size update before the wait
 480                  * count is reset.
 481                  */
 482                 smp_mb__before_atomic();
 483
 484                 /*
 485                  * For concurrent callers of this, the one that failed the
 486                  * atomic_cmpxhcg() race should call this function again
 487                  * to wakeup a new batch on a different 'ws'.
 488                  */
 489                 ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
 490                 if (ret == wait_cnt) {
 491                         sbq_index_atomic_inc(&sbq->wake_index);
 492                         wake_up_nr(&ws->wait, wake_batch);
 493                         return false;
 494                 }
 495
 496                 return true;
 497         }
 498
 499         return false;
 500 }
 501
 502 void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
 503 {
 504         while (__sbq_wake_up(sbq))
 505                 ;
 506 }
 507 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
 508
 509 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 510                          unsigned int cpu)
 511 {
 512         sbitmap_clear_bit_unlock(&sbq->sb, nr);
 513         /*
 514          * Pairs with the memory barrier in set_current_state() to ensure the
 515          * proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
 516          * and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
 517          * waiter. See the comment on waitqueue_active().
 518          */
 519         smp_mb__after_atomic();
 520         sbitmap_queue_wake_up(sbq);
 521
 522         if (likely(!sbq->round_robin && nr < sbq->sb.depth))
 523                 *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
 524 }
 525 EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
 526
 527 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 528 {
 529         int i, wake_index;
 530
 531         /*
 532          * Pairs with the memory barrier in set_current_state() like in
 533          * sbitmap_queue_wake_up().
 534          */
 535         smp_mb();
 536         wake_index = atomic_read(&sbq->wake_index);
 537         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 538                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 539
 540                 if (waitqueue_active(&ws->wait))
 541                         wake_up(&ws->wait);
 542
 543                 wake_index = sbq_index_inc(wake_index);
 544         }
 545 }
 546 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
 547
 548 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 549 {
 550         bool first;
 551         int i;
 552
 553         sbitmap_show(&sbq->sb, m);
 554
 555         seq_puts(m, "alloc_hint={");
 556         first = true;
 557         for_each_possible_cpu(i) {
 558                 if (!first)
 559                         seq_puts(m, ", ");
 560                 first = false;
 561                 seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
 562         }
 563         seq_puts(m, "}\n");
 564
 565         seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
 566         seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
 567
 568         seq_puts(m, "ws={\n");
 569         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 570                 struct sbq_wait_state *ws = &sbq->ws[i];
 571
 572                 seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
 573                            atomic_read(&ws->wait_cnt),
 574                            waitqueue_active(&ws->wait) ? "active" : "inactive");
 575         }
 576         seq_puts(m, "}\n");
 577
 578         seq_printf(m, "round_robin=%d\n", sbq->round_robin);
 579         seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
 580 }
 581 EXPORT_SYMBOL_GPL(sbitmap_queue_show);