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 = kzalloc_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(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(unsigned int depth)
 274 {
 275         unsigned int wake_batch;
 276
 277         /*
 278          * For each batch, we wake up one queue. We need to make sure that our
 279          * batch size is small enough that the full depth of the bitmap is
 280          * enough to wake up all of the queues.
 281          */
 282         wake_batch = SBQ_WAKE_BATCH;
 283         if (wake_batch > depth / SBQ_WAIT_QUEUES)
 284                 wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
 285
 286         return wake_batch;
 287 }
 288
 289 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 290                             int shift, bool round_robin, gfp_t flags, int node)
 291 {
 292         int ret;
 293         int i;
 294
 295         ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
 296         if (ret)
 297                 return ret;
 298
 299         sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
 300         if (!sbq->alloc_hint) {
 301                 sbitmap_free(&sbq->sb);
 302                 return -ENOMEM;
 303         }
 304
 305         if (depth && !round_robin) {
 306                 for_each_possible_cpu(i)
 307                         *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
 308         }
 309
 310         sbq->wake_batch = sbq_calc_wake_batch(depth);
 311         atomic_set(&sbq->wake_index, 0);
 312
 313         sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
 314         if (!sbq->ws) {
 315                 free_percpu(sbq->alloc_hint);
 316                 sbitmap_free(&sbq->sb);
 317                 return -ENOMEM;
 318         }
 319
 320         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 321                 init_waitqueue_head(&sbq->ws[i].wait);
 322                 atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
 323         }
 324
 325         sbq->round_robin = round_robin;
 326         return 0;
 327 }
 328 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 329
 330 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 331 {
 332         unsigned int wake_batch = sbq_calc_wake_batch(depth);
 333         int i;
 334
 335         if (sbq->wake_batch != wake_batch) {
 336                 WRITE_ONCE(sbq->wake_batch, wake_batch);
 337                 /*
 338                  * Pairs with the memory barrier in sbq_wake_up() to ensure that
 339                  * the batch size is updated before the wait counts.
 340                  */
 341                 smp_mb__before_atomic();
 342                 for (i = 0; i < SBQ_WAIT_QUEUES; i++)
 343                         atomic_set(&sbq->ws[i].wait_cnt, 1);
 344         }
 345         sbitmap_resize(&sbq->sb, depth);
 346 }
 347 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
 348
 349 int __sbitmap_queue_get(struct sbitmap_queue *sbq)
 350 {
 351         unsigned int hint, depth;
 352         int nr;
 353
 354         hint = this_cpu_read(*sbq->alloc_hint);
 355         depth = READ_ONCE(sbq->sb.depth);
 356         if (unlikely(hint >= depth)) {
 357                 hint = depth ? prandom_u32() % depth : 0;
 358                 this_cpu_write(*sbq->alloc_hint, hint);
 359         }
 360         nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
 361
 362         if (nr == -1) {
 363                 /* If the map is full, a hint won't do us much good. */
 364                 this_cpu_write(*sbq->alloc_hint, 0);
 365         } else if (nr == hint || unlikely(sbq->round_robin)) {
 366                 /* Only update the hint if we used it. */
 367                 hint = nr + 1;
 368                 if (hint >= depth - 1)
 369                         hint = 0;
 370                 this_cpu_write(*sbq->alloc_hint, hint);
 371         }
 372
 373         return nr;
 374 }
 375 EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
 376
 377 int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
 378                                 unsigned int shallow_depth)
 379 {
 380         unsigned int hint, depth;
 381         int nr;
 382
 383         hint = this_cpu_read(*sbq->alloc_hint);
 384         depth = READ_ONCE(sbq->sb.depth);
 385         if (unlikely(hint >= depth)) {
 386                 hint = depth ? prandom_u32() % depth : 0;
 387                 this_cpu_write(*sbq->alloc_hint, hint);
 388         }
 389         nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);
 390
 391         if (nr == -1) {
 392                 /* If the map is full, a hint won't do us much good. */
 393                 this_cpu_write(*sbq->alloc_hint, 0);
 394         } else if (nr == hint || unlikely(sbq->round_robin)) {
 395                 /* Only update the hint if we used it. */
 396                 hint = nr + 1;
 397                 if (hint >= depth - 1)
 398                         hint = 0;
 399                 this_cpu_write(*sbq->alloc_hint, hint);
 400         }
 401
 402         return nr;
 403 }
 404 EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);
 405
 406 static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
 407 {
 408         int i, wake_index;
 409
 410         wake_index = atomic_read(&sbq->wake_index);
 411         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 412                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 413
 414                 if (waitqueue_active(&ws->wait)) {
 415                         int o = atomic_read(&sbq->wake_index);
 416
 417                         if (wake_index != o)
 418                                 atomic_cmpxchg(&sbq->wake_index, o, wake_index);
 419                         return ws;
 420                 }
 421
 422                 wake_index = sbq_index_inc(wake_index);
 423         }
 424
 425         return NULL;
 426 }
 427
 428 static void sbq_wake_up(struct sbitmap_queue *sbq)
 429 {
 430         struct sbq_wait_state *ws;
 431         unsigned int wake_batch;
 432         int wait_cnt;
 433
 434         /*
 435          * Pairs with the memory barrier in set_current_state() to ensure the
 436          * proper ordering of clear_bit()/waitqueue_active() in the waker and
 437          * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
 438          * the comment on waitqueue_active(). This is __after_atomic because we
 439          * just did clear_bit() in the caller.
 440          */
 441         smp_mb__after_atomic();
 442
 443         ws = sbq_wake_ptr(sbq);
 444         if (!ws)
 445                 return;
 446
 447         wait_cnt = atomic_dec_return(&ws->wait_cnt);
 448         if (wait_cnt <= 0) {
 449                 wake_batch = READ_ONCE(sbq->wake_batch);
 450                 /*
 451                  * Pairs with the memory barrier in sbitmap_queue_resize() to
 452                  * ensure that we see the batch size update before the wait
 453                  * count is reset.
 454                  */
 455                 smp_mb__before_atomic();
 456                 /*
 457                  * If there are concurrent callers to sbq_wake_up(), the last
 458                  * one to decrement the wait count below zero will bump it back
 459                  * up. If there is a concurrent resize, the count reset will
 460                  * either cause the cmpxchg to fail or overwrite after the
 461                  * cmpxchg.
 462                  */
 463                 atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wait_cnt + wake_batch);
 464                 sbq_index_atomic_inc(&sbq->wake_index);
 465                 wake_up(&ws->wait);
 466         }
 467 }
 468
 469 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 470                          unsigned int cpu)
 471 {
 472         sbitmap_clear_bit(&sbq->sb, nr);
 473         sbq_wake_up(sbq);
 474         if (likely(!sbq->round_robin && nr < sbq->sb.depth))
 475                 *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
 476 }
 477 EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
 478
 479 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 480 {
 481         int i, wake_index;
 482
 483         /*
 484          * Pairs with the memory barrier in set_current_state() like in
 485          * sbq_wake_up().
 486          */
 487         smp_mb();
 488         wake_index = atomic_read(&sbq->wake_index);
 489         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 490                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 491
 492                 if (waitqueue_active(&ws->wait))
 493                         wake_up(&ws->wait);
 494
 495                 wake_index = sbq_index_inc(wake_index);
 496         }
 497 }
 498 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
 499
 500 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 501 {
 502         bool first;
 503         int i;
 504
 505         sbitmap_show(&sbq->sb, m);
 506
 507         seq_puts(m, "alloc_hint={");
 508         first = true;
 509         for_each_possible_cpu(i) {
 510                 if (!first)
 511                         seq_puts(m, ", ");
 512                 first = false;
 513                 seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
 514         }
 515         seq_puts(m, "}\n");
 516
 517         seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
 518         seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
 519
 520         seq_puts(m, "ws={\n");
 521         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 522                 struct sbq_wait_state *ws = &sbq->ws[i];
 523
 524                 seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
 525                            atomic_read(&ws->wait_cnt),
 526                            waitqueue_active(&ws->wait) ? "active" : "inactive");
 527         }
 528         seq_puts(m, "}\n");
 529
 530         seq_printf(m, "round_robin=%d\n", sbq->round_robin);
 531 }
 532 EXPORT_SYMBOL_GPL(sbitmap_queue_show);