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(struct sbitmap_word *word, unsigned int hint,
  83                               bool wrap)
  84 {
  85         unsigned int orig_hint = hint;
  86         int nr;
  87
  88         while (1) {
  89                 nr = find_next_zero_bit(&word->word, word->depth, hint);
  90                 if (unlikely(nr >= word->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->word))
 104                         break;
 105
 106                 hint = nr + 1;
 107                 if (hint >= word->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],
 123                                         SB_NR_TO_BIT(sb, alloc_hint),
 124                                         !round_robin);
 125                 if (nr != -1) {
 126                         nr += index << sb->shift;
 127                         break;
 128                 }
 129
 130                 /* Jump to next index. */
 131                 index++;
 132                 alloc_hint = index << sb->shift;
 133
 134                 if (index >= sb->map_nr) {
 135                         index = 0;
 136                         alloc_hint = 0;
 137                 }
 138         }
 139
 140         return nr;
 141 }
 142 EXPORT_SYMBOL_GPL(sbitmap_get);
 143
 144 bool sbitmap_any_bit_set(const struct sbitmap *sb)
 145 {
 146         unsigned int i;
 147
 148         for (i = 0; i < sb->map_nr; i++) {
 149                 if (sb->map[i].word)
 150                         return true;
 151         }
 152         return false;
 153 }
 154 EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);
 155
 156 bool sbitmap_any_bit_clear(const struct sbitmap *sb)
 157 {
 158         unsigned int i;
 159
 160         for (i = 0; i < sb->map_nr; i++) {
 161                 const struct sbitmap_word *word = &sb->map[i];
 162                 unsigned long ret;
 163
 164                 ret = find_first_zero_bit(&word->word, word->depth);
 165                 if (ret < word->depth)
 166                         return true;
 167         }
 168         return false;
 169 }
 170 EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
 171
 172 unsigned int sbitmap_weight(const struct sbitmap *sb)
 173 {
 174         unsigned int i, weight = 0;
 175
 176         for (i = 0; i < sb->map_nr; i++) {
 177                 const struct sbitmap_word *word = &sb->map[i];
 178
 179                 weight += bitmap_weight(&word->word, word->depth);
 180         }
 181         return weight;
 182 }
 183 EXPORT_SYMBOL_GPL(sbitmap_weight);
 184
 185 void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
 186 {
 187         seq_printf(m, "depth=%u\n", sb->depth);
 188         seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
 189         seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
 190         seq_printf(m, "map_nr=%u\n", sb->map_nr);
 191 }
 192 EXPORT_SYMBOL_GPL(sbitmap_show);
 193
 194 static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
 195 {
 196         if ((offset & 0xf) == 0) {
 197                 if (offset != 0)
 198                         seq_putc(m, '\n');
 199                 seq_printf(m, "%08x:", offset);
 200         }
 201         if ((offset & 0x1) == 0)
 202                 seq_putc(m, ' ');
 203         seq_printf(m, "%02x", byte);
 204 }
 205
 206 void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 207 {
 208         u8 byte = 0;
 209         unsigned int byte_bits = 0;
 210         unsigned int offset = 0;
 211         int i;
 212
 213         for (i = 0; i < sb->map_nr; i++) {
 214                 unsigned long word = READ_ONCE(sb->map[i].word);
 215                 unsigned int word_bits = READ_ONCE(sb->map[i].depth);
 216
 217                 while (word_bits > 0) {
 218                         unsigned int bits = min(8 - byte_bits, word_bits);
 219
 220                         byte |= (word & (BIT(bits) - 1)) << byte_bits;
 221                         byte_bits += bits;
 222                         if (byte_bits == 8) {
 223                                 emit_byte(m, offset, byte);
 224                                 byte = 0;
 225                                 byte_bits = 0;
 226                                 offset++;
 227                         }
 228                         word >>= bits;
 229                         word_bits -= bits;
 230                 }
 231         }
 232         if (byte_bits) {
 233                 emit_byte(m, offset, byte);
 234                 offset++;
 235         }
 236         if (offset)
 237                 seq_putc(m, '\n');
 238 }
 239 EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
 240
 241 static unsigned int sbq_calc_wake_batch(unsigned int depth)
 242 {
 243         unsigned int wake_batch;
 244
 245         /*
 246          * For each batch, we wake up one queue. We need to make sure that our
 247          * batch size is small enough that the full depth of the bitmap is
 248          * enough to wake up all of the queues.
 249          */
 250         wake_batch = SBQ_WAKE_BATCH;
 251         if (wake_batch > depth / SBQ_WAIT_QUEUES)
 252                 wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
 253
 254         return wake_batch;
 255 }
 256
 257 int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
 258                             int shift, bool round_robin, gfp_t flags, int node)
 259 {
 260         int ret;
 261         int i;
 262
 263         ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
 264         if (ret)
 265                 return ret;
 266
 267         sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
 268         if (!sbq->alloc_hint) {
 269                 sbitmap_free(&sbq->sb);
 270                 return -ENOMEM;
 271         }
 272
 273         if (depth && !round_robin) {
 274                 for_each_possible_cpu(i)
 275                         *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
 276         }
 277
 278         sbq->wake_batch = sbq_calc_wake_batch(depth);
 279         atomic_set(&sbq->wake_index, 0);
 280
 281         sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
 282         if (!sbq->ws) {
 283                 free_percpu(sbq->alloc_hint);
 284                 sbitmap_free(&sbq->sb);
 285                 return -ENOMEM;
 286         }
 287
 288         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 289                 init_waitqueue_head(&sbq->ws[i].wait);
 290                 atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
 291         }
 292
 293         sbq->round_robin = round_robin;
 294         return 0;
 295 }
 296 EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 297
 298 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 299 {
 300         unsigned int wake_batch = sbq_calc_wake_batch(depth);
 301         int i;
 302
 303         if (sbq->wake_batch != wake_batch) {
 304                 WRITE_ONCE(sbq->wake_batch, wake_batch);
 305                 /*
 306                  * Pairs with the memory barrier in sbq_wake_up() to ensure that
 307                  * the batch size is updated before the wait counts.
 308                  */
 309                 smp_mb__before_atomic();
 310                 for (i = 0; i < SBQ_WAIT_QUEUES; i++)
 311                         atomic_set(&sbq->ws[i].wait_cnt, 1);
 312         }
 313         sbitmap_resize(&sbq->sb, depth);
 314 }
 315 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
 316
 317 int __sbitmap_queue_get(struct sbitmap_queue *sbq)
 318 {
 319         unsigned int hint, depth;
 320         int nr;
 321
 322         hint = this_cpu_read(*sbq->alloc_hint);
 323         depth = READ_ONCE(sbq->sb.depth);
 324         if (unlikely(hint >= depth)) {
 325                 hint = depth ? prandom_u32() % depth : 0;
 326                 this_cpu_write(*sbq->alloc_hint, hint);
 327         }
 328         nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);
 329
 330         if (nr == -1) {
 331                 /* If the map is full, a hint won't do us much good. */
 332                 this_cpu_write(*sbq->alloc_hint, 0);
 333         } else if (nr == hint || unlikely(sbq->round_robin)) {
 334                 /* Only update the hint if we used it. */
 335                 hint = nr + 1;
 336                 if (hint >= depth - 1)
 337                         hint = 0;
 338                 this_cpu_write(*sbq->alloc_hint, hint);
 339         }
 340
 341         return nr;
 342 }
 343 EXPORT_SYMBOL_GPL(__sbitmap_queue_get);
 344
 345 static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
 346 {
 347         int i, wake_index;
 348
 349         wake_index = atomic_read(&sbq->wake_index);
 350         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 351                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 352
 353                 if (waitqueue_active(&ws->wait)) {
 354                         int o = atomic_read(&sbq->wake_index);
 355
 356                         if (wake_index != o)
 357                                 atomic_cmpxchg(&sbq->wake_index, o, wake_index);
 358                         return ws;
 359                 }
 360
 361                 wake_index = sbq_index_inc(wake_index);
 362         }
 363
 364         return NULL;
 365 }
 366
 367 static void sbq_wake_up(struct sbitmap_queue *sbq)
 368 {
 369         struct sbq_wait_state *ws;
 370         unsigned int wake_batch;
 371         int wait_cnt;
 372
 373         /*
 374          * Pairs with the memory barrier in set_current_state() to ensure the
 375          * proper ordering of clear_bit()/waitqueue_active() in the waker and
 376          * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
 377          * the comment on waitqueue_active(). This is __after_atomic because we
 378          * just did clear_bit() in the caller.
 379          */
 380         smp_mb__after_atomic();
 381
 382         ws = sbq_wake_ptr(sbq);
 383         if (!ws)
 384                 return;
 385
 386         wait_cnt = atomic_dec_return(&ws->wait_cnt);
 387         if (wait_cnt <= 0) {
 388                 wake_batch = READ_ONCE(sbq->wake_batch);
 389                 /*
 390                  * Pairs with the memory barrier in sbitmap_queue_resize() to
 391                  * ensure that we see the batch size update before the wait
 392                  * count is reset.
 393                  */
 394                 smp_mb__before_atomic();
 395                 /*
 396                  * If there are concurrent callers to sbq_wake_up(), the last
 397                  * one to decrement the wait count below zero will bump it back
 398                  * up. If there is a concurrent resize, the count reset will
 399                  * either cause the cmpxchg to fail or overwrite after the
 400                  * cmpxchg.
 401                  */
 402                 atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wait_cnt + wake_batch);
 403                 sbq_index_atomic_inc(&sbq->wake_index);
 404                 wake_up(&ws->wait);
 405         }
 406 }
 407
 408 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
 409                          unsigned int cpu)
 410 {
 411         sbitmap_clear_bit(&sbq->sb, nr);
 412         sbq_wake_up(sbq);
 413         if (likely(!sbq->round_robin && nr < sbq->sb.depth))
 414                 *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
 415 }
 416 EXPORT_SYMBOL_GPL(sbitmap_queue_clear);
 417
 418 void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 419 {
 420         int i, wake_index;
 421
 422         /*
 423          * Pairs with the memory barrier in set_current_state() like in
 424          * sbq_wake_up().
 425          */
 426         smp_mb();
 427         wake_index = atomic_read(&sbq->wake_index);
 428         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 429                 struct sbq_wait_state *ws = &sbq->ws[wake_index];
 430
 431                 if (waitqueue_active(&ws->wait))
 432                         wake_up(&ws->wait);
 433
 434                 wake_index = sbq_index_inc(wake_index);
 435         }
 436 }
 437 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
 438
 439 void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
 440 {
 441         bool first;
 442         int i;
 443
 444         sbitmap_show(&sbq->sb, m);
 445
 446         seq_puts(m, "alloc_hint={");
 447         first = true;
 448         for_each_possible_cpu(i) {
 449                 if (!first)
 450                         seq_puts(m, ", ");
 451                 first = false;
 452                 seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
 453         }
 454         seq_puts(m, "}\n");
 455
 456         seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
 457         seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
 458
 459         seq_puts(m, "ws={\n");
 460         for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
 461                 struct sbq_wait_state *ws = &sbq->ws[i];
 462
 463                 seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
 464                            atomic_read(&ws->wait_cnt),
 465                            waitqueue_active(&ws->wait) ? "active" : "inactive");
 466         }
 467         seq_puts(m, "}\n");
 468
 469         seq_printf(m, "round_robin=%d\n", sbq->round_robin);
 470 }
 471 EXPORT_SYMBOL_GPL(sbitmap_queue_show);