drivers/md/dm-cache-policy-mq.c

   1 /*
   2  * Copyright (C) 2012 Red Hat. All rights reserved.
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-cache-policy.h"
   8 #include "dm.h"
   9
  10 #include <linux/hash.h>
  11 #include <linux/module.h>
  12 #include <linux/mutex.h>
  13 #include <linux/slab.h>
  14 #include <linux/vmalloc.h>
  15
  16 #define DM_MSG_PREFIX "cache-policy-mq"
  17
  18 static struct kmem_cache *mq_entry_cache;
  19
  20 /*----------------------------------------------------------------*/
  21
  22 static unsigned next_power(unsigned n, unsigned min)
  23 {
  24         return roundup_pow_of_two(max(n, min));
  25 }
  26
  27 /*----------------------------------------------------------------*/
  28
  29 /*
  30  * Large, sequential ios are probably better left on the origin device since
  31  * spindles tend to have good bandwidth.
  32  *
  33  * The io_tracker tries to spot when the io is in one of these sequential
  34  * modes.
  35  *
  36  * Two thresholds to switch between random and sequential io mode are defaulting
  37  * as follows and can be adjusted via the constructor and message interfaces.
  38  */
  39 #define RANDOM_THRESHOLD_DEFAULT 4
  40 #define SEQUENTIAL_THRESHOLD_DEFAULT 512
  41
  42 enum io_pattern {
  43         PATTERN_SEQUENTIAL,
  44         PATTERN_RANDOM
  45 };
  46
  47 struct io_tracker {
  48         enum io_pattern pattern;
  49
  50         unsigned nr_seq_samples;
  51         unsigned nr_rand_samples;
  52         unsigned thresholds[2];
  53
  54         dm_oblock_t last_end_oblock;
  55 };
  56
  57 static void iot_init(struct io_tracker *t,
  58                      int sequential_threshold, int random_threshold)
  59 {
  60         t->pattern = PATTERN_RANDOM;
  61         t->nr_seq_samples = 0;
  62         t->nr_rand_samples = 0;
  63         t->last_end_oblock = 0;
  64         t->thresholds[PATTERN_RANDOM] = random_threshold;
  65         t->thresholds[PATTERN_SEQUENTIAL] = sequential_threshold;
  66 }
  67
  68 static enum io_pattern iot_pattern(struct io_tracker *t)
  69 {
  70         return t->pattern;
  71 }
  72
  73 static void iot_update_stats(struct io_tracker *t, struct bio *bio)
  74 {
  75         if (bio->bi_iter.bi_sector == from_oblock(t->last_end_oblock) + 1)
  76                 t->nr_seq_samples++;
  77         else {
  78                 /*
  79                  * Just one non-sequential IO is enough to reset the
  80                  * counters.
  81                  */
  82                 if (t->nr_seq_samples) {
  83                         t->nr_seq_samples = 0;
  84                         t->nr_rand_samples = 0;
  85                 }
  86
  87                 t->nr_rand_samples++;
  88         }
  89
  90         t->last_end_oblock = to_oblock(bio_end_sector(bio) - 1);
  91 }
  92
  93 static void iot_check_for_pattern_switch(struct io_tracker *t)
  94 {
  95         switch (t->pattern) {
  96         case PATTERN_SEQUENTIAL:
  97                 if (t->nr_rand_samples >= t->thresholds[PATTERN_RANDOM]) {
  98                         t->pattern = PATTERN_RANDOM;
  99                         t->nr_seq_samples = t->nr_rand_samples = 0;
 100                 }
 101                 break;
 102
 103         case PATTERN_RANDOM:
 104                 if (t->nr_seq_samples >= t->thresholds[PATTERN_SEQUENTIAL]) {
 105                         t->pattern = PATTERN_SEQUENTIAL;
 106                         t->nr_seq_samples = t->nr_rand_samples = 0;
 107                 }
 108                 break;
 109         }
 110 }
 111
 112 static void iot_examine_bio(struct io_tracker *t, struct bio *bio)
 113 {
 114         iot_update_stats(t, bio);
 115         iot_check_for_pattern_switch(t);
 116 }
 117
 118 /*----------------------------------------------------------------*/
 119
 120
 121 /*
 122  * This queue is divided up into different levels.  Allowing us to push
 123  * entries to the back of any of the levels.  Think of it as a partially
 124  * sorted queue.
 125  */
 126 #define NR_QUEUE_LEVELS 16u
 127
 128 struct queue {
 129         struct list_head qs[NR_QUEUE_LEVELS];
 130 };
 131
 132 static void queue_init(struct queue *q)
 133 {
 134         unsigned i;
 135
 136         for (i = 0; i < NR_QUEUE_LEVELS; i++)
 137                 INIT_LIST_HEAD(q->qs + i);
 138 }
 139
 140 /*
 141  * Checks to see if the queue is empty.
 142  * FIXME: reduce cpu usage.
 143  */
 144 static bool queue_empty(struct queue *q)
 145 {
 146         unsigned i;
 147
 148         for (i = 0; i < NR_QUEUE_LEVELS; i++)
 149                 if (!list_empty(q->qs + i))
 150                         return false;
 151
 152         return true;
 153 }
 154
 155 /*
 156  * Insert an entry to the back of the given level.
 157  */
 158 static void queue_push(struct queue *q, unsigned level, struct list_head *elt)
 159 {
 160         list_add_tail(elt, q->qs + level);
 161 }
 162
 163 static void queue_remove(struct list_head *elt)
 164 {
 165         list_del(elt);
 166 }
 167
 168 /*
 169  * Shifts all regions down one level.  This has no effect on the order of
 170  * the queue.
 171  */
 172 static void queue_shift_down(struct queue *q)
 173 {
 174         unsigned level;
 175
 176         for (level = 1; level < NR_QUEUE_LEVELS; level++)
 177                 list_splice_init(q->qs + level, q->qs + level - 1);
 178 }
 179
 180 /*
 181  * Gives us the oldest entry of the lowest popoulated level.  If the first
 182  * level is emptied then we shift down one level.
 183  */
 184 static struct list_head *queue_pop(struct queue *q)
 185 {
 186         unsigned level;
 187         struct list_head *r;
 188
 189         for (level = 0; level < NR_QUEUE_LEVELS; level++)
 190                 if (!list_empty(q->qs + level)) {
 191                         r = q->qs[level].next;
 192                         list_del(r);
 193
 194                         /* have we just emptied the bottom level? */
 195                         if (level == 0 && list_empty(q->qs))
 196                                 queue_shift_down(q);
 197
 198                         return r;
 199                 }
 200
 201         return NULL;
 202 }
 203
 204 static struct list_head *list_pop(struct list_head *lh)
 205 {
 206         struct list_head *r = lh->next;
 207
 208         BUG_ON(!r);
 209         list_del_init(r);
 210
 211         return r;
 212 }
 213
 214 /*----------------------------------------------------------------*/
 215
 216 /*
 217  * Describes a cache entry.  Used in both the cache and the pre_cache.
 218  */
 219 struct entry {
 220         struct hlist_node hlist;
 221         struct list_head list;
 222         dm_oblock_t oblock;
 223
 224         /*
 225          * FIXME: pack these better
 226          */
 227         bool dirty:1;
 228         unsigned hit_count;
 229         unsigned generation;
 230         unsigned tick;
 231 };
 232
 233 /*
 234  * Rather than storing the cblock in an entry, we allocate all entries in
 235  * an array, and infer the cblock from the entry position.
 236  *
 237  * Free entries are linked together into a list.
 238  */
 239 struct entry_pool {
 240         struct entry *entries, *entries_end;
 241         struct list_head free;
 242         unsigned nr_allocated;
 243 };
 244
 245 static int epool_init(struct entry_pool *ep, unsigned nr_entries)
 246 {
 247         unsigned i;
 248
 249         ep->entries = vzalloc(sizeof(struct entry) * nr_entries);
 250         if (!ep->entries)
 251                 return -ENOMEM;
 252
 253         ep->entries_end = ep->entries + nr_entries;
 254
 255         INIT_LIST_HEAD(&ep->free);
 256         for (i = 0; i < nr_entries; i++)
 257                 list_add(&ep->entries[i].list, &ep->free);
 258
 259         ep->nr_allocated = 0;
 260
 261         return 0;
 262 }
 263
 264 static void epool_exit(struct entry_pool *ep)
 265 {
 266         vfree(ep->entries);
 267 }
 268
 269 static struct entry *alloc_entry(struct entry_pool *ep)
 270 {
 271         struct entry *e;
 272
 273         if (list_empty(&ep->free))
 274                 return NULL;
 275
 276         e = list_entry(list_pop(&ep->free), struct entry, list);
 277         INIT_LIST_HEAD(&e->list);
 278         INIT_HLIST_NODE(&e->hlist);
 279         ep->nr_allocated++;
 280
 281         return e;
 282 }
 283
 284 /*
 285  * This assumes the cblock hasn't already been allocated.
 286  */
 287 static struct entry *alloc_particular_entry(struct entry_pool *ep, dm_cblock_t cblock)
 288 {
 289         struct entry *e = ep->entries + from_cblock(cblock);
 290
 291         list_del_init(&e->list);
 292         INIT_HLIST_NODE(&e->hlist);
 293         ep->nr_allocated++;
 294
 295         return e;
 296 }
 297
 298 static void free_entry(struct entry_pool *ep, struct entry *e)
 299 {
 300         BUG_ON(!ep->nr_allocated);
 301         ep->nr_allocated--;
 302         INIT_HLIST_NODE(&e->hlist);
 303         list_add(&e->list, &ep->free);
 304 }
 305
 306 /*
 307  * Returns NULL if the entry is free.
 308  */
 309 static struct entry *epool_find(struct entry_pool *ep, dm_cblock_t cblock)
 310 {
 311         struct entry *e = ep->entries + from_cblock(cblock);
 312         return !hlist_unhashed(&e->hlist) ? e : NULL;
 313 }
 314
 315 static bool epool_empty(struct entry_pool *ep)
 316 {
 317         return list_empty(&ep->free);
 318 }
 319
 320 static bool in_pool(struct entry_pool *ep, struct entry *e)
 321 {
 322         return e >= ep->entries && e < ep->entries_end;
 323 }
 324
 325 static dm_cblock_t infer_cblock(struct entry_pool *ep, struct entry *e)
 326 {
 327         return to_cblock(e - ep->entries);
 328 }
 329
 330 /*----------------------------------------------------------------*/
 331
 332 struct mq_policy {
 333         struct dm_cache_policy policy;
 334
 335         /* protects everything */
 336         struct mutex lock;
 337         dm_cblock_t cache_size;
 338         struct io_tracker tracker;
 339
 340         /*
 341          * Entries come from two pools, one of pre-cache entries, and one
 342          * for the cache proper.
 343          */
 344         struct entry_pool pre_cache_pool;
 345         struct entry_pool cache_pool;
 346
 347         /*
 348          * We maintain three queues of entries.  The cache proper,
 349          * consisting of a clean and dirty queue, contains the currently
 350          * active mappings.  Whereas the pre_cache tracks blocks that
 351          * are being hit frequently and potential candidates for promotion
 352          * to the cache.
 353          */
 354         struct queue pre_cache;
 355         struct queue cache_clean;
 356         struct queue cache_dirty;
 357
 358         /*
 359          * Keeps track of time, incremented by the core.  We use this to
 360          * avoid attributing multiple hits within the same tick.
 361          *
 362          * Access to tick_protected should be done with the spin lock held.
 363          * It's copied to tick at the start of the map function (within the
 364          * mutex).
 365          */
 366         spinlock_t tick_lock;
 367         unsigned tick_protected;
 368         unsigned tick;
 369
 370         /*
 371          * A count of the number of times the map function has been called
 372          * and found an entry in the pre_cache or cache.  Currently used to
 373          * calculate the generation.
 374          */
 375         unsigned hit_count;
 376
 377         /*
 378          * A generation is a longish period that is used to trigger some
 379          * book keeping effects.  eg, decrementing hit counts on entries.
 380          * This is needed to allow the cache to evolve as io patterns
 381          * change.
 382          */
 383         unsigned generation;
 384         unsigned generation_period; /* in lookups (will probably change) */
 385
 386         /*
 387          * Entries in the pre_cache whose hit count passes the promotion
 388          * threshold move to the cache proper.  Working out the correct
 389          * value for the promotion_threshold is crucial to this policy.
 390          */
 391         unsigned promote_threshold;
 392
 393         unsigned discard_promote_adjustment;
 394         unsigned read_promote_adjustment;
 395         unsigned write_promote_adjustment;
 396
 397         /*
 398          * The hash table allows us to quickly find an entry by origin
 399          * block.  Both pre_cache and cache entries are in here.
 400          */
 401         unsigned nr_buckets;
 402         dm_block_t hash_bits;
 403         struct hlist_head *table;
 404 };
 405
 406 #define DEFAULT_DISCARD_PROMOTE_ADJUSTMENT 1
 407 #define DEFAULT_READ_PROMOTE_ADJUSTMENT 4
 408 #define DEFAULT_WRITE_PROMOTE_ADJUSTMENT 8
 409
 410 /*----------------------------------------------------------------*/
 411
 412 /*
 413  * Simple hash table implementation.  Should replace with the standard hash
 414  * table that's making its way upstream.
 415  */
 416 static void hash_insert(struct mq_policy *mq, struct entry *e)
 417 {
 418         unsigned h = hash_64(from_oblock(e->oblock), mq->hash_bits);
 419
 420         hlist_add_head(&e->hlist, mq->table + h);
 421 }
 422
 423 static struct entry *hash_lookup(struct mq_policy *mq, dm_oblock_t oblock)
 424 {
 425         unsigned h = hash_64(from_oblock(oblock), mq->hash_bits);
 426         struct hlist_head *bucket = mq->table + h;
 427         struct entry *e;
 428
 429         hlist_for_each_entry(e, bucket, hlist)
 430                 if (e->oblock == oblock) {
 431                         hlist_del(&e->hlist);
 432                         hlist_add_head(&e->hlist, bucket);
 433                         return e;
 434                 }
 435
 436         return NULL;
 437 }
 438
 439 static void hash_remove(struct entry *e)
 440 {
 441         hlist_del(&e->hlist);
 442 }
 443
 444 /*----------------------------------------------------------------*/
 445
 446 static bool any_free_cblocks(struct mq_policy *mq)
 447 {
 448         return !epool_empty(&mq->cache_pool);
 449 }
 450
 451 static bool any_clean_cblocks(struct mq_policy *mq)
 452 {
 453         return !queue_empty(&mq->cache_clean);
 454 }
 455
 456 /*----------------------------------------------------------------*/
 457
 458 /*
 459  * Now we get to the meat of the policy.  This section deals with deciding
 460  * when to to add entries to the pre_cache and cache, and move between
 461  * them.
 462  */
 463
 464 /*
 465  * The queue level is based on the log2 of the hit count.
 466  */
 467 static unsigned queue_level(struct entry *e)
 468 {
 469         return min((unsigned) ilog2(e->hit_count), NR_QUEUE_LEVELS - 1u);
 470 }
 471
 472 static bool in_cache(struct mq_policy *mq, struct entry *e)
 473 {
 474         return in_pool(&mq->cache_pool, e);
 475 }
 476
 477 /*
 478  * Inserts the entry into the pre_cache or the cache.  Ensures the cache
 479  * block is marked as allocated if necc.  Inserts into the hash table.
 480  * Sets the tick which records when the entry was last moved about.
 481  */
 482 static void push(struct mq_policy *mq, struct entry *e)
 483 {
 484         e->tick = mq->tick;
 485         hash_insert(mq, e);
 486
 487         if (in_cache(mq, e))
 488                 queue_push(e->dirty ? &mq->cache_dirty : &mq->cache_clean,
 489                            queue_level(e), &e->list);
 490         else
 491                 queue_push(&mq->pre_cache, queue_level(e), &e->list);
 492 }
 493
 494 /*
 495  * Removes an entry from pre_cache or cache.  Removes from the hash table.
 496  */
 497 static void del(struct mq_policy *mq, struct entry *e)
 498 {
 499         queue_remove(&e->list);
 500         hash_remove(e);
 501 }
 502
 503 /*
 504  * Like del, except it removes the first entry in the queue (ie. the least
 505  * recently used).
 506  */
 507 static struct entry *pop(struct mq_policy *mq, struct queue *q)
 508 {
 509         struct entry *e;
 510         struct list_head *h = queue_pop(q);
 511
 512         if (!h)
 513                 return NULL;
 514
 515         e = container_of(h, struct entry, list);
 516         hash_remove(e);
 517
 518         return e;
 519 }
 520
 521 /*
 522  * Has this entry already been updated?
 523  */
 524 static bool updated_this_tick(struct mq_policy *mq, struct entry *e)
 525 {
 526         return mq->tick == e->tick;
 527 }
 528
 529 /*
 530  * The promotion threshold is adjusted every generation.  As are the counts
 531  * of the entries.
 532  *
 533  * At the moment the threshold is taken by averaging the hit counts of some
 534  * of the entries in the cache (the first 20 entries across all levels in
 535  * ascending order, giving preference to the clean entries at each level).
 536  *
 537  * We can be much cleverer than this though.  For example, each promotion
 538  * could bump up the threshold helping to prevent churn.  Much more to do
 539  * here.
 540  */
 541
 542 #define MAX_TO_AVERAGE 20
 543
 544 static void check_generation(struct mq_policy *mq)
 545 {
 546         unsigned total = 0, nr = 0, count = 0, level;
 547         struct list_head *head;
 548         struct entry *e;
 549
 550         if ((mq->hit_count >= mq->generation_period) && (epool_empty(&mq->cache_pool))) {
 551                 mq->hit_count = 0;
 552                 mq->generation++;
 553
 554                 for (level = 0; level < NR_QUEUE_LEVELS && count < MAX_TO_AVERAGE; level++) {
 555                         head = mq->cache_clean.qs + level;
 556                         list_for_each_entry(e, head, list) {
 557                                 nr++;
 558                                 total += e->hit_count;
 559
 560                                 if (++count >= MAX_TO_AVERAGE)
 561                                         break;
 562                         }
 563
 564                         head = mq->cache_dirty.qs + level;
 565                         list_for_each_entry(e, head, list) {
 566                                 nr++;
 567                                 total += e->hit_count;
 568
 569                                 if (++count >= MAX_TO_AVERAGE)
 570                                         break;
 571                         }
 572                 }
 573
 574                 mq->promote_threshold = nr ? total / nr : 1;
 575                 if (mq->promote_threshold * nr < total)
 576                         mq->promote_threshold++;
 577         }
 578 }
 579
 580 /*
 581  * Whenever we use an entry we bump up it's hit counter, and push it to the
 582  * back to it's current level.
 583  */
 584 static void requeue_and_update_tick(struct mq_policy *mq, struct entry *e)
 585 {
 586         if (updated_this_tick(mq, e))
 587                 return;
 588
 589         e->hit_count++;
 590         mq->hit_count++;
 591         check_generation(mq);
 592
 593         /* generation adjustment, to stop the counts increasing forever. */
 594         /* FIXME: divide? */
 595         /* e->hit_count -= min(e->hit_count - 1, mq->generation - e->generation); */
 596         e->generation = mq->generation;
 597
 598         del(mq, e);
 599         push(mq, e);
 600 }
 601
 602 /*
 603  * Demote the least recently used entry from the cache to the pre_cache.
 604  * Returns the new cache entry to use, and the old origin block it was
 605  * mapped to.
 606  *
 607  * We drop the hit count on the demoted entry back to 1 to stop it bouncing
 608  * straight back into the cache if it's subsequently hit.  There are
 609  * various options here, and more experimentation would be good:
 610  *
 611  * - just forget about the demoted entry completely (ie. don't insert it
 612      into the pre_cache).
 613  * - divide the hit count rather that setting to some hard coded value.
 614  * - set the hit count to a hard coded value other than 1, eg, is it better
 615  *   if it goes in at level 2?
 616  */
 617 static int demote_cblock(struct mq_policy *mq, dm_oblock_t *oblock)
 618 {
 619         struct entry *demoted = pop(mq, &mq->cache_clean);
 620
 621         if (!demoted)
 622                 /*
 623                  * We could get a block from mq->cache_dirty, but that
 624                  * would add extra latency to the triggering bio as it
 625                  * waits for the writeback.  Better to not promote this
 626                  * time and hope there's a clean block next time this block
 627                  * is hit.
 628                  */
 629                 return -ENOSPC;
 630
 631         *oblock = demoted->oblock;
 632         free_entry(&mq->cache_pool, demoted);
 633
 634         /*
 635          * We used to put the demoted block into the pre-cache, but I think
 636          * it's simpler to just let it work it's way up from zero again.
 637          * Stops blocks flickering in and out of the cache.
 638          */
 639
 640         return 0;
 641 }
 642
 643 /*
 644  * We modify the basic promotion_threshold depending on the specific io.
 645  *
 646  * If the origin block has been discarded then there's no cost to copy it
 647  * to the cache.
 648  *
 649  * We bias towards reads, since they can be demoted at no cost if they
 650  * haven't been dirtied.
 651  */
 652 static unsigned adjusted_promote_threshold(struct mq_policy *mq,
 653                                            bool discarded_oblock, int data_dir)
 654 {
 655         if (data_dir == READ)
 656                 return mq->promote_threshold + mq->read_promote_adjustment;
 657
 658         if (discarded_oblock && (any_free_cblocks(mq) || any_clean_cblocks(mq))) {
 659                 /*
 660                  * We don't need to do any copying at all, so give this a
 661                  * very low threshold.
 662                  */
 663                 return mq->discard_promote_adjustment;
 664         }
 665
 666         return mq->promote_threshold + mq->write_promote_adjustment;
 667 }
 668
 669 static bool should_promote(struct mq_policy *mq, struct entry *e,
 670                            bool discarded_oblock, int data_dir)
 671 {
 672         return e->hit_count >=
 673                 adjusted_promote_threshold(mq, discarded_oblock, data_dir);
 674 }
 675
 676 static int cache_entry_found(struct mq_policy *mq,
 677                              struct entry *e,
 678                              struct policy_result *result)
 679 {
 680         requeue_and_update_tick(mq, e);
 681
 682         if (in_cache(mq, e)) {
 683                 result->op = POLICY_HIT;
 684                 result->cblock = infer_cblock(&mq->cache_pool, e);
 685         }
 686
 687         return 0;
 688 }
 689
 690 /*
 691  * Moves an entry from the pre_cache to the cache.  The main work is
 692  * finding which cache block to use.
 693  */
 694 static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
 695                               struct policy_result *result)
 696 {
 697         int r;
 698         struct entry *new_e;
 699
 700         /* Ensure there's a free cblock in the cache */
 701         if (epool_empty(&mq->cache_pool)) {
 702                 result->op = POLICY_REPLACE;
 703                 r = demote_cblock(mq, &result->old_oblock);
 704                 if (r) {
 705                         result->op = POLICY_MISS;
 706                         return 0;
 707                 }
 708         } else
 709                 result->op = POLICY_NEW;
 710
 711         new_e = alloc_entry(&mq->cache_pool);
 712         BUG_ON(!new_e);
 713
 714         new_e->oblock = e->oblock;
 715         new_e->dirty = false;
 716         new_e->hit_count = e->hit_count;
 717         new_e->generation = e->generation;
 718         new_e->tick = e->tick;
 719
 720         del(mq, e);
 721         free_entry(&mq->pre_cache_pool, e);
 722         push(mq, new_e);
 723
 724         result->cblock = infer_cblock(&mq->cache_pool, new_e);
 725
 726         return 0;
 727 }
 728
 729 static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e,
 730                                  bool can_migrate, bool discarded_oblock,
 731                                  int data_dir, struct policy_result *result)
 732 {
 733         int r = 0;
 734         bool updated = updated_this_tick(mq, e);
 735
 736         if ((!discarded_oblock && updated) ||
 737             !should_promote(mq, e, discarded_oblock, data_dir)) {
 738                 requeue_and_update_tick(mq, e);
 739                 result->op = POLICY_MISS;
 740
 741         } else if (!can_migrate)
 742                 r = -EWOULDBLOCK;
 743
 744         else {
 745                 requeue_and_update_tick(mq, e);
 746                 r = pre_cache_to_cache(mq, e, result);
 747         }
 748
 749         return r;
 750 }
 751
 752 static void insert_in_pre_cache(struct mq_policy *mq,
 753                                 dm_oblock_t oblock)
 754 {
 755         struct entry *e = alloc_entry(&mq->pre_cache_pool);
 756
 757         if (!e)
 758                 /*
 759                  * There's no spare entry structure, so we grab the least
 760                  * used one from the pre_cache.
 761                  */
 762                 e = pop(mq, &mq->pre_cache);
 763
 764         if (unlikely(!e)) {
 765                 DMWARN("couldn't pop from pre cache");
 766                 return;
 767         }
 768
 769         e->dirty = false;
 770         e->oblock = oblock;
 771         e->hit_count = 1;
 772         e->generation = mq->generation;
 773         push(mq, e);
 774 }
 775
 776 static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
 777                             struct policy_result *result)
 778 {
 779         int r;
 780         struct entry *e;
 781
 782         if (epool_empty(&mq->cache_pool)) {
 783                 result->op = POLICY_REPLACE;
 784                 r = demote_cblock(mq, &result->old_oblock);
 785                 if (unlikely(r)) {
 786                         result->op = POLICY_MISS;
 787                         insert_in_pre_cache(mq, oblock);
 788                         return;
 789                 }
 790
 791                 /*
 792                  * This will always succeed, since we've just demoted.
 793                  */
 794                 e = alloc_entry(&mq->cache_pool);
 795                 BUG_ON(!e);
 796
 797         } else {
 798                 e = alloc_entry(&mq->cache_pool);
 799                 result->op = POLICY_NEW;
 800         }
 801
 802         e->oblock = oblock;
 803         e->dirty = false;
 804         e->hit_count = 1;
 805         e->generation = mq->generation;
 806         push(mq, e);
 807
 808         result->cblock = infer_cblock(&mq->cache_pool, e);
 809 }
 810
 811 static int no_entry_found(struct mq_policy *mq, dm_oblock_t oblock,
 812                           bool can_migrate, bool discarded_oblock,
 813                           int data_dir, struct policy_result *result)
 814 {
 815         if (adjusted_promote_threshold(mq, discarded_oblock, data_dir) <= 1) {
 816                 if (can_migrate)
 817                         insert_in_cache(mq, oblock, result);
 818                 else
 819                         return -EWOULDBLOCK;
 820         } else {
 821                 insert_in_pre_cache(mq, oblock);
 822                 result->op = POLICY_MISS;
 823         }
 824
 825         return 0;
 826 }
 827
 828 /*
 829  * Looks the oblock up in the hash table, then decides whether to put in
 830  * pre_cache, or cache etc.
 831  */
 832 static int map(struct mq_policy *mq, dm_oblock_t oblock,
 833                bool can_migrate, bool discarded_oblock,
 834                int data_dir, struct policy_result *result)
 835 {
 836         int r = 0;
 837         struct entry *e = hash_lookup(mq, oblock);
 838
 839         if (e && in_cache(mq, e))
 840                 r = cache_entry_found(mq, e, result);
 841
 842         else if (iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL)
 843                 result->op = POLICY_MISS;
 844
 845         else if (e)
 846                 r = pre_cache_entry_found(mq, e, can_migrate, discarded_oblock,
 847                                           data_dir, result);
 848
 849         else
 850                 r = no_entry_found(mq, oblock, can_migrate, discarded_oblock,
 851                                    data_dir, result);
 852
 853         if (r == -EWOULDBLOCK)
 854                 result->op = POLICY_MISS;
 855
 856         return r;
 857 }
 858
 859 /*----------------------------------------------------------------*/
 860
 861 /*
 862  * Public interface, via the policy struct.  See dm-cache-policy.h for a
 863  * description of these.
 864  */
 865
 866 static struct mq_policy *to_mq_policy(struct dm_cache_policy *p)
 867 {
 868         return container_of(p, struct mq_policy, policy);
 869 }
 870
 871 static void mq_destroy(struct dm_cache_policy *p)
 872 {
 873         struct mq_policy *mq = to_mq_policy(p);
 874
 875         vfree(mq->table);
 876         epool_exit(&mq->cache_pool);
 877         epool_exit(&mq->pre_cache_pool);
 878         kfree(mq);
 879 }
 880
 881 static void copy_tick(struct mq_policy *mq)
 882 {
 883         unsigned long flags;
 884
 885         spin_lock_irqsave(&mq->tick_lock, flags);
 886         mq->tick = mq->tick_protected;
 887         spin_unlock_irqrestore(&mq->tick_lock, flags);
 888 }
 889
 890 static int mq_map(struct dm_cache_policy *p, dm_oblock_t oblock,
 891                   bool can_block, bool can_migrate, bool discarded_oblock,
 892                   struct bio *bio, struct policy_result *result)
 893 {
 894         int r;
 895         struct mq_policy *mq = to_mq_policy(p);
 896
 897         result->op = POLICY_MISS;
 898
 899         if (can_block)
 900                 mutex_lock(&mq->lock);
 901         else if (!mutex_trylock(&mq->lock))
 902                 return -EWOULDBLOCK;
 903
 904         copy_tick(mq);
 905
 906         iot_examine_bio(&mq->tracker, bio);
 907         r = map(mq, oblock, can_migrate, discarded_oblock,
 908                 bio_data_dir(bio), result);
 909
 910         mutex_unlock(&mq->lock);
 911
 912         return r;
 913 }
 914
 915 static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
 916 {
 917         int r;
 918         struct mq_policy *mq = to_mq_policy(p);
 919         struct entry *e;
 920
 921         if (!mutex_trylock(&mq->lock))
 922                 return -EWOULDBLOCK;
 923
 924         e = hash_lookup(mq, oblock);
 925         if (e && in_cache(mq, e)) {
 926                 *cblock = infer_cblock(&mq->cache_pool, e);
 927                 r = 0;
 928         } else
 929                 r = -ENOENT;
 930
 931         mutex_unlock(&mq->lock);
 932
 933         return r;
 934 }
 935
 936 static void __mq_set_clear_dirty(struct mq_policy *mq, dm_oblock_t oblock, bool set)
 937 {
 938         struct entry *e;
 939
 940         e = hash_lookup(mq, oblock);
 941         BUG_ON(!e || !in_cache(mq, e));
 942
 943         del(mq, e);
 944         e->dirty = set;
 945         push(mq, e);
 946 }
 947
 948 static void mq_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
 949 {
 950         struct mq_policy *mq = to_mq_policy(p);
 951
 952         mutex_lock(&mq->lock);
 953         __mq_set_clear_dirty(mq, oblock, true);
 954         mutex_unlock(&mq->lock);
 955 }
 956
 957 static void mq_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
 958 {
 959         struct mq_policy *mq = to_mq_policy(p);
 960
 961         mutex_lock(&mq->lock);
 962         __mq_set_clear_dirty(mq, oblock, false);
 963         mutex_unlock(&mq->lock);
 964 }
 965
 966 static int mq_load_mapping(struct dm_cache_policy *p,
 967                            dm_oblock_t oblock, dm_cblock_t cblock,
 968                            uint32_t hint, bool hint_valid)
 969 {
 970         struct mq_policy *mq = to_mq_policy(p);
 971         struct entry *e;
 972
 973         e = alloc_particular_entry(&mq->cache_pool, cblock);
 974         e->oblock = oblock;
 975         e->dirty = false;       /* this gets corrected in a minute */
 976         e->hit_count = hint_valid ? hint : 1;
 977         e->generation = mq->generation;
 978         push(mq, e);
 979
 980         return 0;
 981 }
 982
 983 static int mq_save_hints(struct mq_policy *mq, struct queue *q,
 984                          policy_walk_fn fn, void *context)
 985 {
 986         int r;
 987         unsigned level;
 988         struct entry *e;
 989
 990         for (level = 0; level < NR_QUEUE_LEVELS; level++)
 991                 list_for_each_entry(e, q->qs + level, list) {
 992                         r = fn(context, infer_cblock(&mq->cache_pool, e),
 993                                e->oblock, e->hit_count);
 994                         if (r)
 995                                 return r;
 996                 }
 997
 998         return 0;
 999 }
1000
1001 static int mq_walk_mappings(struct dm_cache_policy *p, policy_walk_fn fn,
1002                             void *context)
1003 {
1004         struct mq_policy *mq = to_mq_policy(p);
1005         int r = 0;
1006
1007         mutex_lock(&mq->lock);
1008
1009         r = mq_save_hints(mq, &mq->cache_clean, fn, context);
1010         if (!r)
1011                 r = mq_save_hints(mq, &mq->cache_dirty, fn, context);
1012
1013         mutex_unlock(&mq->lock);
1014
1015         return r;
1016 }
1017
1018 static void __remove_mapping(struct mq_policy *mq, dm_oblock_t oblock)
1019 {
1020         struct entry *e;
1021
1022         e = hash_lookup(mq, oblock);
1023         BUG_ON(!e || !in_cache(mq, e));
1024
1025         del(mq, e);
1026         free_entry(&mq->cache_pool, e);
1027 }
1028
1029 static void mq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
1030 {
1031         struct mq_policy *mq = to_mq_policy(p);
1032
1033         mutex_lock(&mq->lock);
1034         __remove_mapping(mq, oblock);
1035         mutex_unlock(&mq->lock);
1036 }
1037
1038 static int __remove_cblock(struct mq_policy *mq, dm_cblock_t cblock)
1039 {
1040         struct entry *e = epool_find(&mq->cache_pool, cblock);
1041
1042         if (!e)
1043                 return -ENODATA;
1044
1045         del(mq, e);
1046         free_entry(&mq->cache_pool, e);
1047
1048         return 0;
1049 }
1050
1051 static int mq_remove_cblock(struct dm_cache_policy *p, dm_cblock_t cblock)
1052 {
1053         int r;
1054         struct mq_policy *mq = to_mq_policy(p);
1055
1056         mutex_lock(&mq->lock);
1057         r = __remove_cblock(mq, cblock);
1058         mutex_unlock(&mq->lock);
1059
1060         return r;
1061 }
1062
1063 static int __mq_writeback_work(struct mq_policy *mq, dm_oblock_t *oblock,
1064                               dm_cblock_t *cblock)
1065 {
1066         struct entry *e = pop(mq, &mq->cache_dirty);
1067
1068         if (!e)
1069                 return -ENODATA;
1070
1071         *oblock = e->oblock;
1072         *cblock = infer_cblock(&mq->cache_pool, e);
1073         e->dirty = false;
1074         push(mq, e);
1075
1076         return 0;
1077 }
1078
1079 static int mq_writeback_work(struct dm_cache_policy *p, dm_oblock_t *oblock,
1080                              dm_cblock_t *cblock)
1081 {
1082         int r;
1083         struct mq_policy *mq = to_mq_policy(p);
1084
1085         mutex_lock(&mq->lock);
1086         r = __mq_writeback_work(mq, oblock, cblock);
1087         mutex_unlock(&mq->lock);
1088
1089         return r;
1090 }
1091
1092 static void __force_mapping(struct mq_policy *mq,
1093                             dm_oblock_t current_oblock, dm_oblock_t new_oblock)
1094 {
1095         struct entry *e = hash_lookup(mq, current_oblock);
1096
1097         if (e && in_cache(mq, e)) {
1098                 del(mq, e);
1099                 e->oblock = new_oblock;
1100                 e->dirty = true;
1101                 push(mq, e);
1102         }
1103 }
1104
1105 static void mq_force_mapping(struct dm_cache_policy *p,
1106                              dm_oblock_t current_oblock, dm_oblock_t new_oblock)
1107 {
1108         struct mq_policy *mq = to_mq_policy(p);
1109
1110         mutex_lock(&mq->lock);
1111         __force_mapping(mq, current_oblock, new_oblock);
1112         mutex_unlock(&mq->lock);
1113 }
1114
1115 static dm_cblock_t mq_residency(struct dm_cache_policy *p)
1116 {
1117         dm_cblock_t r;
1118         struct mq_policy *mq = to_mq_policy(p);
1119
1120         mutex_lock(&mq->lock);
1121         r = to_cblock(mq->cache_pool.nr_allocated);
1122         mutex_unlock(&mq->lock);
1123
1124         return r;
1125 }
1126
1127 static void mq_tick(struct dm_cache_policy *p)
1128 {
1129         struct mq_policy *mq = to_mq_policy(p);
1130         unsigned long flags;
1131
1132         spin_lock_irqsave(&mq->tick_lock, flags);
1133         mq->tick_protected++;
1134         spin_unlock_irqrestore(&mq->tick_lock, flags);
1135 }
1136
1137 static int mq_set_config_value(struct dm_cache_policy *p,
1138                                const char *key, const char *value)
1139 {
1140         struct mq_policy *mq = to_mq_policy(p);
1141         unsigned long tmp;
1142
1143         if (kstrtoul(value, 10, &tmp))
1144                 return -EINVAL;
1145
1146         if (!strcasecmp(key, "random_threshold")) {
1147                 mq->tracker.thresholds[PATTERN_RANDOM] = tmp;
1148
1149         } else if (!strcasecmp(key, "sequential_threshold")) {
1150                 mq->tracker.thresholds[PATTERN_SEQUENTIAL] = tmp;
1151
1152         } else if (!strcasecmp(key, "discard_promote_adjustment"))
1153                 mq->discard_promote_adjustment = tmp;
1154
1155         else if (!strcasecmp(key, "read_promote_adjustment"))
1156                 mq->read_promote_adjustment = tmp;
1157
1158         else if (!strcasecmp(key, "write_promote_adjustment"))
1159                 mq->write_promote_adjustment = tmp;
1160
1161         else
1162                 return -EINVAL;
1163
1164         return 0;
1165 }
1166
1167 static int mq_emit_config_values(struct dm_cache_policy *p, char *result, unsigned maxlen)
1168 {
1169         ssize_t sz = 0;
1170         struct mq_policy *mq = to_mq_policy(p);
1171
1172         DMEMIT("10 random_threshold %u "
1173                "sequential_threshold %u "
1174                "discard_promote_adjustment %u "
1175                "read_promote_adjustment %u "
1176                "write_promote_adjustment %u",
1177                mq->tracker.thresholds[PATTERN_RANDOM],
1178                mq->tracker.thresholds[PATTERN_SEQUENTIAL],
1179                mq->discard_promote_adjustment,
1180                mq->read_promote_adjustment,
1181                mq->write_promote_adjustment);
1182
1183         return 0;
1184 }
1185
1186 /* Init the policy plugin interface function pointers. */
1187 static void init_policy_functions(struct mq_policy *mq)
1188 {
1189         mq->policy.destroy = mq_destroy;
1190         mq->policy.map = mq_map;
1191         mq->policy.lookup = mq_lookup;
1192         mq->policy.set_dirty = mq_set_dirty;
1193         mq->policy.clear_dirty = mq_clear_dirty;
1194         mq->policy.load_mapping = mq_load_mapping;
1195         mq->policy.walk_mappings = mq_walk_mappings;
1196         mq->policy.remove_mapping = mq_remove_mapping;
1197         mq->policy.remove_cblock = mq_remove_cblock;
1198         mq->policy.writeback_work = mq_writeback_work;
1199         mq->policy.force_mapping = mq_force_mapping;
1200         mq->policy.residency = mq_residency;
1201         mq->policy.tick = mq_tick;
1202         mq->policy.emit_config_values = mq_emit_config_values;
1203         mq->policy.set_config_value = mq_set_config_value;
1204 }
1205
1206 static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
1207                                          sector_t origin_size,
1208                                          sector_t cache_block_size)
1209 {
1210         struct mq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);
1211
1212         if (!mq)
1213                 return NULL;
1214
1215         init_policy_functions(mq);
1216         iot_init(&mq->tracker, SEQUENTIAL_THRESHOLD_DEFAULT, RANDOM_THRESHOLD_DEFAULT);
1217         mq->cache_size = cache_size;
1218
1219         if (epool_init(&mq->pre_cache_pool, from_cblock(cache_size))) {
1220                 DMERR("couldn't initialize pool of pre-cache entries");
1221                 goto bad_pre_cache_init;
1222         }
1223
1224         if (epool_init(&mq->cache_pool, from_cblock(cache_size))) {
1225                 DMERR("couldn't initialize pool of cache entries");
1226                 goto bad_cache_init;
1227         }
1228
1229         mq->tick_protected = 0;
1230         mq->tick = 0;
1231         mq->hit_count = 0;
1232         mq->generation = 0;
1233         mq->promote_threshold = 0;
1234         mq->discard_promote_adjustment = DEFAULT_DISCARD_PROMOTE_ADJUSTMENT;
1235         mq->read_promote_adjustment = DEFAULT_READ_PROMOTE_ADJUSTMENT;
1236         mq->write_promote_adjustment = DEFAULT_WRITE_PROMOTE_ADJUSTMENT;
1237         mutex_init(&mq->lock);
1238         spin_lock_init(&mq->tick_lock);
1239
1240         queue_init(&mq->pre_cache);
1241         queue_init(&mq->cache_clean);
1242         queue_init(&mq->cache_dirty);
1243
1244         mq->generation_period = max((unsigned) from_cblock(cache_size), 1024U);
1245
1246         mq->nr_buckets = next_power(from_cblock(cache_size) / 2, 16);
1247         mq->hash_bits = ffs(mq->nr_buckets) - 1;
1248         mq->table = vzalloc(sizeof(*mq->table) * mq->nr_buckets);
1249         if (!mq->table)
1250                 goto bad_alloc_table;
1251
1252         return &mq->policy;
1253
1254 bad_alloc_table:
1255         epool_exit(&mq->cache_pool);
1256 bad_cache_init:
1257         epool_exit(&mq->pre_cache_pool);
1258 bad_pre_cache_init:
1259         kfree(mq);
1260
1261         return NULL;
1262 }
1263
1264 /*----------------------------------------------------------------*/
1265
1266 static struct dm_cache_policy_type mq_policy_type = {
1267         .name = "mq",
1268         .version = {1, 2, 0},
1269         .hint_size = 4,
1270         .owner = THIS_MODULE,
1271         .create = mq_create
1272 };
1273
1274 static struct dm_cache_policy_type default_policy_type = {
1275         .name = "default",
1276         .version = {1, 2, 0},
1277         .hint_size = 4,
1278         .owner = THIS_MODULE,
1279         .create = mq_create,
1280         .real = &mq_policy_type
1281 };
1282
1283 static int __init mq_init(void)
1284 {
1285         int r;
1286
1287         mq_entry_cache = kmem_cache_create("dm_mq_policy_cache_entry",
1288                                            sizeof(struct entry),
1289                                            __alignof__(struct entry),
1290                                            0, NULL);
1291         if (!mq_entry_cache)
1292                 goto bad;
1293
1294         r = dm_cache_policy_register(&mq_policy_type);
1295         if (r) {
1296                 DMERR("register failed %d", r);
1297                 goto bad_register_mq;
1298         }
1299
1300         r = dm_cache_policy_register(&default_policy_type);
1301         if (!r) {
1302                 DMINFO("version %u.%u.%u loaded",
1303                        mq_policy_type.version[0],
1304                        mq_policy_type.version[1],
1305                        mq_policy_type.version[2]);
1306                 return 0;
1307         }
1308
1309         DMERR("register failed (as default) %d", r);
1310
1311         dm_cache_policy_unregister(&mq_policy_type);
1312 bad_register_mq:
1313         kmem_cache_destroy(mq_entry_cache);
1314 bad:
1315         return -ENOMEM;
1316 }
1317
1318 static void __exit mq_exit(void)
1319 {
1320         dm_cache_policy_unregister(&mq_policy_type);
1321         dm_cache_policy_unregister(&default_policy_type);
1322
1323         kmem_cache_destroy(mq_entry_cache);
1324 }
1325
1326 module_init(mq_init);
1327 module_exit(mq_exit);
1328
1329 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
1330 MODULE_LICENSE("GPL");
1331 MODULE_DESCRIPTION("mq cache policy");
1332
1333 MODULE_ALIAS("dm-cache-default");