drivers/md/persistent-data/dm-space-map-metadata.c

   1 /*
   2  * Copyright (C) 2011 Red Hat, Inc.
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-space-map.h"
   8 #include "dm-space-map-common.h"
   9 #include "dm-space-map-metadata.h"
  10
  11 #include <linux/list.h>
  12 #include <linux/slab.h>
  13 #include <linux/device-mapper.h>
  14
  15 #define DM_MSG_PREFIX "space map metadata"
  16
  17 /*----------------------------------------------------------------*/
  18
  19 /*
  20  * An edge triggered threshold.
  21  */
  22 struct threshold {
  23         bool threshold_set;
  24         bool value_set;
  25         dm_block_t threshold;
  26         dm_block_t current_value;
  27         dm_sm_threshold_fn fn;
  28         void *context;
  29 };
  30
  31 static void threshold_init(struct threshold *t)
  32 {
  33         t->threshold_set = false;
  34         t->value_set = false;
  35 }
  36
  37 static void set_threshold(struct threshold *t, dm_block_t value,
  38                           dm_sm_threshold_fn fn, void *context)
  39 {
  40         t->threshold_set = true;
  41         t->threshold = value;
  42         t->fn = fn;
  43         t->context = context;
  44 }
  45
  46 static bool below_threshold(struct threshold *t, dm_block_t value)
  47 {
  48         return t->threshold_set && value <= t->threshold;
  49 }
  50
  51 static bool threshold_already_triggered(struct threshold *t)
  52 {
  53         return t->value_set && below_threshold(t, t->current_value);
  54 }
  55
  56 static void check_threshold(struct threshold *t, dm_block_t value)
  57 {
  58         if (below_threshold(t, value) &&
  59             !threshold_already_triggered(t))
  60                 t->fn(t->context);
  61
  62         t->value_set = true;
  63         t->current_value = value;
  64 }
  65
  66 /*----------------------------------------------------------------*/
  67
  68 /*
  69  * Space map interface.
  70  *
  71  * The low level disk format is written using the standard btree and
  72  * transaction manager.  This means that performing disk operations may
  73  * cause us to recurse into the space map in order to allocate new blocks.
  74  * For this reason we have a pool of pre-allocated blocks large enough to
  75  * service any metadata_ll_disk operation.
  76  */
  77
  78 /*
  79  * FIXME: we should calculate this based on the size of the device.
  80  * Only the metadata space map needs this functionality.
  81  */
  82 #define MAX_RECURSIVE_ALLOCATIONS 1024
  83
  84 enum block_op_type {
  85         BOP_INC,
  86         BOP_DEC
  87 };
  88
  89 struct block_op {
  90         enum block_op_type type;
  91         dm_block_t block;
  92 };
  93
  94 struct bop_ring_buffer {
  95         unsigned begin;
  96         unsigned end;
  97         struct block_op bops[MAX_RECURSIVE_ALLOCATIONS + 1];
  98 };
  99
 100 static void brb_init(struct bop_ring_buffer *brb)
 101 {
 102         brb->begin = 0;
 103         brb->end = 0;
 104 }
 105
 106 static bool brb_empty(struct bop_ring_buffer *brb)
 107 {
 108         return brb->begin == brb->end;
 109 }
 110
 111 static unsigned brb_next(struct bop_ring_buffer *brb, unsigned old)
 112 {
 113         unsigned r = old + 1;
 114         return (r >= (sizeof(brb->bops) / sizeof(*brb->bops))) ? 0 : r;
 115 }
 116
 117 static int brb_push(struct bop_ring_buffer *brb,
 118                     enum block_op_type type, dm_block_t b)
 119 {
 120         struct block_op *bop;
 121         unsigned next = brb_next(brb, brb->end);
 122
 123         /*
 124          * We don't allow the last bop to be filled, this way we can
 125          * differentiate between full and empty.
 126          */
 127         if (next == brb->begin)
 128                 return -ENOMEM;
 129
 130         bop = brb->bops + brb->end;
 131         bop->type = type;
 132         bop->block = b;
 133
 134         brb->end = next;
 135
 136         return 0;
 137 }
 138
 139 static int brb_pop(struct bop_ring_buffer *brb, struct block_op *result)
 140 {
 141         struct block_op *bop;
 142
 143         if (brb_empty(brb))
 144                 return -ENODATA;
 145
 146         bop = brb->bops + brb->begin;
 147         result->type = bop->type;
 148         result->block = bop->block;
 149
 150         brb->begin = brb_next(brb, brb->begin);
 151
 152         return 0;
 153 }
 154
 155 /*----------------------------------------------------------------*/
 156
 157 struct sm_metadata {
 158         struct dm_space_map sm;
 159
 160         struct ll_disk ll;
 161         struct ll_disk old_ll;
 162
 163         dm_block_t begin;
 164
 165         unsigned recursion_count;
 166         unsigned allocated_this_transaction;
 167         struct bop_ring_buffer uncommitted;
 168
 169         struct threshold threshold;
 170 };
 171
 172 static int add_bop(struct sm_metadata *smm, enum block_op_type type, dm_block_t b)
 173 {
 174         int r = brb_push(&smm->uncommitted, type, b);
 175
 176         if (r) {
 177                 DMERR("too many recursive allocations");
 178                 return -ENOMEM;
 179         }
 180
 181         return 0;
 182 }
 183
 184 static int commit_bop(struct sm_metadata *smm, struct block_op *op)
 185 {
 186         int r = 0;
 187         enum allocation_event ev;
 188
 189         switch (op->type) {
 190         case BOP_INC:
 191                 r = sm_ll_inc(&smm->ll, op->block, &ev);
 192                 break;
 193
 194         case BOP_DEC:
 195                 r = sm_ll_dec(&smm->ll, op->block, &ev);
 196                 break;
 197         }
 198
 199         return r;
 200 }
 201
 202 static void in(struct sm_metadata *smm)
 203 {
 204         smm->recursion_count++;
 205 }
 206
 207 static int out(struct sm_metadata *smm)
 208 {
 209         int r = 0;
 210
 211         /*
 212          * If we're not recursing then very bad things are happening.
 213          */
 214         if (!smm->recursion_count) {
 215                 DMERR("lost track of recursion depth");
 216                 return -ENOMEM;
 217         }
 218
 219         if (smm->recursion_count == 1) {
 220                 while (!brb_empty(&smm->uncommitted)) {
 221                         struct block_op bop;
 222
 223                         r = brb_pop(&smm->uncommitted, &bop);
 224                         if (r) {
 225                                 DMERR("bug in bop ring buffer");
 226                                 break;
 227                         }
 228
 229                         r = commit_bop(smm, &bop);
 230                         if (r)
 231                                 break;
 232                 }
 233         }
 234
 235         smm->recursion_count--;
 236
 237         return r;
 238 }
 239
 240 /*
 241  * When using the out() function above, we often want to combine an error
 242  * code for the operation run in the recursive context with that from
 243  * out().
 244  */
 245 static int combine_errors(int r1, int r2)
 246 {
 247         return r1 ? r1 : r2;
 248 }
 249
 250 static int recursing(struct sm_metadata *smm)
 251 {
 252         return smm->recursion_count;
 253 }
 254
 255 static void sm_metadata_destroy(struct dm_space_map *sm)
 256 {
 257         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 258
 259         kfree(smm);
 260 }
 261
 262 static int sm_metadata_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
 263 {
 264         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 265
 266         *count = smm->ll.nr_blocks;
 267
 268         return 0;
 269 }
 270
 271 static int sm_metadata_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
 272 {
 273         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 274
 275         *count = smm->old_ll.nr_blocks - smm->old_ll.nr_allocated -
 276                  smm->allocated_this_transaction;
 277
 278         return 0;
 279 }
 280
 281 static int sm_metadata_get_count(struct dm_space_map *sm, dm_block_t b,
 282                                  uint32_t *result)
 283 {
 284         int r;
 285         unsigned i;
 286         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 287         unsigned adjustment = 0;
 288
 289         /*
 290          * We may have some uncommitted adjustments to add.  This list
 291          * should always be really short.
 292          */
 293         for (i = smm->uncommitted.begin;
 294              i != smm->uncommitted.end;
 295              i = brb_next(&smm->uncommitted, i)) {
 296                 struct block_op *op = smm->uncommitted.bops + i;
 297
 298                 if (op->block != b)
 299                         continue;
 300
 301                 switch (op->type) {
 302                 case BOP_INC:
 303                         adjustment++;
 304                         break;
 305
 306                 case BOP_DEC:
 307                         adjustment--;
 308                         break;
 309                 }
 310         }
 311
 312         r = sm_ll_lookup(&smm->ll, b, result);
 313         if (r)
 314                 return r;
 315
 316         *result += adjustment;
 317
 318         return 0;
 319 }
 320
 321 static int sm_metadata_count_is_more_than_one(struct dm_space_map *sm,
 322                                               dm_block_t b, int *result)
 323 {
 324         int r, adjustment = 0;
 325         unsigned i;
 326         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 327         uint32_t rc;
 328
 329         /*
 330          * We may have some uncommitted adjustments to add.  This list
 331          * should always be really short.
 332          */
 333         for (i = smm->uncommitted.begin;
 334              i != smm->uncommitted.end;
 335              i = brb_next(&smm->uncommitted, i)) {
 336
 337                 struct block_op *op = smm->uncommitted.bops + i;
 338
 339                 if (op->block != b)
 340                         continue;
 341
 342                 switch (op->type) {
 343                 case BOP_INC:
 344                         adjustment++;
 345                         break;
 346
 347                 case BOP_DEC:
 348                         adjustment--;
 349                         break;
 350                 }
 351         }
 352
 353         if (adjustment > 1) {
 354                 *result = 1;
 355                 return 0;
 356         }
 357
 358         r = sm_ll_lookup_bitmap(&smm->ll, b, &rc);
 359         if (r)
 360                 return r;
 361
 362         if (rc == 3)
 363                 /*
 364                  * We err on the side of caution, and always return true.
 365                  */
 366                 *result = 1;
 367         else
 368                 *result = rc + adjustment > 1;
 369
 370         return 0;
 371 }
 372
 373 static int sm_metadata_set_count(struct dm_space_map *sm, dm_block_t b,
 374                                  uint32_t count)
 375 {
 376         int r, r2;
 377         enum allocation_event ev;
 378         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 379
 380         if (smm->recursion_count) {
 381                 DMERR("cannot recurse set_count()");
 382                 return -EINVAL;
 383         }
 384
 385         in(smm);
 386         r = sm_ll_insert(&smm->ll, b, count, &ev);
 387         r2 = out(smm);
 388
 389         return combine_errors(r, r2);
 390 }
 391
 392 static int sm_metadata_inc_block(struct dm_space_map *sm, dm_block_t b)
 393 {
 394         int r, r2 = 0;
 395         enum allocation_event ev;
 396         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 397
 398         if (recursing(smm))
 399                 r = add_bop(smm, BOP_INC, b);
 400         else {
 401                 in(smm);
 402                 r = sm_ll_inc(&smm->ll, b, &ev);
 403                 r2 = out(smm);
 404         }
 405
 406         return combine_errors(r, r2);
 407 }
 408
 409 static int sm_metadata_dec_block(struct dm_space_map *sm, dm_block_t b)
 410 {
 411         int r, r2 = 0;
 412         enum allocation_event ev;
 413         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 414
 415         if (recursing(smm))
 416                 r = add_bop(smm, BOP_DEC, b);
 417         else {
 418                 in(smm);
 419                 r = sm_ll_dec(&smm->ll, b, &ev);
 420                 r2 = out(smm);
 421         }
 422
 423         return combine_errors(r, r2);
 424 }
 425
 426 static int sm_metadata_new_block_(struct dm_space_map *sm, dm_block_t *b)
 427 {
 428         int r, r2 = 0;
 429         enum allocation_event ev;
 430         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 431
 432         r = sm_ll_find_free_block(&smm->old_ll, smm->begin, smm->old_ll.nr_blocks, b);
 433         if (r)
 434                 return r;
 435
 436         smm->begin = *b + 1;
 437
 438         if (recursing(smm))
 439                 r = add_bop(smm, BOP_INC, *b);
 440         else {
 441                 in(smm);
 442                 r = sm_ll_inc(&smm->ll, *b, &ev);
 443                 r2 = out(smm);
 444         }
 445
 446         if (!r)
 447                 smm->allocated_this_transaction++;
 448
 449         return combine_errors(r, r2);
 450 }
 451
 452 static int sm_metadata_new_block(struct dm_space_map *sm, dm_block_t *b)
 453 {
 454         dm_block_t count;
 455         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 456
 457         int r = sm_metadata_new_block_(sm, b);
 458         if (r) {
 459                 DMERR("unable to allocate new metadata block");
 460                 return r;
 461         }
 462
 463         r = sm_metadata_get_nr_free(sm, &count);
 464         if (r) {
 465                 DMERR("couldn't get free block count");
 466                 return r;
 467         }
 468
 469         check_threshold(&smm->threshold, count);
 470
 471         return r;
 472 }
 473
 474 static int sm_metadata_commit(struct dm_space_map *sm)
 475 {
 476         int r;
 477         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 478
 479         r = sm_ll_commit(&smm->ll);
 480         if (r)
 481                 return r;
 482
 483         memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
 484         smm->begin = 0;
 485         smm->allocated_this_transaction = 0;
 486
 487         return 0;
 488 }
 489
 490 static int sm_metadata_register_threshold_callback(struct dm_space_map *sm,
 491                                                    dm_block_t threshold,
 492                                                    dm_sm_threshold_fn fn,
 493                                                    void *context)
 494 {
 495         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 496
 497         set_threshold(&smm->threshold, threshold, fn, context);
 498
 499         return 0;
 500 }
 501
 502 static int sm_metadata_root_size(struct dm_space_map *sm, size_t *result)
 503 {
 504         *result = sizeof(struct disk_sm_root);
 505
 506         return 0;
 507 }
 508
 509 static int sm_metadata_copy_root(struct dm_space_map *sm, void *where_le, size_t max)
 510 {
 511         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 512         struct disk_sm_root root_le;
 513
 514         root_le.nr_blocks = cpu_to_le64(smm->ll.nr_blocks);
 515         root_le.nr_allocated = cpu_to_le64(smm->ll.nr_allocated);
 516         root_le.bitmap_root = cpu_to_le64(smm->ll.bitmap_root);
 517         root_le.ref_count_root = cpu_to_le64(smm->ll.ref_count_root);
 518
 519         if (max < sizeof(root_le))
 520                 return -ENOSPC;
 521
 522         memcpy(where_le, &root_le, sizeof(root_le));
 523
 524         return 0;
 525 }
 526
 527 static int sm_metadata_extend(struct dm_space_map *sm, dm_block_t extra_blocks);
 528
 529 static struct dm_space_map ops = {
 530         .destroy = sm_metadata_destroy,
 531         .extend = sm_metadata_extend,
 532         .get_nr_blocks = sm_metadata_get_nr_blocks,
 533         .get_nr_free = sm_metadata_get_nr_free,
 534         .get_count = sm_metadata_get_count,
 535         .count_is_more_than_one = sm_metadata_count_is_more_than_one,
 536         .set_count = sm_metadata_set_count,
 537         .inc_block = sm_metadata_inc_block,
 538         .dec_block = sm_metadata_dec_block,
 539         .new_block = sm_metadata_new_block,
 540         .commit = sm_metadata_commit,
 541         .root_size = sm_metadata_root_size,
 542         .copy_root = sm_metadata_copy_root,
 543         .register_threshold_callback = sm_metadata_register_threshold_callback
 544 };
 545
 546 /*----------------------------------------------------------------*/
 547
 548 /*
 549  * When a new space map is created that manages its own space.  We use
 550  * this tiny bootstrap allocator.
 551  */
 552 static void sm_bootstrap_destroy(struct dm_space_map *sm)
 553 {
 554 }
 555
 556 static int sm_bootstrap_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
 557 {
 558         DMERR("bootstrap doesn't support extend");
 559
 560         return -EINVAL;
 561 }
 562
 563 static int sm_bootstrap_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
 564 {
 565         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 566
 567         return smm->ll.nr_blocks;
 568 }
 569
 570 static int sm_bootstrap_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
 571 {
 572         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 573
 574         *count = smm->ll.nr_blocks - smm->begin;
 575
 576         return 0;
 577 }
 578
 579 static int sm_bootstrap_get_count(struct dm_space_map *sm, dm_block_t b,
 580                                   uint32_t *result)
 581 {
 582         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 583
 584         return b < smm->begin ? 1 : 0;
 585 }
 586
 587 static int sm_bootstrap_count_is_more_than_one(struct dm_space_map *sm,
 588                                                dm_block_t b, int *result)
 589 {
 590         *result = 0;
 591
 592         return 0;
 593 }
 594
 595 static int sm_bootstrap_set_count(struct dm_space_map *sm, dm_block_t b,
 596                                   uint32_t count)
 597 {
 598         DMERR("bootstrap doesn't support set_count");
 599
 600         return -EINVAL;
 601 }
 602
 603 static int sm_bootstrap_new_block(struct dm_space_map *sm, dm_block_t *b)
 604 {
 605         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 606
 607         /*
 608          * We know the entire device is unused.
 609          */
 610         if (smm->begin == smm->ll.nr_blocks)
 611                 return -ENOSPC;
 612
 613         *b = smm->begin++;
 614
 615         return 0;
 616 }
 617
 618 static int sm_bootstrap_inc_block(struct dm_space_map *sm, dm_block_t b)
 619 {
 620         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 621
 622         return add_bop(smm, BOP_INC, b);
 623 }
 624
 625 static int sm_bootstrap_dec_block(struct dm_space_map *sm, dm_block_t b)
 626 {
 627         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 628
 629         return add_bop(smm, BOP_DEC, b);
 630 }
 631
 632 static int sm_bootstrap_commit(struct dm_space_map *sm)
 633 {
 634         return 0;
 635 }
 636
 637 static int sm_bootstrap_root_size(struct dm_space_map *sm, size_t *result)
 638 {
 639         DMERR("bootstrap doesn't support root_size");
 640
 641         return -EINVAL;
 642 }
 643
 644 static int sm_bootstrap_copy_root(struct dm_space_map *sm, void *where,
 645                                   size_t max)
 646 {
 647         DMERR("bootstrap doesn't support copy_root");
 648
 649         return -EINVAL;
 650 }
 651
 652 static struct dm_space_map bootstrap_ops = {
 653         .destroy = sm_bootstrap_destroy,
 654         .extend = sm_bootstrap_extend,
 655         .get_nr_blocks = sm_bootstrap_get_nr_blocks,
 656         .get_nr_free = sm_bootstrap_get_nr_free,
 657         .get_count = sm_bootstrap_get_count,
 658         .count_is_more_than_one = sm_bootstrap_count_is_more_than_one,
 659         .set_count = sm_bootstrap_set_count,
 660         .inc_block = sm_bootstrap_inc_block,
 661         .dec_block = sm_bootstrap_dec_block,
 662         .new_block = sm_bootstrap_new_block,
 663         .commit = sm_bootstrap_commit,
 664         .root_size = sm_bootstrap_root_size,
 665         .copy_root = sm_bootstrap_copy_root,
 666         .register_threshold_callback = NULL
 667 };
 668
 669 /*----------------------------------------------------------------*/
 670
 671 static int sm_metadata_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
 672 {
 673         int r, i;
 674         enum allocation_event ev;
 675         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 676         dm_block_t old_len = smm->ll.nr_blocks;
 677
 678         /*
 679          * Flick into a mode where all blocks get allocated in the new area.
 680          */
 681         smm->begin = old_len;
 682         memcpy(sm, &bootstrap_ops, sizeof(*sm));
 683
 684         /*
 685          * Extend.
 686          */
 687         r = sm_ll_extend(&smm->ll, extra_blocks);
 688         if (r)
 689                 goto out;
 690
 691         /*
 692          * We repeatedly increment then commit until the commit doesn't
 693          * allocate any new blocks.
 694          */
 695         do {
 696                 for (i = old_len; !r && i < smm->begin; i++) {
 697                         r = sm_ll_inc(&smm->ll, i, &ev);
 698                         if (r)
 699                                 goto out;
 700                 }
 701                 old_len = smm->begin;
 702
 703                 r = sm_ll_commit(&smm->ll);
 704                 if (r)
 705                         goto out;
 706
 707         } while (old_len != smm->begin);
 708
 709 out:
 710         /*
 711          * Switch back to normal behaviour.
 712          */
 713         memcpy(sm, &ops, sizeof(*sm));
 714         return r;
 715 }
 716
 717 /*----------------------------------------------------------------*/
 718
 719 struct dm_space_map *dm_sm_metadata_init(void)
 720 {
 721         struct sm_metadata *smm;
 722
 723         smm = kmalloc(sizeof(*smm), GFP_KERNEL);
 724         if (!smm)
 725                 return ERR_PTR(-ENOMEM);
 726
 727         memcpy(&smm->sm, &ops, sizeof(smm->sm));
 728
 729         return &smm->sm;
 730 }
 731
 732 int dm_sm_metadata_create(struct dm_space_map *sm,
 733                           struct dm_transaction_manager *tm,
 734                           dm_block_t nr_blocks,
 735                           dm_block_t superblock)
 736 {
 737         int r;
 738         dm_block_t i;
 739         enum allocation_event ev;
 740         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 741
 742         smm->begin = superblock + 1;
 743         smm->recursion_count = 0;
 744         smm->allocated_this_transaction = 0;
 745         brb_init(&smm->uncommitted);
 746         threshold_init(&smm->threshold);
 747
 748         memcpy(&smm->sm, &bootstrap_ops, sizeof(smm->sm));
 749
 750         r = sm_ll_new_metadata(&smm->ll, tm);
 751         if (r)
 752                 return r;
 753
 754         r = sm_ll_extend(&smm->ll, nr_blocks);
 755         if (r)
 756                 return r;
 757
 758         memcpy(&smm->sm, &ops, sizeof(smm->sm));
 759
 760         /*
 761          * Now we need to update the newly created data structures with the
 762          * allocated blocks that they were built from.
 763          */
 764         for (i = superblock; !r && i < smm->begin; i++)
 765                 r = sm_ll_inc(&smm->ll, i, &ev);
 766
 767         if (r)
 768                 return r;
 769
 770         return sm_metadata_commit(sm);
 771 }
 772
 773 int dm_sm_metadata_open(struct dm_space_map *sm,
 774                         struct dm_transaction_manager *tm,
 775                         void *root_le, size_t len)
 776 {
 777         int r;
 778         struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
 779
 780         r = sm_ll_open_metadata(&smm->ll, tm, root_le, len);
 781         if (r)
 782                 return r;
 783
 784         smm->begin = 0;
 785         smm->recursion_count = 0;
 786         smm->allocated_this_transaction = 0;
 787         brb_init(&smm->uncommitted);
 788         threshold_init(&smm->threshold);
 789
 790         memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
 791         return 0;
 792 }