module/zfs/space_map.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25 /*
  26  * Copyright (c) 2012 by Delphix. All rights reserved.
  27  */
  28
  29 #include <sys/zfs_context.h>
  30 #include <sys/spa.h>
  31 #include <sys/dmu.h>
  32 #include <sys/zio.h>
  33 #include <sys/space_map.h>
  34
  35 static kmem_cache_t *space_seg_cache;
  36
  37 void
  38 space_map_init(void)
  39 {
  40         ASSERT(space_seg_cache == NULL);
  41         space_seg_cache = kmem_cache_create("space_seg_cache",
  42             sizeof (space_seg_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
  43 }
  44
  45 void
  46 space_map_fini(void)
  47 {
  48         kmem_cache_destroy(space_seg_cache);
  49         space_seg_cache = NULL;
  50 }
  51
  52 /*
  53  * Space map routines.
  54  * NOTE: caller is responsible for all locking.
  55  */
  56 static int
  57 space_map_seg_compare(const void *x1, const void *x2)
  58 {
  59         const space_seg_t *s1 = x1;
  60         const space_seg_t *s2 = x2;
  61
  62         if (s1->ss_start < s2->ss_start) {
  63                 if (s1->ss_end > s2->ss_start)
  64                         return (0);
  65                 return (-1);
  66         }
  67         if (s1->ss_start > s2->ss_start) {
  68                 if (s1->ss_start < s2->ss_end)
  69                         return (0);
  70                 return (1);
  71         }
  72         return (0);
  73 }
  74
  75 void
  76 space_map_create(space_map_t *sm, uint64_t start, uint64_t size, uint8_t shift,
  77         kmutex_t *lp)
  78 {
  79         bzero(sm, sizeof (*sm));
  80
  81         cv_init(&sm->sm_load_cv, NULL, CV_DEFAULT, NULL);
  82
  83         avl_create(&sm->sm_root, space_map_seg_compare,
  84             sizeof (space_seg_t), offsetof(struct space_seg, ss_node));
  85
  86         sm->sm_start = start;
  87         sm->sm_size = size;
  88         sm->sm_shift = shift;
  89         sm->sm_lock = lp;
  90 }
  91
  92 void
  93 space_map_destroy(space_map_t *sm)
  94 {
  95         ASSERT(!sm->sm_loaded && !sm->sm_loading);
  96         VERIFY0(sm->sm_space);
  97         avl_destroy(&sm->sm_root);
  98         cv_destroy(&sm->sm_load_cv);
  99 }
 100
 101 void
 102 space_map_add(space_map_t *sm, uint64_t start, uint64_t size)
 103 {
 104         avl_index_t where;
 105         space_seg_t ssearch, *ss_before, *ss_after, *ss;
 106         uint64_t end = start + size;
 107         int merge_before, merge_after;
 108
 109         ASSERT(MUTEX_HELD(sm->sm_lock));
 110         VERIFY(size != 0);
 111         VERIFY3U(start, >=, sm->sm_start);
 112         VERIFY3U(end, <=, sm->sm_start + sm->sm_size);
 113         VERIFY(sm->sm_space + size <= sm->sm_size);
 114         VERIFY(P2PHASE(start, 1ULL << sm->sm_shift) == 0);
 115         VERIFY(P2PHASE(size, 1ULL << sm->sm_shift) == 0);
 116
 117         ssearch.ss_start = start;
 118         ssearch.ss_end = end;
 119         ss = avl_find(&sm->sm_root, &ssearch, &where);
 120
 121         if (ss != NULL && ss->ss_start <= start && ss->ss_end >= end) {
 122                 zfs_panic_recover("zfs: allocating allocated segment"
 123                     "(offset=%llu size=%llu)\n",
 124                     (longlong_t)start, (longlong_t)size);
 125                 return;
 126         }
 127
 128         /* Make sure we don't overlap with either of our neighbors */
 129         VERIFY(ss == NULL);
 130
 131         ss_before = avl_nearest(&sm->sm_root, where, AVL_BEFORE);
 132         ss_after = avl_nearest(&sm->sm_root, where, AVL_AFTER);
 133
 134         merge_before = (ss_before != NULL && ss_before->ss_end == start);
 135         merge_after = (ss_after != NULL && ss_after->ss_start == end);
 136
 137         if (merge_before && merge_after) {
 138                 avl_remove(&sm->sm_root, ss_before);
 139                 if (sm->sm_pp_root) {
 140                         avl_remove(sm->sm_pp_root, ss_before);
 141                         avl_remove(sm->sm_pp_root, ss_after);
 142                 }
 143                 ss_after->ss_start = ss_before->ss_start;
 144                 kmem_cache_free(space_seg_cache, ss_before);
 145                 ss = ss_after;
 146         } else if (merge_before) {
 147                 ss_before->ss_end = end;
 148                 if (sm->sm_pp_root)
 149                         avl_remove(sm->sm_pp_root, ss_before);
 150                 ss = ss_before;
 151         } else if (merge_after) {
 152                 ss_after->ss_start = start;
 153                 if (sm->sm_pp_root)
 154                         avl_remove(sm->sm_pp_root, ss_after);
 155                 ss = ss_after;
 156         } else {
 157                 ss = kmem_cache_alloc(space_seg_cache, KM_PUSHPAGE);
 158                 ss->ss_start = start;
 159                 ss->ss_end = end;
 160                 avl_insert(&sm->sm_root, ss, where);
 161         }
 162
 163         if (sm->sm_pp_root)
 164                 avl_add(sm->sm_pp_root, ss);
 165
 166         sm->sm_space += size;
 167 }
 168
 169 void
 170 space_map_remove(space_map_t *sm, uint64_t start, uint64_t size)
 171 {
 172         avl_index_t where;
 173         space_seg_t ssearch, *ss, *newseg;
 174         uint64_t end = start + size;
 175         int left_over, right_over;
 176
 177         ASSERT(MUTEX_HELD(sm->sm_lock));
 178         VERIFY(size != 0);
 179         VERIFY(P2PHASE(start, 1ULL << sm->sm_shift) == 0);
 180         VERIFY(P2PHASE(size, 1ULL << sm->sm_shift) == 0);
 181
 182         ssearch.ss_start = start;
 183         ssearch.ss_end = end;
 184         ss = avl_find(&sm->sm_root, &ssearch, &where);
 185
 186         /* Make sure we completely overlap with someone */
 187         if (ss == NULL) {
 188                 zfs_panic_recover("zfs: freeing free segment "
 189                     "(offset=%llu size=%llu)",
 190                     (longlong_t)start, (longlong_t)size);
 191                 return;
 192         }
 193         VERIFY3U(ss->ss_start, <=, start);
 194         VERIFY3U(ss->ss_end, >=, end);
 195         VERIFY(sm->sm_space - size <= sm->sm_size);
 196
 197         left_over = (ss->ss_start != start);
 198         right_over = (ss->ss_end != end);
 199
 200         if (sm->sm_pp_root)
 201                 avl_remove(sm->sm_pp_root, ss);
 202
 203         if (left_over && right_over) {
 204                 newseg = kmem_cache_alloc(space_seg_cache, KM_PUSHPAGE);
 205                 newseg->ss_start = end;
 206                 newseg->ss_end = ss->ss_end;
 207                 ss->ss_end = start;
 208                 avl_insert_here(&sm->sm_root, newseg, ss, AVL_AFTER);
 209                 if (sm->sm_pp_root)
 210                         avl_add(sm->sm_pp_root, newseg);
 211         } else if (left_over) {
 212                 ss->ss_end = start;
 213         } else if (right_over) {
 214                 ss->ss_start = end;
 215         } else {
 216                 avl_remove(&sm->sm_root, ss);
 217                 kmem_cache_free(space_seg_cache, ss);
 218                 ss = NULL;
 219         }
 220
 221         if (sm->sm_pp_root && ss != NULL)
 222                 avl_add(sm->sm_pp_root, ss);
 223
 224         sm->sm_space -= size;
 225 }
 226
 227 boolean_t
 228 space_map_contains(space_map_t *sm, uint64_t start, uint64_t size)
 229 {
 230         avl_index_t where;
 231         space_seg_t ssearch, *ss;
 232         uint64_t end = start + size;
 233
 234         ASSERT(MUTEX_HELD(sm->sm_lock));
 235         VERIFY(size != 0);
 236         VERIFY(P2PHASE(start, 1ULL << sm->sm_shift) == 0);
 237         VERIFY(P2PHASE(size, 1ULL << sm->sm_shift) == 0);
 238
 239         ssearch.ss_start = start;
 240         ssearch.ss_end = end;
 241         ss = avl_find(&sm->sm_root, &ssearch, &where);
 242
 243         return (ss != NULL && ss->ss_start <= start && ss->ss_end >= end);
 244 }
 245
 246 void
 247 space_map_vacate(space_map_t *sm, space_map_func_t *func, space_map_t *mdest)
 248 {
 249         space_seg_t *ss;
 250         void *cookie = NULL;
 251
 252         ASSERT(MUTEX_HELD(sm->sm_lock));
 253
 254         while ((ss = avl_destroy_nodes(&sm->sm_root, &cookie)) != NULL) {
 255                 if (func != NULL)
 256                         func(mdest, ss->ss_start, ss->ss_end - ss->ss_start);
 257                 kmem_cache_free(space_seg_cache, ss);
 258         }
 259         sm->sm_space = 0;
 260 }
 261
 262 void
 263 space_map_walk(space_map_t *sm, space_map_func_t *func, space_map_t *mdest)
 264 {
 265         space_seg_t *ss;
 266
 267         ASSERT(MUTEX_HELD(sm->sm_lock));
 268
 269         for (ss = avl_first(&sm->sm_root); ss; ss = AVL_NEXT(&sm->sm_root, ss))
 270                 func(mdest, ss->ss_start, ss->ss_end - ss->ss_start);
 271 }
 272
 273 /*
 274  * Wait for any in-progress space_map_load() to complete.
 275  */
 276 void
 277 space_map_load_wait(space_map_t *sm)
 278 {
 279         ASSERT(MUTEX_HELD(sm->sm_lock));
 280
 281         while (sm->sm_loading) {
 282                 ASSERT(!sm->sm_loaded);
 283                 cv_wait(&sm->sm_load_cv, sm->sm_lock);
 284         }
 285 }
 286
 287 /*
 288  * Note: space_map_load() will drop sm_lock across dmu_read() calls.
 289  * The caller must be OK with this.
 290  */
 291 int
 292 space_map_load(space_map_t *sm, space_map_ops_t *ops, uint8_t maptype,
 293         space_map_obj_t *smo, objset_t *os)
 294 {
 295         uint64_t *entry, *entry_map, *entry_map_end;
 296         uint64_t bufsize, size, offset, end, space;
 297         uint64_t mapstart = sm->sm_start;
 298         int error = 0;
 299
 300         ASSERT(MUTEX_HELD(sm->sm_lock));
 301         ASSERT(!sm->sm_loaded);
 302         ASSERT(!sm->sm_loading);
 303
 304         sm->sm_loading = B_TRUE;
 305         end = smo->smo_objsize;
 306         space = smo->smo_alloc;
 307
 308         ASSERT(sm->sm_ops == NULL);
 309         VERIFY0(sm->sm_space);
 310
 311         if (maptype == SM_FREE) {
 312                 space_map_add(sm, sm->sm_start, sm->sm_size);
 313                 space = sm->sm_size - space;
 314         }
 315
 316         bufsize = 1ULL << SPACE_MAP_BLOCKSHIFT;
 317         entry_map = zio_buf_alloc(bufsize);
 318
 319         mutex_exit(sm->sm_lock);
 320         if (end > bufsize)
 321                 dmu_prefetch(os, smo->smo_object, bufsize, end - bufsize);
 322         mutex_enter(sm->sm_lock);
 323
 324         for (offset = 0; offset < end; offset += bufsize) {
 325                 size = MIN(end - offset, bufsize);
 326                 VERIFY(P2PHASE(size, sizeof (uint64_t)) == 0);
 327                 VERIFY(size != 0);
 328
 329                 dprintf("object=%llu  offset=%llx  size=%llx\n",
 330                     smo->smo_object, offset, size);
 331
 332                 mutex_exit(sm->sm_lock);
 333                 error = dmu_read(os, smo->smo_object, offset, size, entry_map,
 334                     DMU_READ_PREFETCH);
 335                 mutex_enter(sm->sm_lock);
 336                 if (error != 0)
 337                         break;
 338
 339                 entry_map_end = entry_map + (size / sizeof (uint64_t));
 340                 for (entry = entry_map; entry < entry_map_end; entry++) {
 341                         uint64_t e = *entry;
 342
 343                         if (SM_DEBUG_DECODE(e))         /* Skip debug entries */
 344                                 continue;
 345
 346                         (SM_TYPE_DECODE(e) == maptype ?
 347                             space_map_add : space_map_remove)(sm,
 348                             (SM_OFFSET_DECODE(e) << sm->sm_shift) + mapstart,
 349                             SM_RUN_DECODE(e) << sm->sm_shift);
 350                 }
 351         }
 352
 353         if (error == 0) {
 354                 VERIFY3U(sm->sm_space, ==, space);
 355
 356                 sm->sm_loaded = B_TRUE;
 357                 sm->sm_ops = ops;
 358                 if (ops != NULL)
 359                         ops->smop_load(sm);
 360         } else {
 361                 space_map_vacate(sm, NULL, NULL);
 362         }
 363
 364         zio_buf_free(entry_map, bufsize);
 365
 366         sm->sm_loading = B_FALSE;
 367
 368         cv_broadcast(&sm->sm_load_cv);
 369
 370         return (error);
 371 }
 372
 373 void
 374 space_map_unload(space_map_t *sm)
 375 {
 376         ASSERT(MUTEX_HELD(sm->sm_lock));
 377
 378         if (sm->sm_loaded && sm->sm_ops != NULL)
 379                 sm->sm_ops->smop_unload(sm);
 380
 381         sm->sm_loaded = B_FALSE;
 382         sm->sm_ops = NULL;
 383
 384         space_map_vacate(sm, NULL, NULL);
 385 }
 386
 387 uint64_t
 388 space_map_maxsize(space_map_t *sm)
 389 {
 390         ASSERT(sm->sm_ops != NULL);
 391         return (sm->sm_ops->smop_max(sm));
 392 }
 393
 394 uint64_t
 395 space_map_alloc(space_map_t *sm, uint64_t size)
 396 {
 397         uint64_t start;
 398
 399         start = sm->sm_ops->smop_alloc(sm, size);
 400         if (start != -1ULL)
 401                 space_map_remove(sm, start, size);
 402         return (start);
 403 }
 404
 405 void
 406 space_map_claim(space_map_t *sm, uint64_t start, uint64_t size)
 407 {
 408         sm->sm_ops->smop_claim(sm, start, size);
 409         space_map_remove(sm, start, size);
 410 }
 411
 412 void
 413 space_map_free(space_map_t *sm, uint64_t start, uint64_t size)
 414 {
 415         space_map_add(sm, start, size);
 416         sm->sm_ops->smop_free(sm, start, size);
 417 }
 418
 419 /*
 420  * Note: space_map_sync() will drop sm_lock across dmu_write() calls.
 421  */
 422 void
 423 space_map_sync(space_map_t *sm, uint8_t maptype,
 424         space_map_obj_t *smo, objset_t *os, dmu_tx_t *tx)
 425 {
 426         spa_t *spa = dmu_objset_spa(os);
 427         void *cookie = NULL;
 428         space_seg_t *ss;
 429         uint64_t bufsize, start, size, run_len, delta, sm_space;
 430         uint64_t *entry, *entry_map, *entry_map_end;
 431
 432         ASSERT(MUTEX_HELD(sm->sm_lock));
 433
 434         if (sm->sm_space == 0)
 435                 return;
 436
 437         dprintf("object %4llu, txg %llu, pass %d, %c, count %lu, space %llx\n",
 438             smo->smo_object, dmu_tx_get_txg(tx), spa_sync_pass(spa),
 439             maptype == SM_ALLOC ? 'A' : 'F', avl_numnodes(&sm->sm_root),
 440             sm->sm_space);
 441
 442         if (maptype == SM_ALLOC)
 443                 smo->smo_alloc += sm->sm_space;
 444         else
 445                 smo->smo_alloc -= sm->sm_space;
 446
 447         bufsize = (8 + avl_numnodes(&sm->sm_root)) * sizeof (uint64_t);
 448         bufsize = MIN(bufsize, 1ULL << SPACE_MAP_BLOCKSHIFT);
 449         entry_map = zio_buf_alloc(bufsize);
 450         entry_map_end = entry_map + (bufsize / sizeof (uint64_t));
 451         entry = entry_map;
 452
 453         *entry++ = SM_DEBUG_ENCODE(1) |
 454             SM_DEBUG_ACTION_ENCODE(maptype) |
 455             SM_DEBUG_SYNCPASS_ENCODE(spa_sync_pass(spa)) |
 456             SM_DEBUG_TXG_ENCODE(dmu_tx_get_txg(tx));
 457
 458         delta = 0;
 459         sm_space = sm->sm_space;
 460         while ((ss = avl_destroy_nodes(&sm->sm_root, &cookie)) != NULL) {
 461                 size = ss->ss_end - ss->ss_start;
 462                 start = (ss->ss_start - sm->sm_start) >> sm->sm_shift;
 463
 464                 delta += size;
 465                 size >>= sm->sm_shift;
 466
 467                 while (size) {
 468                         run_len = MIN(size, SM_RUN_MAX);
 469
 470                         if (entry == entry_map_end) {
 471                                 mutex_exit(sm->sm_lock);
 472                                 dmu_write(os, smo->smo_object, smo->smo_objsize,
 473                                     bufsize, entry_map, tx);
 474                                 mutex_enter(sm->sm_lock);
 475                                 smo->smo_objsize += bufsize;
 476                                 entry = entry_map;
 477                         }
 478
 479                         *entry++ = SM_OFFSET_ENCODE(start) |
 480                             SM_TYPE_ENCODE(maptype) |
 481                             SM_RUN_ENCODE(run_len);
 482
 483                         start += run_len;
 484                         size -= run_len;
 485                 }
 486                 kmem_cache_free(space_seg_cache, ss);
 487         }
 488
 489         if (entry != entry_map) {
 490                 size = (entry - entry_map) * sizeof (uint64_t);
 491                 mutex_exit(sm->sm_lock);
 492                 dmu_write(os, smo->smo_object, smo->smo_objsize,
 493                     size, entry_map, tx);
 494                 mutex_enter(sm->sm_lock);
 495                 smo->smo_objsize += size;
 496         }
 497
 498         /*
 499          * Ensure that the space_map's accounting wasn't changed
 500          * while we were in the middle of writing it out.
 501          */
 502         VERIFY3U(sm->sm_space, ==, sm_space);
 503
 504         zio_buf_free(entry_map, bufsize);
 505
 506         sm->sm_space -= delta;
 507         VERIFY0(sm->sm_space);
 508 }
 509
 510 void
 511 space_map_truncate(space_map_obj_t *smo, objset_t *os, dmu_tx_t *tx)
 512 {
 513         VERIFY(dmu_free_range(os, smo->smo_object, 0, -1ULL, tx) == 0);
 514
 515         smo->smo_objsize = 0;
 516         smo->smo_alloc = 0;
 517 }
 518
 519 /*
 520  * Space map reference trees.
 521  *
 522  * A space map is a collection of integers.  Every integer is either
 523  * in the map, or it's not.  A space map reference tree generalizes
 524  * the idea: it allows its members to have arbitrary reference counts,
 525  * as opposed to the implicit reference count of 0 or 1 in a space map.
 526  * This representation comes in handy when computing the union or
 527  * intersection of multiple space maps.  For example, the union of
 528  * N space maps is the subset of the reference tree with refcnt >= 1.
 529  * The intersection of N space maps is the subset with refcnt >= N.
 530  *
 531  * [It's very much like a Fourier transform.  Unions and intersections
 532  * are hard to perform in the 'space map domain', so we convert the maps
 533  * into the 'reference count domain', where it's trivial, then invert.]
 534  *
 535  * vdev_dtl_reassess() uses computations of this form to determine
 536  * DTL_MISSING and DTL_OUTAGE for interior vdevs -- e.g. a RAID-Z vdev
 537  * has an outage wherever refcnt >= vdev_nparity + 1, and a mirror vdev
 538  * has an outage wherever refcnt >= vdev_children.
 539  */
 540 static int
 541 space_map_ref_compare(const void *x1, const void *x2)
 542 {
 543         const space_ref_t *sr1 = x1;
 544         const space_ref_t *sr2 = x2;
 545
 546         if (sr1->sr_offset < sr2->sr_offset)
 547                 return (-1);
 548         if (sr1->sr_offset > sr2->sr_offset)
 549                 return (1);
 550
 551         if (sr1 < sr2)
 552                 return (-1);
 553         if (sr1 > sr2)
 554                 return (1);
 555
 556         return (0);
 557 }
 558
 559 void
 560 space_map_ref_create(avl_tree_t *t)
 561 {
 562         avl_create(t, space_map_ref_compare,
 563             sizeof (space_ref_t), offsetof(space_ref_t, sr_node));
 564 }
 565
 566 void
 567 space_map_ref_destroy(avl_tree_t *t)
 568 {
 569         space_ref_t *sr;
 570         void *cookie = NULL;
 571
 572         while ((sr = avl_destroy_nodes(t, &cookie)) != NULL)
 573                 kmem_free(sr, sizeof (*sr));
 574
 575         avl_destroy(t);
 576 }
 577
 578 static void
 579 space_map_ref_add_node(avl_tree_t *t, uint64_t offset, int64_t refcnt)
 580 {
 581         space_ref_t *sr;
 582
 583         sr = kmem_alloc(sizeof (*sr), KM_PUSHPAGE);
 584         sr->sr_offset = offset;
 585         sr->sr_refcnt = refcnt;
 586
 587         avl_add(t, sr);
 588 }
 589
 590 void
 591 space_map_ref_add_seg(avl_tree_t *t, uint64_t start, uint64_t end,
 592         int64_t refcnt)
 593 {
 594         space_map_ref_add_node(t, start, refcnt);
 595         space_map_ref_add_node(t, end, -refcnt);
 596 }
 597
 598 /*
 599  * Convert (or add) a space map into a reference tree.
 600  */
 601 void
 602 space_map_ref_add_map(avl_tree_t *t, space_map_t *sm, int64_t refcnt)
 603 {
 604         space_seg_t *ss;
 605
 606         ASSERT(MUTEX_HELD(sm->sm_lock));
 607
 608         for (ss = avl_first(&sm->sm_root); ss; ss = AVL_NEXT(&sm->sm_root, ss))
 609                 space_map_ref_add_seg(t, ss->ss_start, ss->ss_end, refcnt);
 610 }
 611
 612 /*
 613  * Convert a reference tree into a space map.  The space map will contain
 614  * all members of the reference tree for which refcnt >= minref.
 615  */
 616 void
 617 space_map_ref_generate_map(avl_tree_t *t, space_map_t *sm, int64_t minref)
 618 {
 619         uint64_t start = -1ULL;
 620         int64_t refcnt = 0;
 621         space_ref_t *sr;
 622
 623         ASSERT(MUTEX_HELD(sm->sm_lock));
 624
 625         space_map_vacate(sm, NULL, NULL);
 626
 627         for (sr = avl_first(t); sr != NULL; sr = AVL_NEXT(t, sr)) {
 628                 refcnt += sr->sr_refcnt;
 629                 if (refcnt >= minref) {
 630                         if (start == -1ULL) {
 631                                 start = sr->sr_offset;
 632                         }
 633                 } else {
 634                         if (start != -1ULL) {
 635                                 uint64_t end = sr->sr_offset;
 636                                 ASSERT(start <= end);
 637                                 if (end > start)
 638                                         space_map_add(sm, start, end - start);
 639                                 start = -1ULL;
 640                         }
 641                 }
 642         }
 643         ASSERT(refcnt == 0);
 644         ASSERT(start == -1ULL);
 645 }