sys/vfs/hammer/hammer_rebalance.c

   1 /*
   2  * Copyright (c) 2009 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include "hammer.h"
  36
  37 static int rebalance_node(struct hammer_ioc_rebalance *rebal,
  38                         hammer_cursor_t cursor, hammer_node_lock_t lcache);
  39 static void rebalance_closeout(hammer_node_lock_t base_item, int base_count,
  40                         hammer_btree_elm_t elm);
  41 static void rebalance_parent_ptrs(hammer_node_lock_t base_item, int index,
  42                         hammer_node_lock_t item, hammer_node_lock_t chld_item);
  43
  44 /*
  45  * Iterate through the specified range of object ids and rebalance B-Tree
  46  * leaf and internal nodes we encounter.  A forwards iteration is used.
  47  *
  48  * All leafs are at the same depth.  We use the b-tree scan code loosely
  49  * to position ourselves and create degenerate cases to skip indices
  50  * that we have rebalanced in bulk.
  51  */
  52
  53 int
  54 hammer_ioc_rebalance(hammer_transaction_t trans, hammer_inode_t ip,
  55                  struct hammer_ioc_rebalance *rebal)
  56 {
  57         struct hammer_cursor cursor;
  58         struct hammer_node_lock lcache;
  59         hammer_btree_leaf_elm_t elm;
  60         int error;
  61         int seq;
  62         uint32_t key_end_localization;
  63
  64         if ((rebal->key_beg.localization | rebal->key_end.localization) &
  65             HAMMER_LOCALIZE_PSEUDOFS_MASK) {
  66                 return(EINVAL);
  67         }
  68         if (rebal->key_beg.localization > rebal->key_end.localization)
  69                 return(EINVAL);
  70         if (rebal->key_beg.localization == rebal->key_end.localization) {
  71                 if (rebal->key_beg.obj_id > rebal->key_end.obj_id)
  72                         return(EINVAL);
  73                 /* key-space limitations - no check needed */
  74         }
  75         if (rebal->saturation < HAMMER_BTREE_INT_ELMS / 2)
  76                 rebal->saturation = HAMMER_BTREE_INT_ELMS / 2;
  77         if (rebal->saturation > HAMMER_BTREE_INT_ELMS)
  78                 rebal->saturation = HAMMER_BTREE_INT_ELMS;
  79
  80         /*
  81          * Ioctl caller has only set localization type to rebalance.
  82          * Initialize cursor key localization with ip localization.
  83          */
  84         rebal->key_cur = rebal->key_beg;
  85         rebal->key_cur.localization &= HAMMER_LOCALIZE_MASK;
  86         if (rebal->allpfs == 0)
  87                 rebal->key_cur.localization |= ip->obj_localization;
  88
  89         key_end_localization = rebal->key_end.localization;
  90         key_end_localization &= HAMMER_LOCALIZE_MASK;
  91         if (rebal->allpfs == 0)
  92                 key_end_localization |= ip->obj_localization;
  93         else
  94                 key_end_localization |= pfs_to_lo(HAMMER_MAX_PFSID);
  95
  96         hammer_btree_lcache_init(trans->hmp, &lcache, 2);
  97
  98         seq = trans->hmp->flusher.done;
  99
 100         /*
 101          * Scan forwards.  Retries typically occur if a deadlock is detected.
 102          */
 103 retry:
 104         error = hammer_init_cursor(trans, &cursor, NULL, NULL);
 105         if (error) {
 106                 hammer_done_cursor(&cursor);
 107                 goto failed;
 108         }
 109         cursor.key_beg = rebal->key_cur;
 110         cursor.key_end = rebal->key_end;
 111         cursor.key_end.localization = key_end_localization;
 112         cursor.flags |= HAMMER_CURSOR_END_INCLUSIVE;
 113         cursor.flags |= HAMMER_CURSOR_BACKEND;
 114
 115         /*
 116          * Cause internal nodes to be returned on the way up.  Internal nodes
 117          * are not returned on the way down so we can create a degenerate
 118          * case to handle internal nodes as a trailing function of their
 119          * sub-trees.
 120          *
 121          * Note that by not setting INSERTING or PRUNING no boundary
 122          * corrections will be made and a sync lock is not needed for the
 123          * B-Tree scan itself.
 124          */
 125         cursor.flags |= HAMMER_CURSOR_REBLOCKING;
 126
 127         error = hammer_btree_first(&cursor);
 128
 129         while (error == 0) {
 130                 /*
 131                  * Rebalancing can be hard on the memory allocator, make
 132                  * sure there is enough free memory before doing it.
 133                  */
 134                 if (vm_test_nominal()) {
 135                         hammer_unlock_cursor(&cursor);
 136                         vm_wait_nominal();
 137                         hammer_lock_cursor(&cursor);
 138                 }
 139
 140                 /*
 141                  * We only care about internal nodes visited for the last
 142                  * time on the way up... that is, a trailing scan of the
 143                  * internal node after all of its children have been recursed
 144                  * through.
 145                  */
 146                 if (cursor.node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL) {
 147                         /*
 148                          * Leave cursor.index alone, we want to recurse
 149                          * through all children of the internal node before
 150                          * visiting it.
 151                          *
 152                          * Process the internal node on the way up after
 153                          * the last child's sub-tree has been balanced.
 154                          */
 155                         if (cursor.index == cursor.node->ondisk->count - 1) {
 156                                 hammer_sync_lock_sh(trans);
 157                                 error = rebalance_node(rebal, &cursor, &lcache);
 158                                 hammer_sync_unlock(trans);
 159                         }
 160                 } else {
 161                         /*
 162                          * We don't need to iterate through all the leaf
 163                          * elements, we only care about the parent (internal)
 164                          * node.
 165                          */
 166                         cursor.index = cursor.node->ondisk->count - 1;
 167                 }
 168                 if (error)
 169                         break;
 170
 171                 /*
 172                  * Update returned scan position and do a flush if
 173                  * necessary.
 174                  *
 175                  * WARNING: We extract the base using the leaf element
 176                  *          type but this could be an internal node.  The
 177                  *          base is the same either way.
 178                  *
 179                  *          However, due to the rebalancing operation the
 180                  *          cursor position may have exceeded the right-hand
 181                  *          boundary.
 182                  *
 183                  * WARNING: See warnings in hammer_unlock_cursor()
 184                  *          function.
 185                  */
 186                 elm = &cursor.node->ondisk->elms[cursor.index].leaf;
 187                 rebal->key_cur = elm->base;
 188                 ++rebal->stat_ncount;
 189
 190                 while (hammer_flusher_meta_halflimit(trans->hmp) ||
 191                        hammer_flusher_undo_exhausted(trans, 2)) {
 192                         hammer_unlock_cursor(&cursor);
 193                         hammer_flusher_wait(trans->hmp, seq);
 194                         hammer_lock_cursor(&cursor);
 195                         seq = hammer_flusher_async_one(trans->hmp);
 196                 }
 197
 198                 /*
 199                  * Before iterating check if the rebalance operation caused
 200                  * the cursor to index past the right-hand boundary and make
 201                  * sure to stop if it does.  Otherwise the iteration may
 202                  * panic e.g. due to the key maxing out its fields and no
 203                  * longer being within the strict bounds of the root node.
 204                  */
 205                 if (hammer_btree_cmp(&rebal->key_cur, &cursor.key_end) > 0) {
 206                         rebal->key_cur = cursor.key_end;
 207                         break;
 208                 }
 209
 210                 /*
 211                  * Iterate, stop if a signal was received.
 212                  */
 213                 if ((error = hammer_signal_check(trans->hmp)) != 0)
 214                         break;
 215                 error = hammer_btree_iterate(&cursor);
 216         }
 217         if (error == ENOENT)
 218                 error = 0;
 219         hammer_done_cursor(&cursor);
 220         if (error == EDEADLK) {
 221                 ++rebal->stat_collisions;
 222                 goto retry;
 223         }
 224         if (error == EINTR) {
 225                 rebal->head.flags |= HAMMER_IOC_HEAD_INTR;
 226                 error = 0;
 227         }
 228 failed:
 229         rebal->key_cur.localization &= HAMMER_LOCALIZE_MASK;
 230         hammer_btree_lcache_free(trans->hmp, &lcache);
 231         return(error);
 232 }
 233
 234 /*
 235  * Rebalance an internal node, called via a trailing upward recursion.
 236  * All the children have already been individually rebalanced.
 237  *
 238  * To rebalance we scan the elements in the children and pack them,
 239  * so we actually need to lock the children and the children's children.
 240  *
 241  *      INTERNAL_NODE
 242  *      / / | | | \ \
 243  *     C C  C C C  C C  children (first level) (internal or leaf nodes)
 244  *                      children's elements (second level)
 245  *
 246  *      <<<----------   pack children's elements, possibly remove excess
 247  *                      children after packing.
 248  *
 249  * NOTE: The mirror_tids, parent pointers, and child pointers must be updated.
 250  *       Any live tracked B-Tree nodes must be updated (we worm out of that
 251  *       by not allowing any).  And boundary elements must be preserved.
 252  *
 253  * NOTE: If the children are leaf nodes we may have a degenerate case
 254  *       case where there are no elements in the leafs.
 255  *
 256  * XXX live-tracked
 257  */
 258 static int
 259 rebalance_node(struct hammer_ioc_rebalance *rebal, hammer_cursor_t cursor,
 260                hammer_node_lock_t lcache)
 261 {
 262         struct hammer_node_lock lockroot;
 263         hammer_node_lock_t base_item;
 264         hammer_node_lock_t chld_item;
 265         hammer_node_lock_t item;
 266         hammer_btree_elm_t elm;
 267         hammer_node_t node;
 268         hammer_tid_t tid;
 269         uint8_t type1 __debugvar;
 270         int base_count;
 271         int root_count;
 272         int avg_elms;
 273         int count;
 274         int error;
 275         int i;
 276         int n;
 277
 278         /*
 279          * Lock the parent node via the cursor, collect and lock our
 280          * children and children's children.
 281          *
 282          * By the way, this is a LOT of locks.
 283          */
 284         hammer_node_lock_init(&lockroot, cursor->node);
 285         error = hammer_cursor_upgrade(cursor);
 286         if (error)
 287                 goto done;
 288         error = hammer_btree_lock_children(cursor, 2, &lockroot, lcache);
 289         if (error)
 290                 goto done;
 291
 292         /*
 293          * Make a copy of all the locked on-disk data to simplify the element
 294          * shifting we are going to have to do.  We will modify the copy
 295          * first.
 296          */
 297         hammer_btree_lock_copy(cursor, &lockroot);
 298
 299         /*
 300          * Look at the first child node.
 301          */
 302         if (TAILQ_FIRST(&lockroot.list) == NULL)
 303                 goto done;
 304         type1 = TAILQ_FIRST(&lockroot.list)->node->ondisk->type;
 305
 306         /*
 307          * Figure out the total number of children's children and
 308          * calculate the average number of elements per child.
 309          *
 310          * The minimum avg_elms is 1 when count > 0.  avg_elms * root_elms
 311          * is always greater or equal to count.
 312          *
 313          * If count == 0 we hit a degenerate case which will cause
 314          * avg_elms to also calculate as 0.
 315          */
 316         if (hammer_debug_general & 0x1000)
 317                 hdkprintf("lockroot %p count %d\n", &lockroot, lockroot.count);
 318         count = 0;
 319         TAILQ_FOREACH(item, &lockroot.list, entry) {
 320                 if (hammer_debug_general & 0x1000)
 321                         hdkprintf("add count %d\n", item->count);
 322                 count += item->count;
 323                 KKASSERT(item->node->ondisk->type == type1);
 324         }
 325         avg_elms = (count + (lockroot.count - 1)) / lockroot.count;
 326         KKASSERT(avg_elms >= 0);
 327
 328         /*
 329          * If the average number of elements per child is too low then
 330          * calculate the desired number of children (n) such that the
 331          * average number of elements is reasonable.
 332          *
 333          * If the desired number of children is 1 then avg_elms will
 334          * wind up being count, which may still be smaller then saturation
 335          * but that is ok.
 336          */
 337         if (count && avg_elms < rebal->saturation) {
 338                 n = (count + (rebal->saturation - 1)) / rebal->saturation;
 339                 avg_elms = (count + (n - 1)) / n;
 340         }
 341
 342         /*
 343          * Pack the elements in the children.  Elements for each item is
 344          * packed into base_item until avg_elms is reached, then base_item
 345          * iterates.
 346          *
 347          * hammer_cursor_moved_element() is called for each element moved
 348          * to update tracked cursors, including the index beyond the last
 349          * element (at count).
 350          *
 351          * Any cursors tracking the internal node itself must also be
 352          * updated, potentially repointing them at a leaf and clearing
 353          * ATEDISK.
 354          */
 355         base_item = TAILQ_FIRST(&lockroot.list);
 356         base_count = 0;
 357         root_count = 0;
 358
 359         TAILQ_FOREACH(item, &lockroot.list, entry) {
 360                 node = item->node;
 361                 KKASSERT(item->count == node->ondisk->count);
 362                 chld_item = TAILQ_FIRST(&item->list);
 363                 for (i = 0; i < item->count; ++i) {
 364                         /*
 365                          * Closeout.  If the next element is at index 0
 366                          * just use the existing separator in the parent.
 367                          */
 368                         if (base_count == avg_elms) {
 369                                 if (i == 0) {
 370                                         elm = &lockroot.node->ondisk->elms[
 371                                                 item->index];
 372                                 } else {
 373                                         elm = &node->ondisk->elms[i];
 374                                 }
 375                                 rebalance_closeout(base_item, base_count, elm);
 376                                 base_item = TAILQ_NEXT(base_item, entry);
 377                                 KKASSERT(base_item);
 378                                 base_count = 0;
 379                                 ++root_count;
 380                         }
 381
 382                         /*
 383                          * Check degenerate no-work case.  Otherwise pack
 384                          * the element.
 385                          *
 386                          * All changes are made to the copy.
 387                          */
 388                         if (item == base_item && i == base_count) {
 389                                 ++base_count;
 390                                 if (chld_item)
 391                                         chld_item = TAILQ_NEXT(chld_item, entry);
 392                                 continue;
 393                         }
 394
 395                         /*
 396                          * Pack element.
 397                          */
 398                         elm = &base_item->copy->elms[base_count];
 399                         *elm = node->ondisk->elms[i];
 400                         base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 401
 402                         /*
 403                          * Adjust the mirror_tid of the target and the
 404                          * internal element linkage.
 405                          *
 406                          * The parent node (lockroot.node) should already
 407                          * have an aggregate mirror_tid so we do not have
 408                          * to update that.  However, it is possible for us
 409                          * to catch a hammer_btree_mirror_propagate() with
 410                          * its pants down.  Update the parent if necessary.
 411                          */
 412                         tid = node->ondisk->mirror_tid;
 413
 414                         if (base_item->copy->mirror_tid < tid) {
 415                                 base_item->copy->mirror_tid = tid;
 416                                 if (lockroot.copy->mirror_tid < tid) {
 417                                         lockroot.copy->mirror_tid = tid;
 418                                         lockroot.flags |=
 419                                                 HAMMER_NODE_LOCK_UPDATED;
 420                                 }
 421                                 if (lockroot.copy->elms[root_count].
 422                                     internal.mirror_tid < tid) {
 423                                         lockroot.copy->elms[root_count].
 424                                                 internal.mirror_tid = tid;
 425                                         lockroot.flags |=
 426                                                 HAMMER_NODE_LOCK_UPDATED;
 427                                 }
 428                                 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 429                         }
 430
 431                         /*
 432                          * We moved elm.  The parent pointers for any
 433                          * children of elm must be repointed.
 434                          */
 435                         if (item != base_item &&
 436                             node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL) {
 437                                 KKASSERT(chld_item);
 438                                 rebalance_parent_ptrs(base_item, base_count,
 439                                                       item, chld_item);
 440                         }
 441                         hammer_cursor_moved_element(item->parent->node,
 442                                                     item->index,
 443                                                     node, i,
 444                                                     base_item->node,
 445                                                     base_count);
 446                         ++base_count;
 447                         if (chld_item)
 448                                 chld_item = TAILQ_NEXT(chld_item, entry);
 449                 }
 450
 451                 /*
 452                  * Always call at the end (i == number of elements) in
 453                  * case a cursor is sitting indexed there.
 454                  */
 455                 hammer_cursor_moved_element(item->parent->node, item->index,
 456                                             node, i,
 457                                             base_item->node, base_count);
 458         }
 459
 460         /*
 461          * Packing complete, close-out base_item using the right-hand
 462          * boundary of the original parent.
 463          *
 464          * If we will be deleting nodes from the root shift the old
 465          * right-hand-boundary to the new ending index.
 466          */
 467         elm = &lockroot.node->ondisk->elms[lockroot.node->ondisk->count];
 468         rebalance_closeout(base_item, base_count, elm);
 469         ++root_count;
 470         if (lockroot.copy->count != root_count) {
 471                 lockroot.copy->count = root_count;
 472                 lockroot.copy->elms[root_count] = *elm;
 473                 lockroot.flags |= HAMMER_NODE_LOCK_UPDATED;
 474         }
 475
 476         /*
 477          * Any extra items beyond base_item are now completely empty and
 478          * can be destroyed.  Queue the destruction up in the copy.  Note
 479          * that none of the destroyed nodes are part of our cursor.
 480          *
 481          * The cursor is locked so it isn't on the tracking list.  It
 482          * should have been pointing at the boundary element (at root_count).
 483          * When deleting elements from the root (which is cursor.node), we
 484          * have to update the cursor.index manually to keep it in bounds.
 485          */
 486         while ((base_item = TAILQ_NEXT(base_item, entry)) != NULL) {
 487                 hammer_cursor_removed_node(base_item->node, lockroot.node,
 488                                            base_count);
 489                 hammer_cursor_deleted_element(lockroot.node, base_count);
 490                 base_item->copy->type = HAMMER_BTREE_TYPE_DELETED;
 491                 base_item->copy->count = 0;
 492                 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 493                 if (cursor->index > lockroot.copy->count)
 494                         --cursor->index;
 495                 ++rebal->stat_deletions;
 496         }
 497
 498         /*
 499          * All done, sync the locked child tree to disk.  This will also
 500          * flush and delete deleted nodes.
 501          */
 502         rebal->stat_nrebal += hammer_btree_sync_copy(cursor, &lockroot);
 503 done:
 504         hammer_btree_unlock_children(cursor->trans->hmp, &lockroot, lcache);
 505         hammer_cursor_downgrade(cursor);
 506         return (error);
 507 }
 508
 509 /*
 510  * Close-out the child base_item.  This node contains base_count
 511  * elements.
 512  *
 513  * If the node is an internal node the right-hand boundary must be
 514  * set to elm.
 515  */
 516 static
 517 void
 518 rebalance_closeout(hammer_node_lock_t base_item, int base_count,
 519                    hammer_btree_elm_t elm)
 520 {
 521         hammer_node_lock_t parent;
 522         hammer_btree_elm_t base_elm;
 523         hammer_btree_elm_t rbound_elm;
 524         uint8_t save;
 525
 526         /*
 527          * Update the count.  NOTE:  base_count can be 0 for the
 528          * degenerate leaf case.
 529          */
 530         if (hammer_debug_general & 0x1000) {
 531                 hdkprintf("%016jx:", (intmax_t)base_item->node->node_offset);
 532         }
 533         if (base_item->copy->count != base_count) {
 534                 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 535                 base_item->copy->count = base_count;
 536                 if (hammer_debug_general & 0x1000)
 537                         kprintf(" (count update)");
 538         }
 539
 540         /*
 541          * If we are closing out an internal node we must assign
 542          * a right-hand boundary.  Use the element contents as the
 543          * right-hand boundary.
 544          *
 545          * Internal nodes are required to have at least one child,
 546          * otherwise the left and right boundary would end up being
 547          * the same element.  Only leaf nodes can be empty.
 548          *
 549          * Rebalancing may cut-off an internal node such that the
 550          * new right hand boundary is the next element anyway, but
 551          * we still have to make sure that subtree_offset, btype,
 552          * and mirror_tid are all 0.
 553          */
 554         if (base_item->copy->type == HAMMER_BTREE_TYPE_INTERNAL) {
 555                 KKASSERT(base_count != 0);
 556                 base_elm = &base_item->copy->elms[base_count];
 557
 558                 if (bcmp(base_elm, elm, sizeof(*elm)) != 0 ||
 559                     elm->internal.subtree_offset ||
 560                     elm->internal.mirror_tid ||
 561                     elm->base.btype) {
 562                         *base_elm = *elm;
 563                         base_elm->internal.subtree_offset = 0;
 564                         base_elm->internal.mirror_tid = 0;
 565                         base_elm->base.btype = 0;
 566                         base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 567                         if (hammer_debug_general & 0x1000)
 568                                 kprintf(" (rhs update)");
 569                 } else {
 570                         if (hammer_debug_general & 0x1000)
 571                                 kprintf(" (rhs same)");
 572                 }
 573         }
 574
 575         /*
 576          * The parent's boundary must be updated.  Be careful to retain
 577          * the btype and non-base internal fields as that information is
 578          * unrelated.
 579          */
 580         parent = base_item->parent;
 581         rbound_elm = &parent->copy->elms[base_item->index + 1];
 582         if (bcmp(&rbound_elm->base, &elm->base, sizeof(elm->base)) != 0) {
 583                 save = rbound_elm->base.btype;
 584                 rbound_elm->base = elm->base;
 585                 rbound_elm->base.btype = save;
 586                 parent->flags |= HAMMER_NODE_LOCK_UPDATED;
 587                 if (hammer_debug_general & 0x1000) {
 588                         kprintf(" (parent bound update %d)",
 589                                 base_item->index + 1);
 590                 }
 591         }
 592         if (hammer_debug_general & 0x1000)
 593                 kprintf("\n");
 594 }
 595
 596 /*
 597  * An element in item has moved to base_item.  We must update the parent
 598  * pointer of the node the element points to (which is chld_item).
 599  */
 600 static
 601 void
 602 rebalance_parent_ptrs(hammer_node_lock_t base_item, int index,
 603                       hammer_node_lock_t item, hammer_node_lock_t chld_item)
 604 {
 605         KKASSERT(chld_item->node->ondisk->parent == item->node->node_offset);
 606         chld_item->copy->parent = base_item->node->node_offset;
 607         chld_item->flags |= HAMMER_NODE_LOCK_UPDATED;
 608         hammer_cursor_parent_changed(chld_item->node,
 609                                      item->node, base_item->node, index);
 610 }