2 * Copyright (c) 2009 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
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8 * modification, are permitted provided that the following conditions
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21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 static int rebalance_node(struct hammer_ioc_rebalance *rebal,
38 hammer_cursor_t cursor);
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);
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.
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.
54 hammer_ioc_rebalance(hammer_transaction_t trans, hammer_inode_t ip,
55 struct hammer_ioc_rebalance *rebal)
57 struct hammer_cursor cursor;
58 hammer_btree_leaf_elm_t elm;
62 if ((rebal->key_beg.localization | rebal->key_end.localization) &
63 HAMMER_LOCALIZE_PSEUDOFS_MASK) {
66 if (rebal->key_beg.localization > rebal->key_end.localization)
68 if (rebal->key_beg.localization == rebal->key_end.localization) {
69 if (rebal->key_beg.obj_id > rebal->key_end.obj_id)
71 /* key-space limitations - no check needed */
73 if (rebal->saturation < HAMMER_BTREE_INT_ELMS / 2)
74 rebal->saturation = HAMMER_BTREE_INT_ELMS / 2;
75 if (rebal->saturation > HAMMER_BTREE_INT_ELMS)
76 rebal->saturation = HAMMER_BTREE_INT_ELMS;
78 rebal->key_cur = rebal->key_beg;
79 rebal->key_cur.localization &= HAMMER_LOCALIZE_MASK;
80 rebal->key_cur.localization += ip->obj_localization;
82 seq = trans->hmp->flusher.act;
85 * Scan forwards. Retries typically occur if a deadlock is detected.
88 error = hammer_init_cursor(trans, &cursor, NULL, NULL);
90 hammer_done_cursor(&cursor);
93 cursor.key_beg = rebal->key_cur;
94 cursor.key_end = rebal->key_end;
95 cursor.key_end.localization &= HAMMER_LOCALIZE_MASK;
96 cursor.key_end.localization += ip->obj_localization;
97 cursor.flags |= HAMMER_CURSOR_END_INCLUSIVE;
98 cursor.flags |= HAMMER_CURSOR_BACKEND;
101 * Cause internal nodes to be returned on the way up. Internal nodes
102 * are not returned on the way down so we can create a degenerate
103 * case to handle internal nodes as a trailing function of their
106 * Note that by not setting INSERTING or PRUNING no boundary
107 * corrections will be made and a sync lock is not needed for the
108 * B-Tree scan itself.
110 cursor.flags |= HAMMER_CURSOR_REBLOCKING;
112 error = hammer_btree_first(&cursor);
116 * We only care about internal nodes visited for the last
117 * time on the way up... that is, a trailing scan of the
118 * internal node after all of its children have been recursed
121 if (cursor.node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL) {
123 * Leave cursor.index alone, we want to recurse
124 * through all children of the internal node before
127 * Process the internal node on the way up after
128 * the last child's sub-tree has been balanced.
130 if (cursor.index == cursor.node->ondisk->count - 1) {
131 hammer_sync_lock_sh(trans);
132 error = rebalance_node(rebal, &cursor);
133 hammer_sync_unlock(trans);
137 * We don't need to iterate through all the leaf
138 * elements, we only care about the parent (internal)
141 cursor.index = cursor.node->ondisk->count - 1;
147 * Update returned scan position and do a flush if
150 * WARNING: We extract the base using the leaf element
151 * type but this could be an internal node. The
152 * base is the same either way.
154 * However, due to the rebalancing operation the
155 * cursor position may have exceeded the right-hand
158 * WARNING: See warnings in hammer_unlock_cursor()
161 elm = &cursor.node->ondisk->elms[cursor.index].leaf;
162 rebal->key_cur = elm->base;
163 ++rebal->stat_ncount;
165 while (hammer_flusher_meta_halflimit(trans->hmp) ||
166 hammer_flusher_undo_exhausted(trans, 2)) {
167 hammer_unlock_cursor(&cursor);
168 hammer_flusher_wait(trans->hmp, seq);
169 hammer_lock_cursor(&cursor);
170 seq = hammer_flusher_async_one(trans->hmp);
174 * Before iterating check if the rebalance operation caused
175 * the cursor to index past the right-hand boundary and make
176 * sure to stop if it does. Otherwise the iteration may
177 * panic e.g. due to the key maxing out its fields and no
178 * longer being within the strict bounds of the root node.
180 if (hammer_btree_cmp(&rebal->key_cur, &cursor.key_end) > 0) {
181 rebal->key_cur = cursor.key_end;
186 * Iterate, stop if a signal was received.
188 if ((error = hammer_signal_check(trans->hmp)) != 0)
190 error = hammer_btree_iterate(&cursor);
194 hammer_done_cursor(&cursor);
195 if (error == EDEADLK) {
196 ++rebal->stat_collisions;
199 if (error == EINTR) {
200 rebal->head.flags |= HAMMER_IOC_HEAD_INTR;
204 rebal->key_cur.localization &= HAMMER_LOCALIZE_MASK;
209 * Rebalance an internal node, called via a trailing upward recursion.
210 * All the children have already been individually rebalanced.
212 * To rebalance we scan the elements in the children and pack them,
213 * so we actually need to lock the children and the children's children.
217 * C C C C C C C children (first level) (internal or leaf nodes)
218 * children's elements (second level)
220 * <<<---------- pack children's elements, possibly remove excess
221 * children after packing.
223 * NOTE: The mirror_tids, parent pointers, and child pointers must be updated.
224 * Any live tracked B-Tree nodes must be updated (we worm out of that
225 * by not allowing any). And boundary elements must be preserved.
227 * NOTE: If the children are leaf nodes we may have a degenerate case
228 * case where there are no elements in the leafs.
233 rebalance_node(struct hammer_ioc_rebalance *rebal, hammer_cursor_t cursor)
235 struct hammer_node_lock lockroot;
236 hammer_node_lock_t base_item;
237 hammer_node_lock_t chld_item;
238 hammer_node_lock_t item;
239 hammer_btree_elm_t elm;
251 * Lock the parent node via the cursor, collect and lock our
252 * children and children's children.
254 * By the way, this is a LOT of locks.
256 hammer_node_lock_init(&lockroot, cursor->node);
257 error = hammer_cursor_upgrade(cursor);
260 error = hammer_btree_lock_children(cursor, 2, &lockroot);
265 * Make a copy of all the locked on-disk data to simplify the element
266 * shifting we are going to have to do. We will modify the copy
269 hammer_btree_lock_copy(cursor, &lockroot);
272 * Look at the first child node.
274 if (TAILQ_FIRST(&lockroot.list) == NULL)
276 type1 = TAILQ_FIRST(&lockroot.list)->node->ondisk->type;
279 * Figure out the total number of children's children and
280 * calculate the average number of elements per child.
282 * The minimum avg_elms is 1 when count > 0. avg_elms * root_elms
283 * is always greater or equal to count.
285 * If count == 0 we hit a degenerate case which will cause
286 * avg_elms to also calculate as 0.
288 if (hammer_debug_general & 0x1000)
289 kprintf("lockroot %p count %d\n", &lockroot, lockroot.count);
291 TAILQ_FOREACH(item, &lockroot.list, entry) {
292 if (hammer_debug_general & 0x1000)
293 kprintf("add count %d\n", item->count);
294 count += item->count;
295 KKASSERT(item->node->ondisk->type == type1);
297 avg_elms = (count + (lockroot.count - 1)) / lockroot.count;
298 KKASSERT(avg_elms >= 0);
301 * If the average number of elements per child is too low then
302 * calculate the desired number of children (n) such that the
303 * average number of elements is reasonable.
305 * If the desired number of children is 1 then avg_elms will
306 * wind up being count, which may still be smaller then saturation
309 if (count && avg_elms < rebal->saturation) {
310 n = (count + (rebal->saturation - 1)) / rebal->saturation;
311 avg_elms = (count + (n - 1)) / n;
315 * Pack the elements in the children. Elements for each item is
316 * packed into base_item until avg_elms is reached, then base_item
319 * hammer_cursor_moved_element() is called for each element moved
320 * to update tracked cursors, including the index beyond the last
321 * element (at count).
323 base_item = TAILQ_FIRST(&lockroot.list);
327 TAILQ_FOREACH(item, &lockroot.list, entry) {
329 KKASSERT(item->count == node->ondisk->count);
330 chld_item = TAILQ_FIRST(&item->list);
331 for (i = 0; i < item->count; ++i) {
333 * Closeout. If the next element is at index 0
334 * just use the existing separator in the parent.
336 if (base_count == avg_elms) {
338 elm = &lockroot.node->ondisk->elms[
341 elm = &node->ondisk->elms[i];
343 rebalance_closeout(base_item, base_count, elm);
344 base_item = TAILQ_NEXT(base_item, entry);
351 * Check degenerate no-work case. Otherwise pack
354 * All changes are made to the copy.
356 if (item == base_item && i == base_count) {
359 chld_item = TAILQ_NEXT(chld_item, entry);
366 elm = &base_item->copy->elms[base_count];
367 *elm = node->ondisk->elms[i];
368 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
371 * Adjust the mirror_tid of the target. The parent
372 * node (lockroot.node) should already have an
373 * aggregate mirror_tid so we do not have to update
376 * However, it is possible for us to catch a
377 * hammer_btree_mirror_propagate() with its pants
378 * down. Update the parent if necessary.
380 if (base_item->copy->mirror_tid <
381 node->ondisk->mirror_tid) {
382 base_item->copy->mirror_tid =
383 node->ondisk->mirror_tid;
384 if (lockroot.copy->mirror_tid <
385 node->ondisk->mirror_tid) {
386 lockroot.copy->mirror_tid =
387 node->ondisk->mirror_tid;
389 HAMMER_NODE_LOCK_UPDATED;
391 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
395 * We moved elm. The parent pointers for any
396 * children of elm must be repointed.
398 if (item != base_item &&
399 node->ondisk->type == HAMMER_BTREE_TYPE_INTERNAL) {
401 rebalance_parent_ptrs(base_item, base_count,
404 hammer_cursor_moved_element(node, base_item->node,
408 chld_item = TAILQ_NEXT(chld_item, entry);
412 * Always call at the end (i == number of elements) in
413 * case a cursor is sitting indexed there.
415 hammer_cursor_moved_element(node, base_item->node,
420 * Packing complete, close-out base_item using the right-hand
421 * boundary of the original parent.
423 * If we will be deleting nodes from the root shift the old
424 * right-hand-boundary to the new ending index.
426 elm = &lockroot.node->ondisk->elms[lockroot.node->ondisk->count];
427 rebalance_closeout(base_item, base_count, elm);
429 if (lockroot.copy->count != root_count) {
430 lockroot.copy->count = root_count;
431 lockroot.copy->elms[root_count] = *elm;
432 lockroot.flags |= HAMMER_NODE_LOCK_UPDATED;
436 * Any extra items beyond base_item are now completely empty and
437 * can be destroyed. Queue the destruction up in the copy. Note
438 * that none of the destroyed nodes are part of our cursor.
440 * The cursor is locked so it isn't on the tracking list. It
441 * should have been pointing at the boundary element (at root_count).
442 * When deleting elements from the root (which is cursor.node), we
443 * have to update the cursor.index manually to keep it in bounds.
445 while ((base_item = TAILQ_NEXT(base_item, entry)) != NULL) {
446 hammer_cursor_removed_node(base_item->node, lockroot.node,
448 hammer_cursor_deleted_element(lockroot.node, base_count);
449 base_item->copy->type = HAMMER_BTREE_TYPE_DELETED;
450 base_item->copy->count = 0;
451 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
452 if (cursor->index > lockroot.copy->count)
454 ++rebal->stat_deletions;
458 * All done, sync the locked child tree to disk. This will also
459 * flush and delete deleted nodes.
461 rebal->stat_nrebal += hammer_btree_sync_copy(cursor, &lockroot);
463 hammer_btree_unlock_children(cursor, &lockroot);
464 hammer_cursor_downgrade(cursor);
469 * Close-out the child base_item. This node contains base_count
472 * If the node is an internal node the right-hand boundary must be
477 rebalance_closeout(hammer_node_lock_t base_item, int base_count,
478 hammer_btree_elm_t elm)
480 hammer_node_lock_t parent;
481 hammer_btree_elm_t base_elm;
482 hammer_btree_elm_t rbound_elm;
486 * Update the count. NOTE: base_count can be 0 for the
487 * degenerate leaf case.
489 if (hammer_debug_general & 0x1000) {
490 kprintf("rebalance_closeout %016llx:",
491 (long long)base_item->node->node_offset);
493 if (base_item->copy->count != base_count) {
494 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
495 base_item->copy->count = base_count;
496 if (hammer_debug_general & 0x1000)
497 kprintf(" (count update)");
501 * If we are closing out an internal node we must assign
502 * a right-hand boundary. Use the element contents as the
503 * right-hand boundary.
505 * Internal nodes are required to have at least one child,
506 * otherwise the left and right boundary would end up being
507 * the same element. Only leaf nodes can be empty.
509 * Rebalancing may cut-off an internal node such that the
510 * new right hand boundary is the next element anyway, but
511 * we still have to make sure that subtree_offset, btype,
512 * and mirror_tid are all 0.
514 if (base_item->copy->type == HAMMER_BTREE_TYPE_INTERNAL) {
515 KKASSERT(base_count != 0);
516 base_elm = &base_item->copy->elms[base_count];
518 if (bcmp(base_elm, elm, sizeof(*elm)) != 0 ||
519 elm->internal.subtree_offset ||
520 elm->internal.mirror_tid ||
523 base_elm->internal.subtree_offset = 0;
524 base_elm->internal.mirror_tid = 0;
525 base_elm->base.btype = 0;
526 base_item->flags |= HAMMER_NODE_LOCK_UPDATED;
527 if (hammer_debug_general & 0x1000)
528 kprintf(" (rhs update)");
530 if (hammer_debug_general & 0x1000)
531 kprintf(" (rhs same)");
536 * The parent's boundary must be updated. Be careful to retain
537 * the btype and non-base internal fields as that information is
540 parent = base_item->parent;
541 rbound_elm = &parent->copy->elms[base_item->index + 1];
542 if (bcmp(&rbound_elm->base, &elm->base, sizeof(elm->base)) != 0) {
543 save = rbound_elm->base.btype;
544 rbound_elm->base = elm->base;
545 rbound_elm->base.btype = save;
546 parent->flags |= HAMMER_NODE_LOCK_UPDATED;
547 if (hammer_debug_general & 0x1000) {
548 kprintf(" (parent bound update %d)",
549 base_item->index + 1);
552 if (hammer_debug_general & 0x1000)
557 * An element in item has moved to base_item. We must update the parent
558 * pointer of the node the element points to (which is chld_item).
562 rebalance_parent_ptrs(hammer_node_lock_t base_item, int index,
563 hammer_node_lock_t item, hammer_node_lock_t chld_item)
565 KKASSERT(chld_item->node->ondisk->parent == item->node->node_offset);
566 chld_item->copy->parent = base_item->node->node_offset;
567 chld_item->flags |= HAMMER_NODE_LOCK_UPDATED;
568 hammer_cursor_parent_changed(chld_item->node,
569 item->node, base_item->node, index);