1 // SPDX-License-Identifier: GPL-2.0
4 #include "btree_cache.h"
6 #include "btree_iter.h"
7 #include "btree_locking.h"
10 #include <linux/prefetch.h>
11 #include <linux/sched/mm.h>
12 #include <trace/events/bcachefs.h>
14 const char * const bch2_btree_ids[] = {
15 #define x(kwd, val, name) name,
21 void bch2_recalc_btree_reserve(struct bch_fs *c)
23 unsigned i, reserve = 16;
25 if (!c->btree_roots[0].b)
28 for (i = 0; i < BTREE_ID_NR; i++)
29 if (c->btree_roots[i].b)
30 reserve += min_t(unsigned, 1,
31 c->btree_roots[i].b->level) * 8;
33 c->btree_cache.reserve = reserve;
36 static inline unsigned btree_cache_can_free(struct btree_cache *bc)
38 return max_t(int, 0, bc->used - bc->reserve);
41 static void __btree_node_data_free(struct bch_fs *c, struct btree *b)
43 EBUG_ON(btree_node_write_in_flight(b));
45 kvpfree(b->data, btree_bytes(c));
47 bch2_btree_keys_free(b);
50 static void btree_node_data_free(struct bch_fs *c, struct btree *b)
52 struct btree_cache *bc = &c->btree_cache;
54 __btree_node_data_free(c, b);
56 list_move(&b->list, &bc->freed);
59 static int bch2_btree_cache_cmp_fn(struct rhashtable_compare_arg *arg,
62 const struct btree *b = obj;
63 const u64 *v = arg->key;
65 return PTR_HASH(&b->key) == *v ? 0 : 1;
68 static const struct rhashtable_params bch_btree_cache_params = {
69 .head_offset = offsetof(struct btree, hash),
70 .key_offset = offsetof(struct btree, key.v),
71 .key_len = sizeof(struct bch_extent_ptr),
72 .obj_cmpfn = bch2_btree_cache_cmp_fn,
75 static void btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)
77 struct btree_cache *bc = &c->btree_cache;
79 b->data = kvpmalloc(btree_bytes(c), gfp);
83 if (bch2_btree_keys_alloc(b, btree_page_order(c), gfp))
87 list_move(&b->list, &bc->freeable);
90 kvpfree(b->data, btree_bytes(c));
92 list_move(&b->list, &bc->freed);
95 static struct btree *btree_node_mem_alloc(struct bch_fs *c, gfp_t gfp)
97 struct btree *b = kzalloc(sizeof(struct btree), gfp);
101 bkey_btree_ptr_init(&b->key);
102 six_lock_init(&b->lock);
103 INIT_LIST_HEAD(&b->list);
104 INIT_LIST_HEAD(&b->write_blocked);
106 btree_node_data_alloc(c, b, gfp);
107 return b->data ? b : NULL;
110 /* Btree in memory cache - hash table */
112 void bch2_btree_node_hash_remove(struct btree_cache *bc, struct btree *b)
114 rhashtable_remove_fast(&bc->table, &b->hash, bch_btree_cache_params);
116 /* Cause future lookups for this node to fail: */
117 PTR_HASH(&b->key) = 0;
120 int __bch2_btree_node_hash_insert(struct btree_cache *bc, struct btree *b)
122 return rhashtable_lookup_insert_fast(&bc->table, &b->hash,
123 bch_btree_cache_params);
126 int bch2_btree_node_hash_insert(struct btree_cache *bc, struct btree *b,
127 unsigned level, enum btree_id id)
134 mutex_lock(&bc->lock);
135 ret = __bch2_btree_node_hash_insert(bc, b);
137 list_add(&b->list, &bc->live);
138 mutex_unlock(&bc->lock);
144 static inline struct btree *btree_cache_find(struct btree_cache *bc,
145 const struct bkey_i *k)
147 return rhashtable_lookup_fast(&bc->table, &PTR_HASH(k),
148 bch_btree_cache_params);
152 * this version is for btree nodes that have already been freed (we're not
153 * reaping a real btree node)
155 static int __btree_node_reclaim(struct bch_fs *c, struct btree *b, bool flush)
157 struct btree_cache *bc = &c->btree_cache;
160 lockdep_assert_held(&bc->lock);
162 if (!six_trylock_intent(&b->lock))
165 if (!six_trylock_write(&b->lock))
166 goto out_unlock_intent;
168 if (btree_node_noevict(b))
171 if (!btree_node_may_write(b))
174 if (btree_node_dirty(b) &&
175 test_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags))
178 if (btree_node_dirty(b) ||
179 btree_node_write_in_flight(b) ||
180 btree_node_read_in_flight(b)) {
184 wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
185 TASK_UNINTERRUPTIBLE);
188 * Using the underscore version because we don't want to compact
189 * bsets after the write, since this node is about to be evicted
190 * - unless btree verify mode is enabled, since it runs out of
191 * the post write cleanup:
193 if (verify_btree_ondisk(c))
194 bch2_btree_node_write(c, b, SIX_LOCK_intent);
196 __bch2_btree_node_write(c, b, SIX_LOCK_read);
198 /* wait for any in flight btree write */
199 btree_node_wait_on_io(b);
202 if (PTR_HASH(&b->key) && !ret)
203 trace_btree_node_reap(c, b);
206 six_unlock_write(&b->lock);
208 six_unlock_intent(&b->lock);
213 static int btree_node_reclaim(struct bch_fs *c, struct btree *b)
215 return __btree_node_reclaim(c, b, false);
218 static int btree_node_write_and_reclaim(struct bch_fs *c, struct btree *b)
220 return __btree_node_reclaim(c, b, true);
223 static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
224 struct shrink_control *sc)
226 struct bch_fs *c = container_of(shrink, struct bch_fs,
228 struct btree_cache *bc = &c->btree_cache;
230 unsigned long nr = sc->nr_to_scan;
231 unsigned long can_free;
232 unsigned long touched = 0;
233 unsigned long freed = 0;
236 if (btree_shrinker_disabled(c))
239 /* Return -1 if we can't do anything right now */
240 if (sc->gfp_mask & __GFP_IO)
241 mutex_lock(&bc->lock);
242 else if (!mutex_trylock(&bc->lock))
246 * It's _really_ critical that we don't free too many btree nodes - we
247 * have to always leave ourselves a reserve. The reserve is how we
248 * guarantee that allocating memory for a new btree node can always
249 * succeed, so that inserting keys into the btree can always succeed and
250 * IO can always make forward progress:
252 nr /= btree_pages(c);
253 can_free = btree_cache_can_free(bc);
254 nr = min_t(unsigned long, nr, can_free);
257 list_for_each_entry_safe(b, t, &bc->freeable, list) {
264 !btree_node_reclaim(c, b)) {
265 btree_node_data_free(c, b);
266 six_unlock_write(&b->lock);
267 six_unlock_intent(&b->lock);
272 list_for_each_entry_safe(b, t, &bc->live, list) {
277 if (&t->list != &bc->live)
278 list_move_tail(&bc->live, &t->list);
282 if (!btree_node_accessed(b) &&
283 !btree_node_reclaim(c, b)) {
284 /* can't call bch2_btree_node_hash_remove under lock */
286 if (&t->list != &bc->live)
287 list_move_tail(&bc->live, &t->list);
289 btree_node_data_free(c, b);
290 mutex_unlock(&bc->lock);
292 bch2_btree_node_hash_remove(bc, b);
293 six_unlock_write(&b->lock);
294 six_unlock_intent(&b->lock);
299 if (sc->gfp_mask & __GFP_IO)
300 mutex_lock(&bc->lock);
301 else if (!mutex_trylock(&bc->lock))
305 clear_btree_node_accessed(b);
308 mutex_unlock(&bc->lock);
310 return (unsigned long) freed * btree_pages(c);
313 static unsigned long bch2_btree_cache_count(struct shrinker *shrink,
314 struct shrink_control *sc)
316 struct bch_fs *c = container_of(shrink, struct bch_fs,
318 struct btree_cache *bc = &c->btree_cache;
320 if (btree_shrinker_disabled(c))
323 return btree_cache_can_free(bc) * btree_pages(c);
326 void bch2_fs_btree_cache_exit(struct bch_fs *c)
328 struct btree_cache *bc = &c->btree_cache;
332 if (bc->shrink.list.next)
333 unregister_shrinker(&bc->shrink);
335 mutex_lock(&bc->lock);
337 #ifdef CONFIG_BCACHEFS_DEBUG
339 list_move(&c->verify_data->list, &bc->live);
341 kvpfree(c->verify_ondisk, btree_bytes(c));
344 for (i = 0; i < BTREE_ID_NR; i++)
345 if (c->btree_roots[i].b)
346 list_add(&c->btree_roots[i].b->list, &bc->live);
348 list_splice(&bc->freeable, &bc->live);
350 while (!list_empty(&bc->live)) {
351 b = list_first_entry(&bc->live, struct btree, list);
353 BUG_ON(btree_node_read_in_flight(b) ||
354 btree_node_write_in_flight(b));
356 if (btree_node_dirty(b))
357 bch2_btree_complete_write(c, b, btree_current_write(b));
358 clear_btree_node_dirty(b);
360 btree_node_data_free(c, b);
363 while (!list_empty(&bc->freed)) {
364 b = list_first_entry(&bc->freed, struct btree, list);
369 mutex_unlock(&bc->lock);
371 if (bc->table_init_done)
372 rhashtable_destroy(&bc->table);
375 int bch2_fs_btree_cache_init(struct bch_fs *c)
377 struct btree_cache *bc = &c->btree_cache;
381 pr_verbose_init(c->opts, "");
383 ret = rhashtable_init(&bc->table, &bch_btree_cache_params);
387 bc->table_init_done = true;
389 bch2_recalc_btree_reserve(c);
391 for (i = 0; i < bc->reserve; i++)
392 if (!btree_node_mem_alloc(c, GFP_KERNEL)) {
397 list_splice_init(&bc->live, &bc->freeable);
399 #ifdef CONFIG_BCACHEFS_DEBUG
400 mutex_init(&c->verify_lock);
402 c->verify_ondisk = kvpmalloc(btree_bytes(c), GFP_KERNEL);
403 if (!c->verify_ondisk) {
408 c->verify_data = btree_node_mem_alloc(c, GFP_KERNEL);
409 if (!c->verify_data) {
414 list_del_init(&c->verify_data->list);
417 bc->shrink.count_objects = bch2_btree_cache_count;
418 bc->shrink.scan_objects = bch2_btree_cache_scan;
419 bc->shrink.seeks = 4;
420 bc->shrink.batch = btree_pages(c) * 2;
421 register_shrinker(&bc->shrink);
423 pr_verbose_init(c->opts, "ret %i", ret);
427 void bch2_fs_btree_cache_init_early(struct btree_cache *bc)
429 mutex_init(&bc->lock);
430 INIT_LIST_HEAD(&bc->live);
431 INIT_LIST_HEAD(&bc->freeable);
432 INIT_LIST_HEAD(&bc->freed);
436 * We can only have one thread cannibalizing other cached btree nodes at a time,
437 * or we'll deadlock. We use an open coded mutex to ensure that, which a
438 * cannibalize_bucket() will take. This means every time we unlock the root of
439 * the btree, we need to release this lock if we have it held.
441 void bch2_btree_cache_cannibalize_unlock(struct bch_fs *c)
443 struct btree_cache *bc = &c->btree_cache;
445 if (bc->alloc_lock == current) {
446 trace_btree_node_cannibalize_unlock(c);
447 bc->alloc_lock = NULL;
448 closure_wake_up(&bc->alloc_wait);
452 int bch2_btree_cache_cannibalize_lock(struct bch_fs *c, struct closure *cl)
454 struct btree_cache *bc = &c->btree_cache;
455 struct task_struct *old;
457 old = cmpxchg(&bc->alloc_lock, NULL, current);
458 if (old == NULL || old == current)
462 trace_btree_node_cannibalize_lock_fail(c);
466 closure_wait(&bc->alloc_wait, cl);
468 /* Try again, after adding ourselves to waitlist */
469 old = cmpxchg(&bc->alloc_lock, NULL, current);
470 if (old == NULL || old == current) {
472 closure_wake_up(&bc->alloc_wait);
476 trace_btree_node_cannibalize_lock_fail(c);
480 trace_btree_node_cannibalize_lock(c);
484 static struct btree *btree_node_cannibalize(struct bch_fs *c)
486 struct btree_cache *bc = &c->btree_cache;
489 list_for_each_entry_reverse(b, &bc->live, list)
490 if (!btree_node_reclaim(c, b))
494 list_for_each_entry_reverse(b, &bc->live, list)
495 if (!btree_node_write_and_reclaim(c, b))
499 * Rare case: all nodes were intent-locked.
502 WARN_ONCE(1, "btree cache cannibalize failed\n");
507 struct btree *bch2_btree_node_mem_alloc(struct bch_fs *c)
509 struct btree_cache *bc = &c->btree_cache;
511 u64 start_time = local_clock();
514 flags = memalloc_nofs_save();
515 mutex_lock(&bc->lock);
518 * btree_free() doesn't free memory; it sticks the node on the end of
519 * the list. Check if there's any freed nodes there:
521 list_for_each_entry(b, &bc->freeable, list)
522 if (!btree_node_reclaim(c, b))
526 * We never free struct btree itself, just the memory that holds the on
527 * disk node. Check the freed list before allocating a new one:
529 list_for_each_entry(b, &bc->freed, list)
530 if (!btree_node_reclaim(c, b)) {
531 btree_node_data_alloc(c, b, __GFP_NOWARN|GFP_NOIO);
535 six_unlock_write(&b->lock);
536 six_unlock_intent(&b->lock);
540 b = btree_node_mem_alloc(c, __GFP_NOWARN|GFP_NOIO);
544 BUG_ON(!six_trylock_intent(&b->lock));
545 BUG_ON(!six_trylock_write(&b->lock));
547 BUG_ON(btree_node_hashed(b));
548 BUG_ON(btree_node_write_in_flight(b));
550 list_del_init(&b->list);
551 mutex_unlock(&bc->lock);
552 memalloc_nofs_restore(flags);
559 b->whiteout_u64s = 0;
560 b->uncompacted_whiteout_u64s = 0;
561 bch2_btree_keys_init(b, &c->expensive_debug_checks);
563 bch2_time_stats_update(&c->times[BCH_TIME_btree_node_mem_alloc],
568 /* Try to cannibalize another cached btree node: */
569 if (bc->alloc_lock == current) {
570 b = btree_node_cannibalize(c);
571 list_del_init(&b->list);
572 mutex_unlock(&bc->lock);
574 bch2_btree_node_hash_remove(bc, b);
576 trace_btree_node_cannibalize(c);
580 mutex_unlock(&bc->lock);
581 return ERR_PTR(-ENOMEM);
584 /* Slowpath, don't want it inlined into btree_iter_traverse() */
585 static noinline struct btree *bch2_btree_node_fill(struct bch_fs *c,
586 struct btree_iter *iter,
587 const struct bkey_i *k,
589 enum six_lock_type lock_type,
592 struct btree_cache *bc = &c->btree_cache;
596 * Parent node must be locked, else we could read in a btree node that's
599 BUG_ON(!btree_node_locked(iter, level + 1));
600 BUG_ON(level >= BTREE_MAX_DEPTH);
602 b = bch2_btree_node_mem_alloc(c);
606 bkey_copy(&b->key, k);
607 if (bch2_btree_node_hash_insert(bc, b, level, iter->btree_id)) {
608 /* raced with another fill: */
610 /* mark as unhashed... */
611 PTR_HASH(&b->key) = 0;
613 mutex_lock(&bc->lock);
614 list_add(&b->list, &bc->freeable);
615 mutex_unlock(&bc->lock);
617 six_unlock_write(&b->lock);
618 six_unlock_intent(&b->lock);
623 * If the btree node wasn't cached, we can't drop our lock on
624 * the parent until after it's added to the cache - because
625 * otherwise we could race with a btree_split() freeing the node
626 * we're trying to lock.
628 * But the deadlock described below doesn't exist in this case,
629 * so it's safe to not drop the parent lock until here:
631 if (btree_node_read_locked(iter, level + 1))
632 btree_node_unlock(iter, level + 1);
634 bch2_btree_node_read(c, b, sync);
636 six_unlock_write(&b->lock);
639 six_unlock_intent(&b->lock);
643 if (lock_type == SIX_LOCK_read)
644 six_lock_downgrade(&b->lock);
650 * bch_btree_node_get - find a btree node in the cache and lock it, reading it
651 * in from disk if necessary.
653 * If IO is necessary and running under generic_make_request, returns -EAGAIN.
655 * The btree node will have either a read or a write lock held, depending on
656 * the @write parameter.
658 struct btree *bch2_btree_node_get(struct bch_fs *c, struct btree_iter *iter,
659 const struct bkey_i *k, unsigned level,
660 enum six_lock_type lock_type)
662 struct btree_cache *bc = &c->btree_cache;
667 * XXX: locking optimization
669 * we can make the locking looser here - caller can drop lock on parent
670 * node before locking child node (and potentially blocking): we just
671 * have to have bch2_btree_node_fill() call relock on the parent and
672 * return -EINTR if that fails
674 EBUG_ON(!btree_node_locked(iter, level + 1));
675 EBUG_ON(level >= BTREE_MAX_DEPTH);
677 b = btree_cache_find(bc, k);
680 * We must have the parent locked to call bch2_btree_node_fill(),
681 * else we could read in a btree node from disk that's been
684 b = bch2_btree_node_fill(c, iter, k, level, lock_type, true);
686 /* We raced and found the btree node in the cache */
694 * There's a potential deadlock with splits and insertions into
695 * interior nodes we have to avoid:
697 * The other thread might be holding an intent lock on the node
698 * we want, and they want to update its parent node so they're
699 * going to upgrade their intent lock on the parent node to a
702 * But if we're holding a read lock on the parent, and we're
703 * trying to get the intent lock they're holding, we deadlock.
705 * So to avoid this we drop the read locks on parent nodes when
706 * we're starting to take intent locks - and handle the race.
708 * The race is that they might be about to free the node we
709 * want, and dropping our read lock on the parent node lets them
710 * update the parent marking the node we want as freed, and then
713 * To guard against this, btree nodes are evicted from the cache
714 * when they're freed - and PTR_HASH() is zeroed out, which we
715 * check for after we lock the node.
717 * Then, bch2_btree_node_relock() on the parent will fail - because
718 * the parent was modified, when the pointer to the node we want
719 * was removed - and we'll bail out:
721 if (btree_node_read_locked(iter, level + 1))
722 btree_node_unlock(iter, level + 1);
724 if (!btree_node_lock(b, k->k.p, level, iter, lock_type))
725 return ERR_PTR(-EINTR);
727 if (unlikely(PTR_HASH(&b->key) != PTR_HASH(k) ||
730 six_unlock_type(&b->lock, lock_type);
731 if (bch2_btree_node_relock(iter, level + 1))
734 trace_trans_restart_btree_node_reused(iter->trans->ip);
735 return ERR_PTR(-EINTR);
739 wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
740 TASK_UNINTERRUPTIBLE);
742 prefetch(b->aux_data);
744 for_each_bset(b, t) {
745 void *p = (u64 *) b->aux_data + t->aux_data_offset;
747 prefetch(p + L1_CACHE_BYTES * 0);
748 prefetch(p + L1_CACHE_BYTES * 1);
749 prefetch(p + L1_CACHE_BYTES * 2);
752 /* avoid atomic set bit if it's not needed: */
753 if (btree_node_accessed(b))
754 set_btree_node_accessed(b);
756 if (unlikely(btree_node_read_error(b))) {
757 six_unlock_type(&b->lock, lock_type);
758 return ERR_PTR(-EIO);
761 EBUG_ON(b->btree_id != iter->btree_id ||
762 BTREE_NODE_LEVEL(b->data) != level ||
763 bkey_cmp(b->data->max_key, k->k.p));
768 struct btree *bch2_btree_node_get_sibling(struct bch_fs *c,
769 struct btree_iter *iter,
771 enum btree_node_sibling sib)
773 struct btree_trans *trans = iter->trans;
774 struct btree *parent;
775 struct btree_node_iter node_iter;
776 struct bkey_packed *k;
778 struct btree *ret = NULL;
779 unsigned level = b->level;
781 parent = btree_iter_node(iter, level + 1);
785 if (!bch2_btree_node_relock(iter, level + 1)) {
786 ret = ERR_PTR(-EINTR);
790 node_iter = iter->l[parent->level].iter;
792 k = bch2_btree_node_iter_peek_all(&node_iter, parent);
793 BUG_ON(bkey_cmp_left_packed(parent, k, &b->key.k.p));
795 k = sib == btree_prev_sib
796 ? bch2_btree_node_iter_prev(&node_iter, parent)
797 : (bch2_btree_node_iter_advance(&node_iter, parent),
798 bch2_btree_node_iter_peek(&node_iter, parent));
802 bch2_bkey_unpack(parent, &tmp.k, k);
804 ret = bch2_btree_node_get(c, iter, &tmp.k, level,
807 if (PTR_ERR_OR_ZERO(ret) == -EINTR && !trans->nounlock) {
808 struct btree_iter *linked;
810 if (!bch2_btree_node_relock(iter, level + 1))
814 * We might have got -EINTR because trylock failed, and we're
815 * holding other locks that would cause us to deadlock:
817 trans_for_each_iter(trans, linked)
818 if (btree_iter_cmp(iter, linked) < 0)
819 __bch2_btree_iter_unlock(linked);
821 if (sib == btree_prev_sib)
822 btree_node_unlock(iter, level);
824 ret = bch2_btree_node_get(c, iter, &tmp.k, level,
828 * before btree_iter_relock() calls btree_iter_verify_locks():
830 if (btree_lock_want(iter, level + 1) == BTREE_NODE_UNLOCKED)
831 btree_node_unlock(iter, level + 1);
833 if (!bch2_btree_node_relock(iter, level)) {
834 btree_iter_set_dirty(iter, BTREE_ITER_NEED_RELOCK);
837 six_unlock_intent(&ret->lock);
838 ret = ERR_PTR(-EINTR);
842 bch2_trans_relock(trans);
845 if (btree_lock_want(iter, level + 1) == BTREE_NODE_UNLOCKED)
846 btree_node_unlock(iter, level + 1);
848 if (PTR_ERR_OR_ZERO(ret) == -EINTR)
849 bch2_btree_iter_upgrade(iter, level + 2);
851 BUG_ON(!IS_ERR(ret) && !btree_node_locked(iter, level));
853 if (!IS_ERR_OR_NULL(ret)) {
854 struct btree *n1 = ret, *n2 = b;
856 if (sib != btree_prev_sib)
859 BUG_ON(bkey_cmp(btree_type_successor(n1->btree_id,
864 bch2_btree_trans_verify_locks(trans);
869 void bch2_btree_node_prefetch(struct bch_fs *c, struct btree_iter *iter,
870 const struct bkey_i *k, unsigned level)
872 struct btree_cache *bc = &c->btree_cache;
875 BUG_ON(!btree_node_locked(iter, level + 1));
876 BUG_ON(level >= BTREE_MAX_DEPTH);
878 b = btree_cache_find(bc, k);
882 bch2_btree_node_fill(c, iter, k, level, SIX_LOCK_read, false);
885 void bch2_btree_node_to_text(struct printbuf *out, struct bch_fs *c,
888 const struct bkey_format *f = &b->format;
889 struct bset_stats stats;
891 memset(&stats, 0, sizeof(stats));
893 bch2_btree_keys_stats(b, &stats);
896 "l %u %llu:%llu - %llu:%llu:\n"
899 b->data->min_key.inode,
900 b->data->min_key.offset,
901 b->data->max_key.inode,
902 b->data->max_key.offset);
903 bch2_val_to_text(out, c, bkey_i_to_s_c(&b->key));
905 " format: u64s %u fields %u %u %u %u %u\n"
906 " unpack fn len: %u\n"
907 " bytes used %zu/%zu (%zu%% full)\n"
908 " sib u64s: %u, %u (merge threshold %zu)\n"
909 " nr packed keys %u\n"
910 " nr unpacked keys %u\n"
912 " failed unpacked %zu\n"
914 " failed overflow %zu\n",
916 f->bits_per_field[0],
917 f->bits_per_field[1],
918 f->bits_per_field[2],
919 f->bits_per_field[3],
920 f->bits_per_field[4],
922 b->nr.live_u64s * sizeof(u64),
923 btree_bytes(c) - sizeof(struct btree_node),
924 b->nr.live_u64s * 100 / btree_max_u64s(c),
927 BTREE_FOREGROUND_MERGE_THRESHOLD(c),
931 stats.failed_unpacked,
933 stats.failed_overflow);