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bcachefs: don't use rht_bucket() in btree_key_cache_scan()

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rht_bucket() does strange complicated things when a rehash is in
progress.

Instead, just skip scanning when a rehash is in progress: scanning is
going to be more expensive (many more empty slots to cover), and some
sort of infinite loop is being observed

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-08-19 16:41:00 -04:00
parent 3e878fe5a0
commit a592cdf516
1 changed files with 27 additions and 3 deletions
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30
fs/bcachefs/btree_key_cache.c
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@ -778,6 +778,20 @@ static unsigned long bch2_btree_key_cache_scan(struct shrinker *shrink,
rcu_read_lock();
tbl = rht_dereference_rcu(bc->table.tbl, &bc->table);
/*
* Scanning is expensive while a rehash is in progress - most elements
* will be on the new hashtable, if it's in progress
*
* A rehash could still start while we're scanning - that's ok, we'll
* still see most elements.
*/
if (unlikely(tbl->nest)) {
rcu_read_unlock();
srcu_read_unlock(&c->btree_trans_barrier, srcu_idx);
return SHRINK_STOP;
}
if (bc->shrink_iter >= tbl->size)
bc->shrink_iter = 0;
start = bc->shrink_iter;
@ -785,7 +799,7 @@ static unsigned long bch2_btree_key_cache_scan(struct shrinker *shrink,
do {
struct rhash_head *pos, *next;
pos = rht_ptr_rcu(rht_bucket(tbl, bc->shrink_iter));
pos = rht_ptr_rcu(&tbl->buckets[bc->shrink_iter]);
while (!rht_is_a_nulls(pos)) {
next = rht_dereference_bucket_rcu(pos->next, tbl, bc->shrink_iter);
@ -866,12 +880,22 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
while (atomic_long_read(&bc->nr_keys)) {
rcu_read_lock();
tbl = rht_dereference_rcu(bc->table.tbl, &bc->table);
if (tbl)
if (tbl) {
if (tbl->nest) {
/* wait for in progress rehash */
rcu_read_unlock();
mutex_lock(&bc->table.mutex);
mutex_unlock(&bc->table.mutex);
rcu_read_lock();
continue;
}
for (i = 0; i < tbl->size; i++)
rht_for_each_entry_rcu(ck, pos, tbl, i, hash) {
while (pos = rht_ptr_rcu(&tbl->buckets[i]), !rht_is_a_nulls(pos)) {
ck = container_of(pos, struct bkey_cached, hash);
bkey_cached_evict(bc, ck);
list_add(&ck->list, &items);
}
}
rcu_read_unlock();
}