Commit a592cdf5 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

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



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: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 3e878fe5

fs/bcachefs/btree_key_cache.c

+27 −3
Original line number Diff line number Diff line
@@ -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();

	}