bcachefs: Enable automatic shrinking for rhashtables

Since the key cache shrinker walks the rhashtable, a mostly empty
rhashtable leads to really nasty reclaim performance issues.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_cache.c

@@ -95,6 +95,7 @@ static const struct rhashtable_params bch_btree_cache_params = {
 	.key_offset		= offsetof(struct btree, hash_val),
 	.key_len		= sizeof(u64),
 	.obj_cmpfn		= bch2_btree_cache_cmp_fn,
+	.automatic_shrinking	= true,
 };
 
 static int btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)

fs/bcachefs/btree_key_cache.c

@@ -36,6 +36,7 @@ static const struct rhashtable_params bch2_btree_key_cache_params = {
 	.key_offset		= offsetof(struct bkey_cached, key),
 	.key_len		= sizeof(struct bkey_cached_key),
 	.obj_cmpfn		= bch2_btree_key_cache_cmp_fn,
+	.automatic_shrinking	= true,
 };
 
 __flatten

fs/bcachefs/io_read.c

@@ -87,6 +87,7 @@ static const struct rhashtable_params bch_promote_params = {
 	.head_offset		= offsetof(struct promote_op, hash),
 	.key_offset		= offsetof(struct promote_op, pos),
 	.key_len		= sizeof(struct bpos),
+	.automatic_shrinking	= true,
 };
 
 static inline int should_promote(struct bch_fs *c, struct bkey_s_c k,

fs/bcachefs/movinggc.c

@@ -38,6 +38,7 @@ static const struct rhashtable_params bch_move_bucket_params = {
 	.head_offset		= offsetof(struct move_bucket_in_flight, hash),
 	.key_offset		= offsetof(struct move_bucket_in_flight, bucket.k),
 	.key_len		= sizeof(struct move_bucket_key),
+	.automatic_shrinking	= true,
 };
 
 static struct move_bucket_in_flight *