why wal_max_size does not work?

Hello,

We are working on PostgreSQL 10.10. We recently met "no space left".
After checking, the WAL file folder is full.
But we have wal_max_size = 1G configured. I am not that understand why this can happen.
Is this a BUG?

=== LOG ===
## /var/lib/postgresql/data is a network storage with 4G space

pg-0:/var/lib/postgresql/data/pgdata/pg_wal # ls -alh
total 3.9G
drwx------ 3 postgres postgres 20K Mar 21 02:31 .
drwx------ 19 postgres postgres 4.0K Mar 21 02:31 ..
-rw------- 1 postgres postgres 16M Feb 20 14:05

eric-adp-ss7-db-pg-0:/var/lib/postgresql/data/pgdata # du -h -d1
3.9G ./pg_wal
600K ./global
.....
3.9G .

cat postgresql.conf
# Do not edit this file manually!
# It will be overwritten by Patroni!
include 'postgresql.base.conf'

cluster_name = 'eric-adp-ss7-db-pg'
hot_standby = 'on'
listen_addresses = '*'
logging_collector = 'off'
max_connections = '100'
max_locks_per_transaction = '64'
max_prepared_transactions = '0'
max_replication_slots = '10'
max_wal_senders = '10'
max_worker_processes = '8'
port = '5432'
track_commit_timestamp = 'off'
wal_keep_segments = '8'
wal_level = 'replica'
wal_log_hints = 'on'
hba_file = '/var/lib/postgresql/data/pgdata/pg_hba.conf'
ident_file = '/var/lib/postgresql/data/pgdata/pg_ident.conf'

postgres=# SHOW max_wal_size;
max_wal_size
--------------
1GB
(1 row)

BRs,
Fan Liu
ADP Document Database PG