Other lock order is following:
PG_locked.
mm->page_table_lock
- zone_lru_lock
+ pgdat->lru_lock
lock_page_cgroup.
In many cases, just lock_page_cgroup() is called.
per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
- zone_lru_lock, it has no lock of its own.
+ pgdat->lru_lock, it has no lock of its own.
2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)