em_cgroup_force_empty which is triggered only by userspace (mem_cgroup_force_empty_write) or when a cgroup is removed (mem_cgroup_pre_destroy). Although these are not usually frequent operations it still makes some sense to do targeted draining as well, especially if the box has many CPUs. This patch unifies both methods to use the single code (drain_all_stock) which relies on the original async implementation and just adds flush_work to wait on all caches that are still under work for the sync mode. We are using FLUSHING_CACHED_CHARGE bit check to prevent from waiting on a work that we haven't triggered. Please note that both sync and async functions are currently protected by percpu_charge_mutex so we cannot race with other drainers. Signed-off-by: Michal Hocko Reviewed-by: KAMEZAWA Hiroyuki Cc: Balbir Singh Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds