memcg: get rid of once-per-second cache shrinking for dead memcgs

memcg: get rid of once-per-second cache shrinking for dead memcgs

The idea is to synchronously do it, leaving it up to the shrinking
facilities in vmscan.c and/or others.  Not actively retrying shrinking may
leave the caches alive for more time, but it will remove the ugly wakeups.
 One would argue that if the caches have free objects but are not being
shrunk, it is because we don't need that memory yet.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>