There are two functions to flush the per-cpu data of an lruvec into the
rest of the cgroup tree: when the cgroup is being freed, and when a CPU
disappears during hotplug.  The difference is whether all CPUs or just
one is being collected, but the rest of the flushing code is the same.
Merge them into one function and share the common code.

Link: https://lkml.kernel.org/r/20210209163304.77088-8-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NRoman Gushchin <guro@fb.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>