mm: vmscan: naming fixes: global_reclaim() and sane_reclaim()

Seven years after introducing the global_reclaim() function, I still have
to double take when reading a callsite.  I don't know how others do it,
this is a terrible name.

Invert the meaning and rename it to cgroup_reclaim().

[ After all, "global reclaim" is just regular reclaim invoked from the
  page allocator. It's reclaim on behalf of a cgroup limit that is a
  special case of reclaim, and should be explicit - not the reverse. ]

sane_reclaim() isn't very descriptive either: it tests whether we can use
the regular writeback throttling - available during regular page reclaim
or cgroup2 limit reclaim - or need to use the broken
wait_on_page_writeback() method.  Use "writeback_throttling_sane()".

Link: http://lkml.kernel.org/r/20191022144803.302233-5-hannes@cmpxchg.org


Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>