mm: don't wait on congested zones in balance_pgdat()

mm: don't wait on congested zones in balance_pgdat()

Commit 92df3a72 (mm: vmscan: throttle reclaim if encountering too many
dirty pages under writeback) introduced waiting on congested zones
based on a sane algorithm in shrink_inactive_list(). What this means
is that there's no more need for throttling and additional heuristics
in balance_pgdat(). So, let's remove it and tidy up the code.

Signed-off-by: Zlatko Calusic <zlatko.calusic@iskon.hr>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>