mm: vmscan: remove remains of kswapd-managed zone->all_unreclaimable

mm: vmscan: remove remains of kswapd-managed zone->all_unreclaimable

shrink_zones() has a special branch to skip the all_unreclaimable() check
during hibernation, because a frozen kswapd can't mark a zone
unreclaimable.

But ever since 6e543d5780e3 ("mm: vmscan: fix do_try_to_free_pages()
livelock"), determining a zone to be unreclaimable is done by directly
looking at its scan history and no longer relies on kswapd setting the
per-zone flag.

Remove this branch and let shrink_zones() check the reclaimability of the
target zones regardless of hibernation state.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: KOSAKI Motohiro <Kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>