mm/memory_hotplug: use helper zone_is_zone_device() to simplify the code

Patch series "Cleanup and fixups for memory hotplug".

This series contains cleanup to use helper function to simplify the code.
Also we fix some potential bugs.  More details can be found in the
respective changelogs.

This patch (of 3):

Use helper zone_is_zone_device() to simplify the code and remove some
explicit CONFIG_ZONE_DEVICE codes.

Link: https://lkml.kernel.org/r/20210821094246.10149-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210821094246.10149-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Chris Goldsworthy <cgoldswo@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -477,15 +477,13 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
 				 sizeof(struct page) * cur_nr_pages);
 	}
 
-#ifdef CONFIG_ZONE_DEVICE
 	/*
 	 * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
 	 * we will not try to shrink the zones - which is okay as
 	 * set_zone_contiguous() cannot deal with ZONE_DEVICE either way.
 	 */
-	if (zone_idx(zone) == ZONE_DEVICE)
+	if (zone_is_zone_device(zone))
 		return;
-#endif
 
 	clear_zone_contiguous(zone);