Revert "mm/vmstat.c: do not show lowmem reserve protection information of empty zone"

This reverts commit 26e7dead.

Sonny reported that one of their tests started failing on the latest
kernel on their Chrome OS platform.  The root cause is that the above
commit removed the protection line of empty zone, while the parser used in
the test relies on the protection line to mark the end of each zone.

Let's revert it to avoid breaking userspace testing or applications.

Fixes: 26e7dead ("mm/vmstat.c: do not show lowmem reserve protection information of empty zone)"
Reported-by: Sonny Rao <sonnyrao@chromium.org>
Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>	[5.8.x]
Link: http://lkml.kernel.org/r/20200811075412.12872-1-bhe@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmstat.c

@@ -1642,12 +1642,6 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   zone->present_pages,
 		   zone_managed_pages(zone));
 
-	/* If unpopulated, no other information is useful */
-	if (!populated_zone(zone)) {
-		seq_putc(m, '\n');
-		return;
-	}
-
 	seq_printf(m,
 		   "\n        protection: (%ld",
 		   zone->lowmem_reserve[0]);
@@ -1655,6 +1649,12 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
 	seq_putc(m, ')');
 
+	/* If unpopulated, no other information is useful */
+	if (!populated_zone(zone)) {
+		seq_putc(m, '\n');
+		return;
+	}
+
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
 		seq_printf(m, "\n      %-12s %lu", zone_stat_name(i),
 			   zone_page_state(zone, i));