mm/migrate.c: no need to check for i > start in do_pages_move()

Patch series "cleanup on do_pages_move()", v5.

The logic in do_pages_move() is a little mess for audience to read and has
some potential error on handling the return value. Especially there are
three calls on do_move_pages_to_node() and store_status() with almost the
same form.

This patch set tries to make the code a little friendly for audience by
consolidate the calls.

This patch (of 4):

At this point, we always have i >= start.  If i == start, store_status()
will return 0.  So we can drop the check for i > start.

[david@redhat.com rephrase changelog]
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Link: http://lkml.kernel.org/r/20200214003017.25558-2-richardw.yang@linux.intel.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -1694,11 +1694,9 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
 				err += nr_pages - i - 1;
 			goto out;
 		}
-		if (i > start) {
-			err = store_status(status, start, current_node, i - start);
-			if (err)
-				goto out;
-		}
+		err = store_status(status, start, current_node, i - start);
+		if (err)
+			goto out;
 		current_node = NUMA_NO_NODE;
 	}
 out_flush: