I suspect that when someone did the search and replace when creating
balance_dirty_pages_ratelimited_nr they failed to read the code and
realize this code path was already effectively ratelimited.  The result
is they made it excessively infrequent (every 1MB if ratelimit is 8) in
its calling balance_dirty_pages.

If anyone has ever seen this as an actual problem on a real system, I
would be curious to hear of it.

Hans