Before the introduction of PQ_LAUNDRY, "pass" controlled how aggressively we laundered pages. Now, it really serves little purpose: If the page daemon wakes up because of a timeout, then we do not even look at the number of free pages. We only scan the active queue.
With the elimination of "pass", I want to point out that the page daemon will attempt to bring the number of free pages up to the target no matter how it was awakened. I do not think that that is a bad idea.