When a cluster is very busy, scheduling opportunities are few and far between. Scheduling opportunities are how an application knows when to give up looking for decent locality.
It doesn't make sense to work hard waiting for locality when the odds of it coming are very small and it may actually take a very long time to actually give up.
This causes the priority of queues to be violated which is the last thing we want to do when the cluster is full.
Add a mode to disable skipping locality when cluster is busy.