We're seeing OOM kills from fork(), which requires 4 contiguous pages (order 2), with plenty of available RAM and swap, but with RAM too fragmented to satisfy the request.

We tried turning it on already but it correlated with a couple of problems.  See issue 603594 (April 2016) where we reverted the turn-ons.  It's also possible that issue 585552 is related to compaction.  Finally,  issue 586052  also involves compaction but only in 3.8 kernels.  The highest interest at this time is 3.18.