I vaguely remember reading somewhere that they figured out a way to run their collector on stock Linux; I think the price they paid in exchange was (even) lower throughput (trying to track down reference so I know I wasn't daydreaming) (yes, I daydream about GCs).

A while ago, I read through the kernel patch they provided, and it was basically adding batch APIs for mremap so you don't have to have a TLB flush for every call. Also because all mutator threads needed to be paused at a safepoint while the remaps happen, so the batch API has much shorter pause time.