I've had similar problems but no amount of tweaking vm and vfs cache settings helped. Swap or not, both 32gb and 128gb of ram. Manually reclaiming memory would un-lock the system (/sys/fs/cgroup/memory.reclaim).

I wrote a user space memory reclaimer and have not got a lockup since. https://gist.github.com/EBADBEEF/f168458028f684a91148f4d3e79...