Steps to reproduce:
1) Disable SWAP (in case you have it and to simplify testing)
2) Have some of your RAM taken by running heavy applications (Firefox/Chrome/IDEs/etc.)
3) Create a file in TMPFS > $free_available_ram
4) See your userspace die
I'm curious why in this situation the kernel starts doing _massive_ amounts of disk IO - I don't even understand what's being read or written since SWAP is disabled, and all applications are in RAM doing pretty much nothing.
Also for some reasons OOM doesn't kick in and the only way to unfreeze your PC is to forcefully reboot it or to continuously press SysRq + F until enough applications get killed.