> I don't think I've ever encountered a machine that used so much memory that the kernel didn't have buffers, but not so much that it invoked OOM killer.

Note that the reason this topic is currently in vogue is that this has become a lot easier recently. If you run the system on a modern low-latency SSD, the current OOM killer algorithm often fails to kill anything before the entire system is on it's knees with approximately 0 pages left for IO and non-anonymous memory, at which point the OOM killer will never run because the machine is so thoroughly locked. The proper way to fix this of course is to make the OOM killer hit earlier.