Per-file OOM badness

> if the file involved is shared between processes, the memory usage will be divided equally among those processes.

My reading of the patches is that it's divided equally among all file descriptors referencing the file. So e.g. if process A has one file descriptor referencing a file and process B has two file descriptors, process A will be accounted 1/3 of the file's memory, process B 2/3.