- It is allowed to mount a directory on a non-directory.

- When a non-directory is mounted the root inode is not filled in, only at
  the first getattr

- I want really low priority for my cached pages.  Can they start out
  'old' so they will be thrown out on the first oportunity?

- File size change could cause some strange behavior WRT the page
  cache.

- User can cause nasty DoS by not replying to WRITE requests and thus
  blocking writepage() indefinitely.