Add memory-efficient snapshots to tmpfs. A snapshot is a view of the filesystem, frozen at a particular point in time. The snapshotted filesystem is not frozen, only the view is. That is, you can continue to read/write/create/delete files in the snapshotted filesystem.

The interface to snapshots may resemble the interface to null mounts, e.g., 'mount -t snapshot /var/db /db-snapshot' makes a snapshot of /var/db/ at /db-snapshot/.

You should exploit features of the virtual memory system like copy-on-write memory pages to lazily make copies of files that appear both in a live tmpfs and a snapshot. This will help conserve memory.