speed up mount/umount
Currently all mounts are managed in a linked list. On mount and umount, this list has to be searched sequentially. If the system has many mounts (e.g. > 10000), this takes a significant amount of time. The time to mount / umount grows quadratically with number of mounts.
This should be sped up by organizing the mounts also into two avl trees, one indexed by mountpoint and one indexed by dev.