> 
> MFS works by having a program, mount_mfs, allocate a Really Big Chunk
> of memory.  That process, and its memory space, sticks around for the
> entire time that MFS is.  MFS reads and writes data via copyin from
> and copyout to the process's address space.  (I'm sure it _could_ be
> made more inefficient, but i'm not going to try...  8-)
> 
One minor clarification -- MFS allocates VIRTUAL MEMORY, or normal
process memory space.  So, that space is backed by swap, and can
(with dubious effects) be paged out.  You really want to avoid
paging your MFS, but it can/will be under tight memory conditions.

Actually, I think of the paged MFS as having an advantage over a pure
ramdisk (that takes up wired memory all of the time.)  When memory
does get tight, that allocated space for metadata, and unused files
is pushed out to swap space...  The key is to NOT take advantange
of its pageability to excess.

John
dyson@freebsd.org