From: Available software

- CRL is a simple all-software distributed shared memory system
  intended for use on message-passing multicomputers and distributed
  systems.  CRL 1.0 can be compiled for use on the MIT Alewife
  Machine, Thinking Machine's CM-5, and networks of Sun workstations
  running SunOS 4.1.3 communicating with one another using TCP and
  PVM.  Because CRL requires no functionality from the underlying
  hardware, compiler, or operating system beyond that necessary to
  send and receive messages, porting CRL to other platforms should
  prove to be straightforward.

  General information about CRL can be found at
  <URL:http://www.pdos.lcs.mit.edu/crl>.  The CRL 1.0 source
  distribution (sources for CRL 1.0 and several applications, user
  documentation, and a postscript version of a paper about CRL to
  appear in this SOSP later this year) is available at
  <URL:http://www.pdos.lcs.mit.edu/crl/source.html>.

- Ron Minnich <rminnich@earth.sarnoff.com> has implemented a
  distributed shared memory system called MNFS, which is a modified
  version of NFS and runs alongside NFS in the kernel.

  Performance is good; page faults under FreeBSD 2.0R run at about the
  same speed as NFS (~5.9 milliseconds per page).  If you need to
  update a page from one host to many clients, it can be done at a
  cost of 1.2 milliseconds or so per client.  This scales: networks of
  128 nodes running MNFS have been set up, and times should improve
  over faster LANs than Ethernet.

  The MNFS programming model uses mmap'ed files.  Programs map files
  in and then use them as ordinary memory.  Cache consistency of a
  page is maintained by the MNFS servers, ensuring that there is only
  one writeable copy in the network at a time.  The model is not
  strongly coherent; read-only copies of a page are only refreshed by
  an explicit action on the part of the holder of a writeable page
  (using msync).  For those who don't like this style of programming,
  a parallel C compiler has been retargeted to use MNFS on clusters
  and networks of computers running Condor.  Both performance and
  scalability matched explicitly mmap-coded systems.

  The system has been implemented on Sunos 4.1.x, Solaris 2.2 and 2.3,
  IRIX 5.2 and 5.3, and AIX 3.2.  All of these were legally
  encumbered, so the FreeBSD version is currently the only
  freely-available implementation.

  MNFS is available from <URL:ftp:ftp.sarnoff.com/pub/mnfs>, and may be
  installed either as a set of diffs to the FreeBSD 2.0.5R kernel, or
  installed in-place.  Also included in this directory is a slightly
  out-of-date paper on MNFS, and a more current manual.

  A Linux port of MNFS is in the works.