I have been doing some experiments using mmap with sbcl-1.0.25-x86-64-linux.
I have been able to sucessfully mmap to files and access the mmapped pages from lisp.

Another thing I would like to do is
create mmapped pages using MAP_ANONYMOUS which are not mapped to files, and the pages initially allow neither read or write access.  I would like
to handle SIGSEGV interrupts to those pages to invoke code to compute the contents of the pages, and then resume the interupted code.

An example use of such a capability is to access large jpeg compressed tiled TIFF images.
A large region of virtual memory is mmapped
using MAP_ANONYMOUS for the uncompressed image tiles (whose size are multiples of the mmap page size).  When a SIGSEGV occurs, the appropriate tile is decompressed from the TIFF image into the uncompressed mmapped tile,
and the PROT_READ is set on those memory pages.

The problem I am having is that SBCL calls SB-SYS:MEMORY-FAULT-ERROR which has no prevision
for invoking a user supplied interrupt-handler or for resuming the code that triggered the SIGSEGV.  Is there any hope not such a capability?