Page mapping is used as the basis for the whole VM
and much of the I/O subsystem. Its used for shared
libraries, for system5 shared memory and for mmap.
To build a kernel without it is possible, you'd need
to go back to the old disk I/O system, drop the
shared libraries (initially anyway - its in theory
possible to build the shared libraries specially to
use a different segment - not nice though).
You can keep all the protection and stuff as the segmented
architecture still has permissions. You'd end up with a
Linux kernel that needed the VM stuff rewriting, the
paging changed to swapping, and the old style disk I/O
code using. Doable but not trivial
Alan