Some issues for single address space systems
Chase, J.; Feeley, M.; Levy, H.
Workstation Operating Systems, 1993. Proceedings., Fourth Workshop on
Volume , Issue , 14-15 Oct 1993 Page(s):150 - 154
Digital Object Identifier 10.1109/WWOS.1993.348157
Summary:We previously described Opal, an OS environment that has a single
virtual address space common to all protection domains, rather than the
usual private virtual address space per protection domain (e.g., a Unix
process). All threads on an Opal node see the same mapping of virtual to
physical addresses; any thread can reference any virtual address, but
access to the data is determined by the thread's protection domain. The
single address space approach is made feasible by the large virtual
address spaces of the newest RISC processors. It allows protection
domains to pass and share memory segments by mutual consent, while
preserving the meaning of pointers. At the time Opal was a paper design,
with only a few pieces of implementation. Since that time the key
features of Opal have been prototyped. While the current prototype runs
on 32-bit MIPS systems, it demonstrates that the model is both workable
and useful. Yet the single address space idea remains a difficult
adjustment, both conceptually and practically, for those of us long
accustomed to per-process address spaces. Having spent much of the past
year arguing the benefits of the model, our purpose now is to outline
some of its limitations and complications. The goal is to separate the
real problems from the false ones, and to focus the debate on the areas
that we think are most important, based on our experience
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