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authorNeal H. Walfield <neal@gnu.org>2008-12-09 14:21:49 +0100
committerNeal H. Walfield <neal@gnu.org>2008-12-09 14:21:49 +0100
commit353c141d37fccd5373f06e0c2aa19b0f947df0bb (patch)
tree512d363a7c8551a8454f51dd6d7b363fe027b1cc /microkernel/viengoos
parent82537d62d88b592547de36ad7bec392199ee8ade (diff)
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@@ -24,6 +24,37 @@ corresponding to a frame, which is keyed on its physical address.
# Major
+## Address Space Management
+
+In Viengoos, a process's address space is managed entirely in user
+space by the process itself. This creates two interesting problems:
+dealing with circular dependencies resulting from having to manage the
+address space data structures and accessing and manipulating the
+address space data structures.
+
+First, managing the address space requires resources, which in turn
+may require address space (e.g., data structures require memory which
+require address space, etc.). We currently break this circular
+dependency by trying to keep enough resources in reserve that
+allocating resources for managing the address space never requires
+more resources than are minimally in the reserve. The reserve is
+currently chosen in an ad-hoc fashion. It would be nice to determine
+it more systematically. Moreover, it would be nice to reduce the
+cases in which a reserve is required. This may be possible by
+restructuring some of the code.
+
+Second, the address space data structures are protected using a single
+lock. This not only means that only a single thread can be updating
+the address space at a time, but that if a thread faults and the
+address space is locked, then the process dead locks! It should be
+possible to at least walk the address space using lock-free
+techniques. This requires updating the address space construction
+code such that all addresses remain valid during any given
+manipulation. Second, to avoid the mentioned dead-lock problem, we
+try to ensure that accessing the data structures will never result in
+a fault. This means protecting the stack. An alternative approach is
+to use undo buffers.
+
# Thesis
## Capability aware compiler