Re: Architecture of Backing Store Descriptors Jonathan Shapiro (shap@viper.cis.upenn.edu)
Tue, 22 Nov 94 21:23:15 -0500

(Are processes in traditional Unix systems useless just
because they aren't persistent?)

No. They're useless because they are on traditional Unix systems...

Well, if composition _is_ supported as a fundamental abstraction (and I think it should be), there is no reason for a NewSys address space _not_ to be simply a simple segment, which will presumably always be a composition of other segments or mappings.

I think there is. The problem with assignment of fault responsibility is serious. One wants to be able to make a clear distinction between a fault in the object and a fault in the mapping. Segments make that distinction impossible. If memory objects nest, the assignment of the proper scope to a fault becomes ambiguous very quickly.

In addition, the usual case is large contiguous mappings of dense objects. Tree structures don't do this well.

Can you be a little more specific about how you intend to use composable memory objects and why the existing model in Mach is inadequate for what you need (other than the implementation)?

Jonathan