On Wed, 11 Aug 1999, Anders Magnusson wrote:

> >
> >   The rtVAX is a variant of the VAX Architecture. An rtVAX processor
> >   implements the per-process page tables in physical memory.  All other
> >   VAX processors implement the per-process page tables in virtual memory.
> >   Therefore, translation of of process-space addresses is different on an
> >   rtVAX than described in Chapter 4. *
> >
> This would require quite much memory in the machine to be useable.
> If the user PTEs must be in physical memory, the memory must be contiguous,
> and therefore it must be allocated at boot. This means that page tables
> for one process of size 32MB would require 256K physical memory, and
> the possibility to have 50 processes would need 12MB pre-allocated memory.
> 
	Would that be the only change needed?

	A variation on that might be to allocate enough space for (say)
	eight user PTEs, then any process that needs to run gets its
	PTEs copied into one of the physical PTEs on a LRU basis. If
	you're using 4K page sizes then presumably the virtual PTEs could
	be 64K each and expand into the 256K physical PTE?

	Its mopre work, but would give a more usable system (unless the
	number of active processes is larger than the number of physical
	PTEs).

	Didn't sun have something similar with hardware contexts on
	the sun4c?

		David/absolute

    -=-  "They're only red from all the thoughts unused inside my head"  -=-