Mill Computing, Inc. Forums The Mill Architecture Inter-process Communication Reply To: Inter-process Communication

Ivan Godard
Keymaster
Post count: 627

There’s two kinds of potential fragmentation: of the physical memory space, and of the virtual address space. They are tied in a legacy architecture, but separated on a Mill. The physical space is managed by the TLB, which can do paging and physical consolidation in a manner very similar to a legacy. In contrast, the virtual space is never consolidated; this is a consequence of the fundamental design choice to have caches in virtual.

There’s no obvious advantages to having a 32-bit virtual space in a 60-bit physical space. True, pointers would be four bytes rather than eight, but one can use 32-bit indices just as easily. There’s the problem of programs that need more than 4G, but those could use large mode. But the big problem is mixed mode. Sandbox code will need to use facilities from outside the sandbox, and those would be reached by 8-byte addresses. Keeping track of near-vs.-far addresses is something that we left behind with the 8086.

So yours is an interesting question: could it be done in the hardware? I think the answer is yes, the hardware could do it. But it would cause a great gnashing of teeth, both among our software teams and customers that used it. Would it sell enough more chips to justify the pain? I don’t think so.