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SubjectRe: 2.4 MM overview?
On Sun, Oct 15, 2000 at 11:35:23PM +0100, Kenn Humborg wrote:
> On Sun, Oct 15, 2000 at 09:45:11PM +0100, Alan Cox wrote:
> > > Well, we ain't got these luxuries/complications in VAXland... Hell,
> > > we don't even have two-level page tables :-(
> >
> > Really. Ugh. I always assumed Vax had at least two levels because mmap on
> > 4.2 BSD used to panic on 128K+ blocks. I guess there was a different reason
> > for that then
>
> We've kind of got 1.5-level page tables. There are actually 3 page tables.
> The system page table maps memory starting at 0x80000000. The P0 process
> page table maps from 0x0 up and the P1 process page table maps from
> 0x7fffffff down.

And they have to be physically contiguous I guess ?

> This means that sparse address spaces are going to be _really_ expensive
> on PTEs. I don't know how much of a problem this is going to be yet,
> but I'm sure it's going to be fun :-)

512 byte pages, 4 bytes per pte ? Ouch. Can you fill the TLB manually ?

OTOH, I think mapping all physical memory makes sense with the three page
table setup.

Philipp Rumpf
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