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SubjectRe: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]
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On Monday 06 May 2002 10:54, Roman Zippel wrote:
> Hi,
>
> On Mon, 6 May 2002, Daniel Phillips wrote:
>
> > I must be guilty of not explaining clearly. Suppose you have the following
> > physical memory map:
> >
> > 0: 128 MB
> > 8000,0000: 128 MB
> > 1,0000,0000: 128 MB
> > 1,8000,0000: 128 MB
> > 2,0000,0000: 128 MB
> > 2,8000,0000: 128 MB
> > 3,0000,0000: 128 MB
> > 3,8000,0000: 128 MB
> >
> > The total is 1 GB of installed ram. Yet the kernel's 1G virtual space,
> > can only handle 128 MB of it. The rest falls out of the addressable range and
> > has to be handled as highmem, that is if you preserve the linear relationship
> > between kernel virtual memory and physical memory, as config_discontigmem does.
> > Even if you go to 2G of kernel memory (restricting user space to 2G of virtual)
> > you can only handle 256 MB.
>
> Why do you want to preserve the linear relationship between virtual and
> physical memory?

I don't, I observed that in all known instances of config_discontigmem, that
linear relationship is preserved. Now, you and Andrea are suggesting that no
such linear relation is strictly necessary and I believe its worth investigating
further, to see how it would work and how it compares to config_nonlinear.

> There is little common code (and only during
> initialization), which assumes a direct mapping. I can send you the
> patches to fix this.

I already have patches to do that, that is, config_nonlinear. I'm interested in
looking at your patches though, because we might as well give all the different
approaches a fair examination.

> Then you can map as much physical memory as you want
> into a single virtual area and you only need a single pgdat.

You're talking about your 68K solution with the loops that search through
memory regions? If so, I've already looked at it and understand it. Or, if
it's a new approach, then naturally I'd be interested.

--
Daniel
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