Re: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]

[Andrea Arcangeli]

On Mon, May 06, 2002 at 03:07:07AM +0200, Daniel Phillips wrote:
> On Monday 06 May 2002 02:55, Russell King wrote:
> > On Mon, May 06, 2002 at 01:54:52AM +0200, 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.
> > 
> > I see no problem with the above with the existing discontigmem stuff.
> > discontigmem does *not* require a linear relationship between kernel
> > virtual and physical memory.  I've been running kernels for a while
> > on such systems.
> 
> Look, you've got this:
> 
> #define __phys_to_virt(ppage) ((unsigned long)(ppage) + PAGE_OFFSET - PHYS_OFFSET)
> 
> So, since __phys_to_virt (and hence phys_to_virt and __va) is clearly linear, the
> relation __pa(__va(kva)) == kva cannot hold.  Perhaps that doesn't bother you?

Check my previous email:

	[..] They will all be normal zones provided you implement a static
	view of them in the kernel virtual address space, and you also
	cover page_address/virt_to_page [..]

Depending on the kind of coalescing of those chunks in the direct
mapping virt_to_page/page_address will vary. virt_to_page and
page_address will have all the necessary internal knowledge in order to
make it all zone_normal.

Andrea