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SubjectRe: 2.4 MM overview?
Date
Andi Kleen writes:
> On Sun, Oct 15, 2000 at 05:29:46PM +0100, Kenn Humborg wrote:
> > <Surprise!>
> >
> > __pa() and __va() are still defined as addr -/+ PAGE_OFFSET. So
> > where did I hear about 2.4 not mapping all memory? Could it be
> > that this applies only to "high memory" in x86?
>
> It only applies to high memory. To access it you have to use kmap().
> To use __pa you need to create a bounce buffer in lowmem first as of 2.4.

PAGE_OFFSET is not the difference between the physical address and the
virtual address; it is defined as the start address of the direct mapped
memory region where the kernel resides. ie, it is an absolute virtual
address. (See previous discussions on this mailing list).

It should probably be renamed in v2.5 so that it no longer implies that
it is an "_OFFSET" of anything.
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