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SubjectRe: Linux and physical memory
On Sun, Jan 17, 1999 at 02:44:37PM +0100, Max wrote:
>
> Maybe I am stupid, but while I understand this is correct (i.e. reserve a part
> of processes address space to point to kernel code/data), I don't
> understand why the kernel needs to always have all physical memory mapped
> in its address space.

Because you perform a syscall, say for I/O, and tell the kernel: Hey, put
this into this buffer. Now, what woul the kernel do, if the memory is not
mapped? How should the kernel start a binary, if it can not access the
memory, where it's started.
If the kernel does not map the memory, it cannot control it.
The only way out is to use other selectors and to have context switches,
which would hurt performance, as said before.
I don't think, that's what we want.

--
Kurt Garloff <kurt@garloff.de> [Dortmund, FRG]
Plasma physics, high perf. computing [Linux-ix86,-axp, DUX]
PGP key on http://www.garloff.de/kurt/ [Linux SCSI driver: DC390]

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