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SubjectRe: Linux and physical memory
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Max <max@Linuz.sns.it> writes:
>
> Even if english is not my native language, I thought my question was clear:
>
> >> I don't understand why the kernel needs to always have all physical memory
> >> mapped in its address space.
>
> I said "ALWAYS have mapped ALL physical memory" etc.
>
> So I obviously mean (well, lokkgin to your answer maybe it was not so obvious):
>
> Why can't the kernel just map in its address space the pieces of RAM it needs
> for kernel code/data, and unmap them when done with them?
> User code/data would always be accessible (I am not suggesting to touch user
> processes address space) so I thought that could work and remove the 960MB
> problem.
>
> Maybe that mapping/unmapping of memory in kernel address space is expensive,
> but I don't know. So I posted the question.
>
> Massimiliano Ghilardi

From my understanding of the buffer cache, a buffer can be anywhere in
memory (excluding kernel code and data areas).

And yes, mapping and unmapping is rather expensive because it involves
messing with page tables.

--
Corey Minyard Internet: minyard@acm.org
Work: minyard@nortel.ca UUCP: minyard@wf-rch.cirr.com

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