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> In general a address in a process is just a linear address which refer to
> physical address indirectly by page directory. This is reasonable in
> user space. However is it necessary to do such thing in kernel? It is sure
> to have penalty when converting a linear address to physical thing. Is it
> worth doing such thing in kernel.
No. Turning paging on/off is expensive on x86, and you can't do it
easily in some important cases.
> I think the performance is the most
> important in kernel, other thing is second. I remember in linux linear
> address is real physical address in kernel space(is it true?). Why freebsd
> does not do in the same way?
Identity-mapping virtual:physical addresses is not the same as disabling
paging. Linux, like all other sane x86 protected-mode operating systems
leaves paging enabled.
--
... every activity meets with opposition, everyone who acts has his
rivals and unfortunately opponents also. But not because people want
to be opponents, rather because the tasks and relationships force
people to take different points of view. [Dr. Fritz Todt]
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