Re: Question on mmap() in 64-bit OS

On Tue, 27 Nov 2007 02:35:27 +0800 LaBird <b_cheung_2005@xxxxxxxxx> wrote:

| Many thanks for your answer. I didn't realize only 48 bits are supported for
| addressing in most 64-bit dual-core systems. I think it's the same case for
| my friend's dual-core Pentium in office and my dual-core Athlon.

Come the day we actually need more than 48-bit addresses, there will also
be a lot of structural changes, primarily affecting the kernel and how it
handles things like virtual memory and simultaneous views of kernel space
and user space (things are a whole lot easier if the kernel can at least
have the whole kernel space and one whole VM in its view at once). Given
that a lot of the real address space is highly structured (similar to how
the way-over-addressed 128-bit IPv6 network address space is done), we are
likely to see limitations hit before we ever see a 63-bit address VM. Do
not count out 128-bit machines in the next decade or so, even though we
probably will not have achieved any kind of storage device with 2^64 bytes
of memory that would need it. It's more about structure. A 64-bit design
I made a couple dacades ago was itself highly structured, although it did
provide for 2^56 bytes of VM, 2^56 bytes of kernel space. All the rest
was divided up into system control and I/O in a CPU agnostic scheme.

--
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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