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

On Thu, 29 Nov 2007 12:44:57 +0800 LaBird <b_cheung_2005@xxxxxxxxx> wrote:
| Hi Phil,
|
| <phil-news-nospam@xxxxxxxx> wrote:
|>
|> 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
|
| I agree with you. Perhaps with a large address space, the process space
| should be a global one for all processes in execution, rather than each
| process having its own process space.

Sounds like Multics.

However, I don't agree that there is any significant benefit to this.
While 48-bits does provide sufficient address space to do that, I think
it is a bad idea to do so just because it can be done.

There _could_ be some value in allowing the _kernel_ to view TWO virtual
address spaces simultaneously: eliminate extra copying or extra context
switching to copy between VMs.


| On the other hand, in the hardware aspect, there may be a need for some
| alternative large secondary storage which is much faster than hard disks.
| Otherwise a large VM may not be really useful as executing applications with
| large VM/RAM demand will not be practical.

Get more RAM. If you have an application that uses a LOT of RAM, get a LOT.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-11-29-0830@xxxxxxxx |
|------------------------------------/-------------------------------------|
.

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