Re: OT: down with memory protection!
From: Kirk Strauser (kirk_at_strauser.com)
Date: 12/02/04
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To: debian-user@lists.debian.org Date: Thu, 2 Dec 2004 15:38:38 -0600
On Thursday 02 December 2004 09:30, Sam Watkins wrote:
> Current mainstream OSes like Linux implement memory protection primarily
> to prevent buggy or malicious processes trampling on each-others memory
> and memory-mapped devices, or spying on other processes.
No, they don't. Memory protection is generally a free side effect of
virtual memory (not to be confused with "swap"). That is, virtual memory
is the goal, and memory protection is a good thing that comes along with
it.
> All processes could run on a single address space, there would be no need
> for context-switching, pipes could be implemented as shared buffers, and
> processes could send messages to eachother without needing to copy
> memory.
Congratulations - you've just invented shared memory (see shm*(2) for
details on the Linux syscalls that implement it).
> I think people don't normally use more than 4GB of VM on 32-bit
> computers, at least they won't now that 64 bit CPUs are taking off,
Not even close to correct, actually.
> Programs could call "yield" every now and again,
Get a pre-OS X Macintosh and see how well you like it. Seriously, it's
called cooperative multitasking, and it's generally not well-regarded.
> and the compiler and programmer could be required to prove that the code
> would not loop forever without calling yield.
This is provably impossible. Reference "the halting problem".
> Files could be accessed by partially mapping them to memory.
See "man 2 mmap" for details.
> Anyway, if anyone would comment on any of this vapourware, I'd like to
> hear it - off the list if you think it's too off topic.
Sorry, but your ideas have pretty much already been implemented (and in some
cases discarded). :-/
-- Kirk Strauser
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