Subject: Re: savecore_flags="-z"
To: Wolfgang Solfrank <>
From: Andrew Brown <>
List: tech-kern
Date: 12/02/1999 16:24:58
>> > of course not, no.  but how can you can address more than 4gb on a 32
>> > bit machine?  really big page tables?
>> yup.
>> While our pmap doesn't support it, recent x86 processors (Pentium Pro
>> and Pentium II) support a page table format extension which allows use
>> of 36-bit physical addresses (although the virtual address space per
>> process is still limited to 32 bits).
>This is totally orthogonal.

it doesn't seem seem to be saying the same thing.

>The question was whether you may get to swap with 4GB on a 32bit machine.
>Of course you can.

okay, i can accept that.  even if i don't understand it.

>The virtual address space of _one_ process (or the kernel for that matter)
>cannot exceed 4GB, as is the case with the physical address space
>(your observation of larger physical address spaces notwithstanding).

sure.  that's easy enough to understand.

>However, there can be more than one process on the machine (and there
>normally _is_ with NetBSD :-)).  And the combined virtual address spaces
>of all process may well exceed 4GB.

this i still don't get, unfortunately most of the experience i have on
paging is "book lernin'"...not much in the way of practical
experience.  if i split a faulted memory access into (according to my
(probably failing) memory) a page table number, a page number, and an
offset within that can i recombine those numbers in some
way (through lookups or what-not) to come up with a number that's
*greater* than 32 bits?  or do we cheat and use bits from the pid or

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