[TUHS] Memory management in Dennis Ritchie's C Compiler
paul.winalski at gmail.com
Tue Aug 18 05:50:29 AEST 2020
On 8/17/20, Larry McVoy <lm at mcvoy.com> wrote:
> On Mon, Aug 17, 2020 at 03:27:15PM -0400, Noel Chiappa wrote:
> Bill Joy imagined it, the prototype is in one the 4.x BSD releases.
> Sun (Joe Moran) actually implemented it first in any Unix variant.
> It's possible the concept existed in some other OS but I'm not aware
> of it.
VAX/VMS had the equivalent of mmap(2) back in 1978. You can specify a
range of contiguous pages in virtual memory and associate that with a
(page-aligned) range of blocks in a file. The blocks in the file act
as backing store for the virtual memory. VMS also has a system call
$CRETVA (create virtual address space) that lets you associate a VA
range using the system page file as backing store. The VMS image
activator (runtime loader in Unix-speak) used these primitives to load
program images into virtual memory. More than one process can map the
same region of a file. This is how sharing of read-only program
segments such as .text is implemented.
I think Burroughs OSes had this concept even before VMS.
There is also $EXPREG (expand address region), which is more or less
equivalent to sbrk().
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