21 Dec
2022
21 Dec
'22
5:18 a.m.
On Dec 20, 2022, at 2:25 PM, Noel Chiappa
<jnc(a)mercury.lcs.mit.edu> wrote:
You are right! Mea culpa.
There is a further para:
Like the UNIX system for the PDP-11, the current
implementation for the VAX-11/780 maintains each process
in contiguous physical memory and swaps processes to disk
when there is not enough physical memory to contain them
all. Reducing external memory fragmentation to zero by
utilizing the VAX- 11/780 memory mapping hardware for
scatter loading is high on the list of things to do in
the second imple- mentation pass. To simplify kernel
memory allocation, the size of the user-segment memory
map is an assembly parameter which currently allows three
pages of page table or 192K bytes total for text, data,
and stack. This also deserves to be rewritten, both to
allow varying process size, and to allow processes larger
than physical memory through demand paging. Dynamic page
table size would mean dynamic u area size if the page
table remained part of the u area.
This seems like a minimal "bring up" port of V7. Later they
must have implemented demand paging?
From: Bakul Shah
Is there a publicly available description of
Reiser's VM system? I
found "A Unix operating system for the DEC VAX 11/780 Computer" by
London & Reiser which includes a long paragraph on VM (included below)
That para is basically all about the VAX paging hardware; it doesn't say
anything about how that (any :-) Unix actually uses it.