25 Apr
2018
25 Apr
'18
4:02 p.m.
On 25 Apr 2018, at 13:18, Ronald Natalie
<ron(a)ronnatalie.com> wrote:
>
> Early pages were 1K.
Tim Bradshaw <tfb(a)tfeb.org> wrote:
Do systems with huge pages page in the
move-them-to-disk sense I wonder?
I assume they don't in practice because it would be insane but I wonder
if the VM system is in theory even willing to try.
Why not? If there's enough backing store availble?
Note that many systems demand page-in the code section straight out of the
executable, so if some of those pages aren't needed, they can just
be released. And said pages can be shared among all processes running
the same executable, for further savings.
Something I never completely understood in the paging
vs swapping
thing was that I think that systems which could page (well, 4.xBSD in
particular) would *also* swap if pushed. I think the reason for that was
that, if you were really short of memory, swapping freed up the process
structure and also the page tables &c for the process, which would still
be needed even if all its pages had been evicted. Is that right?
It depends upon the system. Some had pageable page tables, which is
pretty hairy. Others didn't. I don't remember what 4BSD did on the
Vax, but I suspect that the page tables and enough info to find everything
on swap stayed in kernel memory. (Where's Chris Torek when you need
him? :-)
But yes, swapping was generally used to free up large amounts of memory
if under heavy load.
HTH,
Arnold