[TUHS] /dev/drum

arnold at skeeve.com arnold at skeeve.com
Thu Apr 26 00:02:24 AEST 2018

> On 25 Apr 2018, at 13:18, Ronald Natalie <ron at ronnatalie.com> wrote:
> > 
> > Early pages were 1K.

Tim Bradshaw <tfb at 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.



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