Re: pool guard

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 08/09/2019 à 08:54, Jason Thorpe a écrit :
> > On Sep 8, 2019, at 9:29 AM, Maxime Villard <max%m00nbsd.net@localhost> wrote:
> > Don't confuse VA and PA. NetBSD-amd64 supports 16TB of PA, so even if
> > you have 48TB nvdimms it gets truncated to 16TB. Then, we have 32TB
> > of VA, twice more than the maximum PA. So again, we are fine.
>
> Yes, but obviously we should fix that at some point.

"Fixing" this entails first having a UVM that can scale up to and work
reasonably well with such gigantic amounts of RAM, which is far from being the
case currently. We will need to have SMP, NUMA, large pages, and in short, we
will likely have to rewrite UVM entirely.

By the time we have done all of that, the 64bit CPUs will already ship with
5-level page trees which multiply by 512 the size of the VA space, so again,
we will be largely fine.

Even otherwise, revisiting pool guards to increase the mapped/unmapped ratio
is a very insignificant and easy task.

I see no problem related to VA/PA amounts.