bhyve uses all available memory during IO-intensive operations

[K. Macy]

On Fri, Dec 1, 2017 at 20:02 Rodney W. Grimes <
freebsd-rwg at pdx.rh.cn85.dnsmgr.net> wrote:

> > On 02/12/2017 08:11, Dustin Wenz wrote:
> > >
> > > The commit history shows that chyves defaults to -S if you are
> > > hosting from FreeBSD 10.3 or later. I'm sure they had a reason for
> > > doing that, but I don't know what that would be. It seems to an
> > > inefficient use of main memory if you need to run a lot of VMs.
> >
> > It sounds like a reasonable solution to a problem. If host memory is
> > full it swaps some out, so a bhyve might have free mem but some could be
> > swapped out by the host. If the bhyve is out of mem, it's system swaps
> > to it's disk, so the host swaps it back in so that the bhyve can then
> > swap it to its disk...
> >
> > Wiring bhyve ram might be a reasonable solution as long as the hosts
> > physical ram isn't over allocated by bhyve guests.
> >
> > The best solution would involve a host and guest talking to each other
> > about used mem, but that would break the whole virtual machine illusion.
> > At the least it would involve a system telling the hardware what memory
> > is used and what is not, which just isn't something any system does.
> > Maybe that is an idea for the vm guest aware systems of the future.
>
> Its actually old technology, its called the memory balloon driver,
> but bhyve does not have that functionality, yet.
>
>

The virtio ballon driver is already there. Implementing a kernel backend
for it would be trivial. In kernel virtio-net and virtio-p9fs backends are
already well underway.

-M


> --
> Rod Grimes
> rgrimes at freebsd.org
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