Re: [LSF/MM/BPF TOPIC] VM Memory Overcommit

["T.J. Alumbaugh" <talumbau@google.com>]

On Tue, Feb 28, 2023 at 2:21 AM David Hildenbrand <david@redhat.com> wrote:
>
> What we actually might want is a way to tell the OS ruining inside the
> VM to "please try not using more than XXX MiB of physical memory" but
> treat it as a soft limit. So in case we mess up, or there is a sudden
> peak in memory consumption due to a workload, we won't harm the guest
> OS/workload, and don't have to act immediately to avoid trouble. One can
> think of it like an evolution of memory ballooning: instead of creating
> artificial memory pressure by inflating the balloon that is fairly event
> driven and requires explicit memory deflation, we teach the OS to do it
> natively and pair it with free page reporting.

That's interesting. In our forthcoming balloon spec for this feature,
we provide a way to send such data from the host to the guest. We call
the general mechanism "notifications" right now, but we did not think
of that use case so far.

>
> All free physical memory inside the VM can be reported using free page
> reporting to the hypervisor, and the OS will try sticking to the
> requested "logical" VM size, unless there is real demand for more memory.
>

Yes, the two mechanisms can definitely work in tandem for such a use
case, although we have not tried that yet. Thanks for these ideas.

-T.J.