Re: [LSF/MM/BPF TOPIC] Virtual Machine Memory Passthrough

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Wed, Feb 22, 2023 at 3:27 PM Gupta, Pankaj <pankaj.gupta@amd.com> wrote:
>
> On 2/22/2023 7:18 PM, Pasha Tatashin wrote:
>
> Hi Pasha,
>
> >> Coming from the virtio-pmem and some free page hinting background, I am
> >> interested in this discussion. I saw your proposal about single owner
> >> memory driver in other thread and could not entirely link the dots about
> >> applicability of the idea with "reducing the memory footprint overhead
> >> for virtual machines". Do we plan to co-ordinate guest memory state with
> >> corresponding host state for efficient memory reclaim decisions?
> >> Or something entirely different we are targeting here?
> >
> > Hi Pankaj,
> >
> > The plan is to have a driver /dev/memctl and corresponding VMM agent
> > that synchronously passes information about how guest would like its
> > memory to be backed on the host.
> >
> > For example the following information can come from guest for a range
> > of physical addresses:
> > MADV_NOHUGEPAGE
> > MADV_HUGEPAGE
> > MADV_DONTNEED
> > PR_SET_VMA_ANON_NAME
> > etc.
> >
> > All together this should help by doing memory management operations
> > only on the host side, and reduce the number of operations that are
> > performed on the guest.
>
> o.k. That sounds like guest will have a *special* interface (paravirt?)
> for some of the memory management operations with the coordination of host.

That is correct, hence memory passthrough.

>
> Guest would still allow other regular memory operations? which would get
> full-filled by the guest? Just wondering if this solution only be
> useful for specific workloads which are aware of known MADV calls?

Depending on the flexibility of the interface, we are currently
working supporting tcmalloc(), and also mmap(MAP_ANONYMOUS), but in
the future can be extended to more types of memory.

> And might not do/require continuous allocation/deallocation of memory?

Contiguous memory allocation on the host is not required.

Thanks,
Pasha