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

["Gupta, Pankaj" <pankaj.gupta@amd.com>]

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.

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

Thanks,
Pankaj
> 
> The /dev/som can help with allowing support for anonymous memory in
> the guest with 1G pages that are only partially backed on the host
> side, thus yielding to faster guestVA hostPA translations.
> 
> Pasha