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

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

>> 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.

ya.

> 
>>
>> 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.

Not sure if its worth to extend the existing paravirt memory management 
interfaces like virtio-mem or virtio-balloon or create a new driver 
altogether? Adding David (in Cc) for his thoughts.

Thanks,
Pankaj

> 
>> And might not do/require continuous allocation/deallocation of memory?
> 
> Contiguous memory allocation on the host is not required.
> 
> Thanks,
> Pasha