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

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

Hi T.J,

> This topic proposal would be to present and discuss multiple MM
> features to improve host memory overcommit while running VMs. There
> are two general cases:
> 
> 1. The host and its guests operate independently,
> 
> 2. The host and its guests cooperate by techniques like ballooning.
> 
> In the first case, we would discuss some new techniques, e.g., fast
> access bit harvesting in the KVM MMU, and some difficulties, e.g.,
> double zswapping.
> 
> In the second case, we would like to discuss a novel working set size
> (WSS) notifier framework and some improvements to the ballooning
> policy. The WSS notifier, when available, can report WSS to its
> listeners. VM Memory Overcommit is one of its use cases: the
> virtio-balloon driver can register for WSS notifications and relay WSS
> to the host. The host can leverage the WSS notifications and improve
> the ballooning policy.

I am interested in this discussion. Have few questions below:

- What kind/frequency of data we expect WSS would relay to the host in
   good and worst case?

- Thoughts already considered about the overhead VM will have based on
   WSS relay data to the host and host taking action on the data?

   -- One thing iirc from the free page hinting design experiments is
      preventing guest and host acting simultaneously (e.g for free) on
      same page (pfn) and also reducing the overhead of sending data from
      guest to host by sending the highest possible page order.

Maybe some of these or other similar techniques are already considered.

Thanks,
Pankaj
> 
> This topic would be of interest to a wide range of audience, e.g.,
> phones, laptops and servers.
> Co-presented with Yuanchu Xie.
> 
> Thanks,
> 
> -T.J.
>