[PATCH v2 0/4] qemu: Add support for free-page-reporting

David Hildenbrand david at redhat.com
Tue Oct 13 17:04:47 UTC 2020

On 13.10.20 19:00, Nico Pache wrote:
> I don't believe so, but David might have some more insight into that
> question. 
> Once the feature is enabled the guest will report pages on its freelist
> to the hypervisor, and the host/hypervisor will then release them. 

We report (some, not all) free memory of our guest to the hypervisor. So
whatever the guest reported shows up in "stat-free-memory" in the stats

The hypervisor will "discard" backing storage of reported free memory,
resulting in your hypervisor having more free memory available (and the
QEMU process consuming less memory).

> I'm not exactly sure what information we can or would want to 'stat' out
> of this process... A counter for number of pages returned?

As the guest can reuse memory any time without coordination with the
hypervisor that wouldn't be of too much help. A counter would only tell
you if free page reporting was once performed successfully.

You would really have to compare the QEMU process memory footprint with
the guest stats to figure out if free page reporting is doing what it's
supposed to do.


David / dhildenb

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