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

David Hildenbrand david at redhat.com
Wed Oct 14 08:26:56 UTC 2020

On 14.10.20 08:30, Michal Privoznik wrote:
> On 10/14/20 8:07 AM, Nico Pache wrote:
>> IMO "return-pages" sounds the best out of those and stays relatively 
>> consistent with the kernel and qemu terminology for this feature.
>> I personally don't see a huge problem with the current name, but I've 
>> also been staring at the words "free page reporting" for too long.
> Right, I can see both reasons. But now that Peter raised it (again, 
> sorry) at libvirt level reporting usually means "to report something to 
> user". QEMU <-> KVM communication is too low level and since this is not 
> being reported to user directly (even though it affects 
> "stat-free-memory" attribute of the balloon) reporting does sound a bit 
> weird. Let's wait for Peter's opinion.

We originally wanted to use "free page hinting", but as that name is
already taken for another virtio-balloon feature to improve live
migration speed (one time hint of free pages just before migration), we
used "reporting" instead.

On a QEMU level, this feature name makes perfect sense. The guest
(continuously) reports free pages to the hypervisor. The hypervisor
tries to use the reports to free up some memory (which might not always
be possible).

Now, all I can say is that

1. "free page reporting" is the official name of the feature. Using a
different name in libvirt will crate more confusion than it might
actually help. Just saying.

2. The proposed alternatives ""free-pages" or "return-pages" or even
"discard-pages" don't match what's actually going on.


David / dhildenb

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