Re: [PATCH v16.1 6/9] virtio-balloon: Add support for providing free page reports to host

[Alexander Duyck]

On Tue, 2020-02-11 at 16:13 +0100, David Hildenbrand wrote:
>  >> AFAIKs, the guest could inflate/deflate (esp. temporarily) and
> > > communicate via "actual" the actual balloon size as he sees it.
> > 
> > OK so you want hinted but unused pages counted, and reported
> > in "actual"? That's a vmexit before each page use ...
> 
> No, not at all. I rather meant, that it is unclear how
> inflation/deflation requests and "actual" *could* interact. Especially
> if we would consider free page reporting as some way of inflation
> (+immediate deflation) triggered by the guest. IMHO, we would not touch
> "actual" in that case.
> 
> But as I said, I am totally fine with keeping it as is in this patch.
> IOW not glue free page reporting to inflation/deflation but let it act
> like something different with its own semantics (and document these
> properly).
> 

Okay, so before I post v17 am I leaving the virtio-balloon changes as they
were then?

For what it is worth I agree with Michael that there is more to this than
just a scatter-gather queue. For now I am trying to keep the overall
impact on QEMU on the smaller side, and if we do end up supporting the
MADV_FREE instead of MADV_DONTNEED that would also have an impact on
things as it would be yet another difference between ballooning and
hinting.

Thanks.

- Alex