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

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Date:   Tue, 11 Feb 2020 16:13:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, willy@...radead.org,
        mhocko@...nel.org, linux-mm@...ck.org, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, vbabka@...e.cz,
        yang.zhang.wz@...il.com, nitesh@...hat.com, konrad.wilk@...cle.com,
        pagupta@...hat.com, riel@...riel.com, lcapitulino@...hat.com,
        dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com,
        pbonzini@...hat.com, dan.j.williams@...el.com,
        alexander.h.duyck@...ux.intel.com, osalvador@...e.de
Subject: Re: [PATCH v16.1 6/9] virtio-balloon: Add support for providing free
 page reports to host

 >> 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).

-- 
Thanks,

David / dhildenb