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Subject: Re: [PATCH 2/2] virtio_balloon: export 'available' memory to balloon
 statistics
To: "Michael S. Tsirkin" <mst@redhat.com>
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CC: <virtualization@lists.linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, Igor Redko <redkoi@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>
From: "Denis V. Lunev" <den@openvz.org>
Message-ID: <56CC7A37.2030807@openvz.org>
Date: Tue, 23 Feb 2016 18:26:47 +0300
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On 02/23/2016 06:10 PM, Michael S. Tsirkin wrote:
> On Tue, Feb 16, 2016 at 06:50:52PM +0300, Denis V. Lunev wrote:
>> From: Igor Redko <redkoi@virtuozzo.com>
>>
>> Add a new field, VIRTIO_BALLOON_S_AVAIL, to virtio_balloon memory
>> statistics protocol, corresponding to 'Available' in /proc/meminfo.
>>
>> It indicates to the hypervisor how big the balloon can be inflated
>> without pushing the guest system to swap.
>>
>> Signed-off-by: Igor Redko <redkoi@virtuozzo.com>
>> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Michael S. Tsirkin <mst@redhat.com>
>> CC: Andrew Morton <akpm@linux-foundation.org>
> Oops - I missed the fact that this affects host/guest ABI.
>
> Can you please submit ABI update proposal to virtio tc?
> Spec patch would be even better.
>
> This is important to ensure there are no conflicts
> with other features being developed in parallel.

hmmm

 From my point of view ABI remains untouched.
The guest can send any amount of <tag>;<value>
pairs and unknown tags are properly ignored
by the host.

That is why I think that this change is safe.