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Date: Wed, 15 Jul 2015 19:32:31 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v4 0/7] Fix QEMU crash during memory
 hotplug with vhost=on
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To: Igor Mammedov <imammedo@redhat.com>
Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, peter.maydell@linaro.org

On Wed, Jul 15, 2015 at 05:12:01PM +0200, Igor Mammedov wrote:
> On Thu,  9 Jul 2015 13:47:17 +0200
> Igor Mammedov <imammedo@redhat.com> wrote:
> 
> there also is yet another issue with vhost-user. It also has
> very low limit on amount of memory regions (if I recall correctly 8)
> and it's possible to trigger even without memory hotplug.
> one just need to start QEMU with a several -numa memdev= options
> to create a necessary amount of memory regions to trigger it.
> 
> lowrisk option to fix it would be increasing limit in vhost-user
> backend.
> 
> another option is disabling vhost and fall-back to virtio,
> but I don't know much about vhost if it's possible to 
> to switch it off without loosing packets guest was sending
> at the moment and if it will work at all with vhost.

With vhost-user you can't fall back to virtio: it's
not an accelerator, it's the backend.

Updating the protocol to support a bigger table
is possible but old remotes won't be able to support it.

-- 
MST