Re: [PATCH v3 6/8] virtio-mem: Fail if a memory backend with "prealloc=on" is specified

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* David Hildenbrand (david@redhat.com) wrote:
> "prealloc=on" for the memory backend does not work as expected, as
> virtio-mem will simply discard all preallocated memory immediately again.
> In the best case, it's an expensive NOP. In the worst case, it's an
> unexpected allocation error.
> 
> Instead, "prealloc=on" should be specified for the virtio-mem device only,
> such that virtio-mem will try preallocating memory before plugging
> memory dynamically to the guest. Fail if such a memory backend is
> provided.
> 
> Tested-by: Michal Privoznik <mprivozn@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  hw/virtio/virtio-mem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index 1ed1f5a4af..02f7b5469a 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -772,6 +772,12 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
>          error_setg(errp, "'%s' property specifies an unsupported memdev",
>                     VIRTIO_MEM_MEMDEV_PROP);
>          return;
> +    } else if (vmem->memdev->prealloc) {
> +        error_setg(errp, "'%s' property specifies a memdev with preallocation"
> +                   " enabled: %s. Instead, specify 'prealloc=on' for the"
> +                   " virtio-mem device. ", VIRTIO_MEM_MEMDEV_PROP,
> +                   object_get_canonical_path_component(OBJECT(vmem->memdev)));
> +        return;
>      }
>  
>      if ((nb_numa_nodes && vmem->node >= nb_numa_nodes) ||
> -- 
> 2.39.0
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK