implement a virtio balloon device driver

[wjhun]

We have the means to reclaim freed/unused physical pages, so make them accessible to the virtio balloon device so that they become available for other VMs.

[eyberg]

saw this on the minios mailing list just now https://lists.xenproject.org/archives/html/minios-devel/2019-12/msg00215.html

[eyberg]

#1079

[jeromegn]

Sorry to comment on an old issue, but it seemed appropriate: is the virtio-balloon device supported w/ firecracker? If so, how does one use it?

I've configured my firecracker to use a balloon device, however if I try to PATCH it (change the size of the balloon), I get an error:

{"fault_message":"Balloon config error: Error creating the balloon device: Device not activated yet."}

Config:

{
  "boot-source": {
    "kernel_image_path": "/home/jerome/.ops/0.1.52/kernel.img",
    "boot_args": "console=ttyS0 reboot=k panic=1 pci=off random.trust_cpu=on"
  },
  "drives": [
    {
      "drive_id": "rootfs",
      "path_on_host": "/home/jerome/.ops/images/app",
      "is_root_device": true,
      "is_read_only": false
    }
  ],
  "network-interfaces": [
    {
      "iface_id": "eth0",
      "guest_mac": "AA:FC:00:00:00:01",
      "host_dev_name": "tap0"
    }
  ],
  "machine-config": {
    "vcpu_count": 1,
    "mem_size_mib": 512
  },
  "balloon": {
    "amount_mib": 0,
    "deflate_on_oom": false,
    "stats_polling_interval_s": 1
  },
  "logger": {
    "log_path": "logs.fifo",
    "level": "Debug"
  },
  "metrics": {
    "metrics_path": "metrics.fifo"
  },
  "vsock": {
    "guest_cid": 3,
    "uds_path": "./v.sock"
  }
}

[francescolavra]

Nanos currently supports virtio-balloon devices only when wired to the PCI bus; Firecracker doesn't have PCI, so its virtio-balloon devices are not PCI devices (they are most likely accessed via MMIO) and therefore not currently supported.

[francescolavra]

#2081 adds support for the virtio-balloon device in Firecracker.
To download a kernel build with this feature, you can use a dummy ops image create (or ops run) command with the --nanos-version 05536fb command line option: this will place the kernel binary file at ~/.ops/05536fb/kernel.img; then, you can use this path as "kernel_image_path" in your Firecracker configuration file.