ZFS Snapshotter - Excessive ZFS Snapshots?

Description

Seem to be having an issue with containerd ZFS snapshotter potentially not cleaning up snapshots?

Looking at systemd logs, I noticed message such as (not sure if related):

k3s01 k3s[1094942]: E0901 10:54:34.173751 1094942 cri_stats_provider.go:455] "Failed to get the info of the filesystem with mountpoint" err="unable to find data in memory cache" mountpoint="/var/lib/containerd/io.containerd.snapshotter.v1.zfs"

k3s01 k3s[1094942]: E0901 10:54:34.173789 1094942 kubelet.go:1298] "Image garbage collection failed once. Stats initialization may not have completed yet" err="invalid capacity 0 on image filesystem"

Containerd zfs dataset ranges between 34% to 80% capacity depending on when various cleanup and garbage collection happens. It has never reached zero.

This number of snapshots seems high:

$ zfs list -r -t snapshot rpool/containerd | wc -l
1347

For less than 70 containers:

$ sudo crictl ps | wc -l
68

Steps to reproduce the issue

1. 2. 3.

Describe the results you received and expected

Expecting more snapshots to be deleted overtime, but unsure how to verify existing snapshots are actually valid or not.

What version of containerd are you using?

containerd github.com/containerd/containerd 1.5.9-0ubuntu3

Any other relevant information

$ runc --version
runc version 1.1.0-0ubuntu1
spec: 1.0.2-dev
go: go1.17.3
libseccomp: 2.5.3

$ sudo crictl info
{
  "status": {
    "conditions": [
      {
        "type": "RuntimeReady",
        "status": true,
        "reason": "",
        "message": ""
      },
      {
        "type": "NetworkReady",
        "status": true,
        "reason": "",
        "message": ""
      }
    ]
  },
  "cniconfig": {
    "PluginDirs": [
      "/usr/lib/cni"
    ],
    "PluginConfDir": "/etc/cni/net.d",
    "PluginMaxConfNum": 1,
    "Prefix": "eth",
    "Networks": [
      {
        "Config": {
          "Name": "cni-loopback",
          "CNIVersion": "0.3.1",
          "Plugins": [
            {
              "Network": {
                "type": "loopback",
                "ipam": {},
                "dns": {}
              },
              "Source": "{\"type\":\"loopback\"}"
            }
          ],
          "Source": "{\n\"cniVersion\": \"0.3.1\",\n\"name\": \"cni-loopback\",\n\"plugins\": [{\n  \"type\": \"loopback\"\n}]\n}"
        },
        "IFName": "lo"
      },
      {
        "Config": {
          "Name": "cbr0",
          "CNIVersion": "0.3.1",
          "Plugins": [
            {
              "Network": {
                "type": "flannel",
                "ipam": {},
                "dns": {}
              },
              "Source": "{\"delegate\":{\"forceAddress\":true,\"hairpinMode\":true,\"isDefaultGateway\":true},\"type\":\"flannel\"}"
            },
            {
              "Network": {
                "type": "portmap",
                "capabilities": {
                  "portMappings": true
                },
                "ipam": {},
                "dns": {}
              },
              "Source": "{\"capabilities\":{\"portMappings\":true},\"type\":\"portmap\"}"
            }
          ],
          "Source": "{\n  \"name\":\"cbr0\",\n  \"cniVersion\":\"0.3.1\",\n  \"plugins\":[\n    {\n      \"type\":\"flannel\",\n      \"delegate\":{\n        \"hairpinMode\":true,\n        \"forceAddress\":true,\n        \"isDefaultGateway\":true\n      }\n    },\n    {\n      \"type\":\"portmap\",\n      \"capabilities\":{\n        \"portMappings\":true\n      }\n    }\n  ]\n}"
        },
        "IFName": "eth0"
      }
    ]
  },
  "config": {
    "containerd": {
      "snapshotter": "zfs",
      "defaultRuntimeName": "runc",
      "defaultRuntime": {
        "runtimeType": "",
        "runtimeEngine": "",
        "PodAnnotations": [],
        "ContainerAnnotations": [],
        "runtimeRoot": "",
        "options": {},
        "privileged_without_host_devices": false,
        "baseRuntimeSpec": ""
      },
      "untrustedWorkloadRuntime": {
        "runtimeType": "",
        "runtimeEngine": "",
        "PodAnnotations": [],
        "ContainerAnnotations": [],
        "runtimeRoot": "",
        "options": {},
        "privileged_without_host_devices": false,
        "baseRuntimeSpec": ""
      },
      "runtimes": {
        "runc": {
          "runtimeType": "io.containerd.runc.v2",
          "runtimeEngine": "",
          "PodAnnotations": [],
          "ContainerAnnotations": [],
          "runtimeRoot": "",
          "options": {
            "BinaryName": "",
            "CriuImagePath": "",
            "CriuPath": "",
            "CriuWorkPath": "",
            "IoGid": 0,
            "IoUid": 0,
            "NoNewKeyring": false,
            "NoPivotRoot": false,
            "Root": "",
            "ShimCgroup": "",
            "SystemdCgroup": false
          },
          "privileged_without_host_devices": false,
          "baseRuntimeSpec": ""
        }
      },
      "noPivot": false,
      "disableSnapshotAnnotations": true,
      "discardUnpackedLayers": false
    },
    "cni": {
      "binDir": "/usr/lib/cni",
      "confDir": "/etc/cni/net.d",
      "maxConfNum": 1,
      "confTemplate": ""
    },
    "registry": {
      "configPath": "",
      "mirrors": {},
      "configs": {},
      "auths": {},
      "headers": {
        "User-Agent": [
          "containerd/1.5.9-0ubuntu3"
        ]
      }
    },
    "imageDecryption": {
      "keyModel": "node"
    },
    "disableTCPService": true,
    "streamServerAddress": "127.0.0.1",
    "streamServerPort": "0",
    "streamIdleTimeout": "4h0m0s",
    "enableSelinux": false,
    "selinuxCategoryRange": 1024,
    "sandboxImage": "k8s.gcr.io/pause:3.5",
    "statsCollectPeriod": 10,
    "systemdCgroup": false,
    "enableTLSStreaming": false,
    "x509KeyPairStreaming": {
      "tlsCertFile": "",
      "tlsKeyFile": ""
    },
    "maxContainerLogSize": 16384,
    "disableCgroup": false,
    "disableApparmor": false,
    "restrictOOMScoreAdj": false,
    "maxConcurrentDownloads": 3,
    "disableProcMount": false,
    "unsetSeccompProfile": "",
    "tolerateMissingHugetlbController": true,
    "disableHugetlbController": true,
    "ignoreImageDefinedVolumes": false,
    "netnsMountsUnderStateDir": false,
    "containerdRootDir": "/var/lib/containerd",
    "containerdEndpoint": "/run/containerd/containerd.sock",
    "rootDir": "/var/lib/containerd/io.containerd.grpc.v1.cri",
    "stateDir": "/run/containerd/io.containerd.grpc.v1.cri"
  },
  "golang": "go1.18",
  "lastCNILoadStatus": "OK"
}

$ uname -a
Linux k3s01 5.15.0-47-generic containerd/containerd#51-Ubuntu SMP Thu Aug 11 07:51:15 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Show configuration if it is related to CRI plugin.

$ cat /etc/containerd/config.toml 
disabled_plugins = []
imports = []
oom_score = 0
plugin_dir = ""
required_plugins = []
root = "/var/lib/containerd"
state = "/run/containerd"
version = 2

[cgroup]
  path = ""

[debug]
  address = ""
  format = ""
  gid = 0
  level = ""
  uid = 0

[grpc]
  address = "/run/containerd/containerd.sock"
  gid = 0
  max_recv_message_size = 16777216
  max_send_message_size = 16777216
  tcp_address = ""
  tcp_tls_cert = ""
  tcp_tls_key = ""
  uid = 0

[metrics]
  address = ""
  grpc_histogram = false

[plugins]

  [plugins."io.containerd.gc.v1.scheduler"]
    deletion_threshold = 0
    mutation_threshold = 100
    pause_threshold = 0.02
    schedule_delay = "0s"
    startup_delay = "100ms"

  [plugins."io.containerd.grpc.v1.cri"]
    disable_apparmor = false
    disable_cgroup = false
    disable_hugetlb_controller = true
    disable_proc_mount = false
    disable_tcp_service = true
    enable_selinux = false
    enable_tls_streaming = false
    ignore_image_defined_volumes = false
    max_concurrent_downloads = 3
    max_container_log_line_size = 16384
    netns_mounts_under_state_dir = false
    restrict_oom_score_adj = false
    sandbox_image = "k8s.gcr.io/pause:3.5"
    selinux_category_range = 1024
    stats_collect_period = 10
    stream_idle_timeout = "4h0m0s"
    stream_server_address = "127.0.0.1"
    stream_server_port = "0"
    systemd_cgroup = false
    tolerate_missing_hugetlb_controller = true
    unset_seccomp_profile = ""

    [plugins."io.containerd.grpc.v1.cri".cni]
      bin_dir = "/usr/lib/cni"
      conf_dir = "/etc/cni/net.d"
      conf_template = ""
      max_conf_num = 1

    [plugins."io.containerd.grpc.v1.cri".containerd]
      default_runtime_name = "runc"
      disable_snapshot_annotations = true
      discard_unpacked_layers = false
      no_pivot = false
      snapshotter = "zfs"

      [plugins."io.containerd.grpc.v1.cri".containerd.default_runtime]
        base_runtime_spec = ""
        container_annotations = []
        pod_annotations = []
        privileged_without_host_devices = false
        runtime_engine = ""
        runtime_root = ""
        runtime_type = ""

        [plugins."io.containerd.grpc.v1.cri".containerd.default_runtime.options]

      [plugins."io.containerd.grpc.v1.cri".containerd.runtimes]

        [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
          base_runtime_spec = ""
          container_annotations = []
          pod_annotations = []
          privileged_without_host_devices = false
          runtime_engine = ""
          runtime_root = ""
          runtime_type = "io.containerd.runc.v2"

          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
            BinaryName = ""
            CriuImagePath = ""
            CriuPath = ""
            CriuWorkPath = ""
            IoGid = 0
            IoUid = 0
            NoNewKeyring = false
            NoPivotRoot = false
            Root = ""
            ShimCgroup = ""
            SystemdCgroup = false

      [plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime]
        base_runtime_spec = ""
        container_annotations = []
        pod_annotations = []
        privileged_without_host_devices = false
        runtime_engine = ""
        runtime_root = ""
        runtime_type = ""

        [plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime.options]

    [plugins."io.containerd.grpc.v1.cri".image_decryption]
      key_model = "node"

    [plugins."io.containerd.grpc.v1.cri".registry]
      config_path = ""

      [plugins."io.containerd.grpc.v1.cri".registry.auths]

      [plugins."io.containerd.grpc.v1.cri".registry.configs]

      [plugins."io.containerd.grpc.v1.cri".registry.headers]

      [plugins."io.containerd.grpc.v1.cri".registry.mirrors]

    [plugins."io.containerd.grpc.v1.cri".x509_key_pair_streaming]
      tls_cert_file = ""
      tls_key_file = ""

  [plugins."io.containerd.internal.v1.opt"]
    path = "/opt/containerd"

  [plugins."io.containerd.internal.v1.restart"]
    interval = "10s"

  [plugins."io.containerd.metadata.v1.bolt"]
    content_sharing_policy = "shared"

  [plugins."io.containerd.monitor.v1.cgroups"]
    no_prometheus = false

  [plugins."io.containerd.runtime.v1.linux"]
    no_shim = false
    runtime = "runc"
    runtime_root = ""
    shim = "containerd-shim"
    shim_debug = false

  [plugins."io.containerd.runtime.v2.task"]
    platforms = ["linux/amd64"]

  [plugins."io.containerd.service.v1.diff-service"]
    default = ["walking"]

  [plugins."io.containerd.snapshotter.v1.aufs"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.btrfs"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.devmapper"]
    async_remove = false
    base_image_size = ""
    pool_name = ""
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.native"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.overlayfs"]
    root_path = ""

  [plugins."io.containerd.snapshotter.v1.zfs"]
    root_path = ""

[proxy_plugins]

[stream_processors]

  [stream_processors."io.containerd.ocicrypt.decoder.v1.tar"]
    accepts = ["application/vnd.oci.image.layer.v1.tar+encrypted"]
    args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
    env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
    path = "ctd-decoder"
    returns = "application/vnd.oci.image.layer.v1.tar"

  [stream_processors."io.containerd.ocicrypt.decoder.v1.tar.gzip"]
    accepts = ["application/vnd.oci.image.layer.v1.tar+gzip+encrypted"]
    args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
    env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
    path = "ctd-decoder"
    returns = "application/vnd.oci.image.layer.v1.tar+gzip"

[timeouts]
  "io.containerd.timeout.shim.cleanup" = "5s"
  "io.containerd.timeout.shim.load" = "5s"
  "io.containerd.timeout.shim.shutdown" = "3s"
  "io.containerd.timeout.task.state" = "2s"

[ttrpc]
  address = ""
  gid = 0
  uid = 0

containerd / zfs