SUnreclaim increases after launch-delete containers

Hi,
We are running LXD containers to simulate several kinds of network clients. We launch the containers, run some tests and delete the containers. After couple runs of testing, the host has little available memory left.
I’ve tried to reproduce this issue, following are the reproduce steps:

  1. Launch a VM using image ubuntu-minial:22.04

  2. Login the Ubuntu VM

    root@ubuntu:~# uname -a
    Linux ubuntu 5.15.0-1051-kvm #56-Ubuntu SMP Thu Feb 8 23:30:16 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
    
  3. Record SUnreclaim

    root@ubuntu:~# cat /proc/meminfo |grep SUn
    SUnreclaim:        92604 kB
    
  4. Launch a container using ubuntu-minimal:23.04

    lxc launch ubuntu-minimal:23.04 test-container
    
  5. Delete the container

    lxc delete test-container --force
    
  6. Check SUnreclaim

    root@ubuntu:~# cat /proc/meminfo |grep SUn
    SUnreclaim:        93228 kB
    
  7. After each round of launch-delete, the SUnreclaim increases by ~500KB.

LXC information:

root@ubuntu:~# lxc info
config: {}
api_extensions:
- storage_zfs_remove_snapshots
- container_host_shutdown_timeout
- container_stop_priority
- container_syscall_filtering
- auth_pki
- container_last_used_at
- etag
- patch
- usb_devices
- https_allowed_credentials
- image_compression_algorithm
- directory_manipulation
- container_cpu_time
- storage_zfs_use_refquota
- storage_lvm_mount_options
- network
- profile_usedby
- container_push
- container_exec_recording
- certificate_update
- container_exec_signal_handling
- gpu_devices
- container_image_properties
- migration_progress
- id_map
- network_firewall_filtering
- network_routes
- storage
- file_delete
- file_append
- network_dhcp_expiry
- storage_lvm_vg_rename
- storage_lvm_thinpool_rename
- network_vlan
- image_create_aliases
- container_stateless_copy
- container_only_migration
- storage_zfs_clone_copy
- unix_device_rename
- storage_lvm_use_thinpool
- storage_rsync_bwlimit
- network_vxlan_interface
- storage_btrfs_mount_options
- entity_description
- image_force_refresh
- storage_lvm_lv_resizing
- id_map_base
- file_symlinks
- container_push_target
- network_vlan_physical
- storage_images_delete
- container_edit_metadata
- container_snapshot_stateful_migration
- storage_driver_ceph
- storage_ceph_user_name
- resource_limits
- storage_volatile_initial_source
- storage_ceph_force_osd_reuse
- storage_block_filesystem_btrfs
- resources
- kernel_limits
- storage_api_volume_rename
- macaroon_authentication
- network_sriov
- console
- restrict_devlxd
- migration_pre_copy
- infiniband
- maas_network
- devlxd_events
- proxy
- network_dhcp_gateway
- file_get_symlink
- network_leases
- unix_device_hotplug
- storage_api_local_volume_handling
- operation_description
- clustering
- event_lifecycle
- storage_api_remote_volume_handling
- nvidia_runtime
- container_mount_propagation
- container_backup
- devlxd_images
- container_local_cross_pool_handling
- proxy_unix
- proxy_udp
- clustering_join
- proxy_tcp_udp_multi_port_handling
- network_state
- proxy_unix_dac_properties
- container_protection_delete
- unix_priv_drop
- pprof_http
- proxy_haproxy_protocol
- network_hwaddr
- proxy_nat
- network_nat_order
- container_full
- candid_authentication
- backup_compression
- candid_config
- nvidia_runtime_config
- storage_api_volume_snapshots
- storage_unmapped
- projects
- candid_config_key
- network_vxlan_ttl
- container_incremental_copy
- usb_optional_vendorid
- snapshot_scheduling
- snapshot_schedule_aliases
- container_copy_project
- clustering_server_address
- clustering_image_replication
- container_protection_shift
- snapshot_expiry
- container_backup_override_pool
- snapshot_expiry_creation
- network_leases_location
- resources_cpu_socket
- resources_gpu
- resources_numa
- kernel_features
- id_map_current
- event_location
- storage_api_remote_volume_snapshots
- network_nat_address
- container_nic_routes
- rbac
- cluster_internal_copy
- seccomp_notify
- lxc_features
- container_nic_ipvlan
- network_vlan_sriov
- storage_cephfs
- container_nic_ipfilter
- resources_v2
- container_exec_user_group_cwd
- container_syscall_intercept
- container_disk_shift
- storage_shifted
- resources_infiniband
- daemon_storage
- instances
- image_types
- resources_disk_sata
- clustering_roles
- images_expiry
- resources_network_firmware
- backup_compression_algorithm
- ceph_data_pool_name
- container_syscall_intercept_mount
- compression_squashfs
- container_raw_mount
- container_nic_routed
- container_syscall_intercept_mount_fuse
- container_disk_ceph
- virtual-machines
- image_profiles
- clustering_architecture
- resources_disk_id
- storage_lvm_stripes
- vm_boot_priority
- unix_hotplug_devices
- api_filtering
- instance_nic_network
- clustering_sizing
- firewall_driver
- projects_limits
- container_syscall_intercept_hugetlbfs
- limits_hugepages
- container_nic_routed_gateway
- projects_restrictions
- custom_volume_snapshot_expiry
- volume_snapshot_scheduling
- trust_ca_certificates
- snapshot_disk_usage
- clustering_edit_roles
- container_nic_routed_host_address
- container_nic_ipvlan_gateway
- resources_usb_pci
- resources_cpu_threads_numa
- resources_cpu_core_die
- api_os
- container_nic_routed_host_table
- container_nic_ipvlan_host_table
- container_nic_ipvlan_mode
- resources_system
- images_push_relay
- network_dns_search
- container_nic_routed_limits
- instance_nic_bridged_vlan
- network_state_bond_bridge
- usedby_consistency
- custom_block_volumes
- clustering_failure_domains
- resources_gpu_mdev
- console_vga_type
- projects_limits_disk
- network_type_macvlan
- network_type_sriov
- container_syscall_intercept_bpf_devices
- network_type_ovn
- projects_networks
- projects_networks_restricted_uplinks
- custom_volume_backup
- backup_override_name
- storage_rsync_compression
- network_type_physical
- network_ovn_external_subnets
- network_ovn_nat
- network_ovn_external_routes_remove
- tpm_device_type
- storage_zfs_clone_copy_rebase
- gpu_mdev
- resources_pci_iommu
- resources_network_usb
- resources_disk_address
- network_physical_ovn_ingress_mode
- network_ovn_dhcp
- network_physical_routes_anycast
- projects_limits_instances
- network_state_vlan
- instance_nic_bridged_port_isolation
- instance_bulk_state_change
- network_gvrp
- instance_pool_move
- gpu_sriov
- pci_device_type
- storage_volume_state
- network_acl
- migration_stateful
- disk_state_quota
- storage_ceph_features
- projects_compression
- projects_images_remote_cache_expiry
- certificate_project
- network_ovn_acl
- projects_images_auto_update
- projects_restricted_cluster_target
- images_default_architecture
- network_ovn_acl_defaults
- gpu_mig
- project_usage
- network_bridge_acl
- warnings
- projects_restricted_backups_and_snapshots
- clustering_join_token
- clustering_description
- server_trusted_proxy
- clustering_update_cert
- storage_api_project
- server_instance_driver_operational
- server_supported_storage_drivers
- event_lifecycle_requestor_address
- resources_gpu_usb
- clustering_evacuation
- network_ovn_nat_address
- network_bgp
- network_forward
- custom_volume_refresh
- network_counters_errors_dropped
- metrics
- image_source_project
- clustering_config
- network_peer
- linux_sysctl
- network_dns
- ovn_nic_acceleration
- certificate_self_renewal
- instance_project_move
- storage_volume_project_move
- cloud_init
- network_dns_nat
- database_leader
- instance_all_projects
- clustering_groups
- ceph_rbd_du
- instance_get_full
- qemu_metrics
- gpu_mig_uuid
- event_project
- clustering_evacuation_live
- instance_allow_inconsistent_copy
- network_state_ovn
- storage_volume_api_filtering
- image_restrictions
- storage_zfs_export
- network_dns_records
- storage_zfs_reserve_space
- network_acl_log
- storage_zfs_blocksize
- metrics_cpu_seconds
- instance_snapshot_never
- certificate_token
- instance_nic_routed_neighbor_probe
- event_hub
- agent_nic_config
- projects_restricted_intercept
- metrics_authentication
- images_target_project
- cluster_migration_inconsistent_copy
- cluster_ovn_chassis
- container_syscall_intercept_sched_setscheduler
- storage_lvm_thinpool_metadata_size
- storage_volume_state_total
- instance_file_head
- instances_nic_host_name
- image_copy_profile
- container_syscall_intercept_sysinfo
- clustering_evacuation_mode
- resources_pci_vpd
- qemu_raw_conf
- storage_cephfs_fscache
- network_load_balancer
- vsock_api
- instance_ready_state
- network_bgp_holdtime
- storage_volumes_all_projects
- metrics_memory_oom_total
- storage_buckets
- storage_buckets_create_credentials
- metrics_cpu_effective_total
- projects_networks_restricted_access
- storage_buckets_local
- loki
- acme
- internal_metrics
- cluster_join_token_expiry
- remote_token_expiry
- init_preseed
- storage_volumes_created_at
- cpu_hotplug
- projects_networks_zones
- network_txqueuelen
- cluster_member_state
- instances_placement_scriptlet
- storage_pool_source_wipe
- zfs_block_mode
- instance_generation_id
- disk_io_cache
- amd_sev
- storage_pool_loop_resize
- migration_vm_live
- ovn_nic_nesting
- oidc
- network_ovn_l3only
- ovn_nic_acceleration_vdpa
- cluster_healing
- instances_state_total
- auth_user
- security_csm
- instances_rebuild
- numa_cpu_placement
- custom_volume_iso
- network_allocations
- storage_api_remote_volume_snapshot_copy
- zfs_delegate
- operations_get_query_all_projects
- metadata_configuration
- syslog_socket
- event_lifecycle_name_and_project
- instances_nic_limits_priority
- disk_initial_volume_configuration
- operation_wait
- cluster_internal_custom_volume_copy
- disk_io_bus
- storage_cephfs_create_missing
- instance_move_config
api_status: stable
api_version: "1.0"
auth: trusted
public: false
auth_methods:
- tls
auth_user_name: root
auth_user_method: unix
environment:
  addresses: []
  architectures:
  - x86_64
  - i686
  certificate: |
    -----BEGIN CERTIFICATE-----
    MIIB4zCCAWmgAwIBAgIQW032jTyQQbu12hoBEcPh5zAKBggqhkjOPQQDAzAkMQww
    CgYDVQQKEwNMWEQxFDASBgNVBAMMC3Jvb3RAdWJ1bnR1MB4XDTI0MDMwNzA3NTYz
    OFoXDTM0MDMwNTA3NTYzOFowJDEMMAoGA1UEChMDTFhEMRQwEgYDVQQDDAtyb290
    QHVidW50dTB2MBAGByqGSM49AgEGBSuBBAAiA2IABDa4h3SvOZqVb5bxftqenHlM
    NjG3OemNF+mY3uPErmd20Fr4qoor4j/7GCzvApvMDEvuD0DE2T0LkvJnUSBbmkRX
    kBa0b1pu1eeZa9ifNgKkD/nVY7p6zM/E45GefErDI6NgMF4wDgYDVR0PAQH/BAQD
    AgWgMBMGA1UdJQQMMAoGCCsGAQUFBwMBMAwGA1UdEwEB/wQCMAAwKQYDVR0RBCIw
    IIIGdWJ1bnR1hwR/AAABhxAAAAAAAAAAAAAAAAAAAAABMAoGCCqGSM49BAMDA2gA
    MGUCMQChlmwdahgeeSe4XxUbAvx+NxKZTLO/rWyjrUYuJhKERJazQAhAcmvbsTjt
    P7H7nLUCMGDRbe9QrKbglsoJIqGDi4smj0OngW7SM6IfFpPI6EegrScl1FmBgnG6
    apojldPoGg==
    -----END CERTIFICATE-----
  certificate_fingerprint: e51c0f80a1e8be5f4a41f809a74499b7c20544b29da1e3b4903fdba44c5d6d69
  driver: qemu | lxc
  driver_version: 8.1.3 | 5.0.3
  firewall: nftables
  kernel: Linux
  kernel_architecture: x86_64
  kernel_features:
    idmapped_mounts: "true"
    netnsid_getifaddrs: "true"
    seccomp_listener: "true"
    seccomp_listener_continue: "true"
    uevent_injection: "true"
    unpriv_fscaps: "true"
  kernel_version: 5.15.0-1051-kvm
  lxc_features:
    cgroup2: "true"
    core_scheduling: "true"
    devpts_fd: "true"
    idmapped_mounts_v2: "true"
    mount_injection_file: "true"
    network_gateway_device_route: "true"
    network_ipvlan: "true"
    network_l2proxy: "true"
    network_phys_macvlan_mtu: "true"
    network_veth_router: "true"
    pidfd: "true"
    seccomp_allow_deny_syntax: "true"
    seccomp_notify: "true"
    seccomp_proxy_send_notify_fd: "true"
  os_name: Ubuntu
  os_version: "22.04"
  project: default
  server: lxd
  server_clustered: false
  server_event_mode: full-mesh
  server_name: ubuntu
  server_pid: 1758
  server_version: "5.20"
  storage: zfs
  storage_version: 2.1.5-1ubuntu6~22.04.2
  storage_supported_drivers:
  - name: dir
    version: "1"
    remote: false
  - name: lvm
    version: 2.03.11(2) (2021-01-08) / 1.02.175 (2021-01-08) / 4.45.0
    remote: false
  - name: zfs
    version: 2.1.5-1ubuntu6~22.04.2
    remote: false
  - name: btrfs
    version: 5.16.2
    remote: false
  - name: ceph
    version: 17.2.6
    remote: true
  - name: cephfs
    version: 17.2.6
    remote: true
  - name: cephobject
    version: 17.2.6
    remote: true

Any suggestions for what I could try?

I cannot replicate with Incus.

Specifically,

$ cat /proc/meminfo |grep SUnreclaim
SUnreclaim:       767584 kB
$ incus launch images:debian/12 test001 --vm
Launching test001
$ cat /proc/meminfo |grep SUnreclaim
SUnreclaim:       855460 kB
$ incus delete test001 --force
$ cat /proc/meminfo |grep SUnreclaim
SUnreclaim:       767584 kB
$ 

Thanks. I will try incus.

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