User:Johannbg/Systemd/cgroup-changes

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Systemd cgroups changes

Per-controller hierarchies are going away ( in other words the cgroups tree can no longer be considered a shared resource )and is being replaced by an single kernel cgroup hierarchy which will allow controllers to be individually enabled for each cgroup with the hierarchies the controllers see always being subtrees of the full single hierarchy.

This hierarchy is a private property of systemd as in systemd will set it up, systemd will maintain it, systemd will rearrange it.

Other software that wants to make use of cgroups can only do so through systemd's APIs.

Systemd unit changes

Important.png
The lower level cgroup configuration options as in ControlGroup* as well as "DefaultControllers* are being deprecated!!!

Introduction of slice unit

There are four .slice units which form the basis of the hierarchy for assignment of resources for services, users, and virtual machines or containers.

The .slice is the root of the hierarchy. It does not contain services directly, but is used to set defaults for the whole tree.


The machine.slice contains virtual machines and containers registered with systemd-machined and is where all running VMs/containers are located by default.


/sys/fs/cgroup/

`-- systemd

    |-- machine.slice
    |...

The system.slice contains services started by systemd and is where all system services are located by default.

/sys/fs/cgroup/
`-- systemd
    |-- machine.slice
    |...
    |-- system.slice
    |...

The user.slice contains user processes and services started on behalf of the user, including the per-user systemd instance and is where all logged in users are located by default.

/sys/fs/cgroup/
`-- systemd
    |-- machine.slice
    |...
    |-- system.slice
    |...
    `-- user.slice

The higher level cgroup option which are available and can be used in the following type units slice.slice, scope.scope, service.service, socket.socket, mount.mount, swap.swap are...

CPUAccounting=
CPUShares=
MemoryAccounting=
MemoryLimit=
MemorySoftLimit=
BlockIOAccounting=
BlockIOWeight=
BlockIODeviceWeight=
BlockIOReadBandwidth=
BlockIOWriteBandwidth=
DeviceAllow=
DevicePolicy=
Slice=
Note.png
Usage of any of the following higher level cgroup options for one or more of the following unit options might also implicitly turn it on for all units contained in the same slice and for all its parent slices and the units contained therein.
CPUAccounting= 
CPUShares=
MemoryAccounting=
MemoryLimit= 
MemorySoftLimit=
BlockIOAccounting=
BlockIOWeight=
BlockIODeviceWeight=
BlockIOReadBandwidth=
BlockIOWriteBandwidth=
Idea.png
To disable this behaviour set corresponding resource accounting entry to no.

Introduction of scopes unit

Scope units are not configured via unit configuration files, but are only created programmatically using the bus interfaces of systemd. They are named similar to filenames. A unit whose name ends in ".scope" refers to a scope unit. Scopes units manage a set of system processes. Unlike service units, scope units manage externally created processes, and do not fork off processes on its own.

systemd-run --scope <command> may be used to launch a command in a new scope unit from the command line.

Default system setup

/sys/fs/cgroup/

`-- systemd

    |-- machine.slice

    |   `-- machine-f20.scope

    |       |-- system.slice

    |       |   |-- console-getty.service

    |       |   |-- systemd-journald.service

    |       |   `-- ...

    |       `-- user.slice

    |

    |-- system.slice

    |   |-- cups.service

    |   |-- ntpd.service

    |   |-- systemd-journald.service

    |   |-- systemd-udevd.service

    |   `-- …

    |

    `-- user.slice

        |-- user-1000.slice

        |   |-- systemd-user@1000.service

        |   |   |-- firefox.service

        |   |   |-- gnome-shell.service

        |   |   `-- ...

        |   `-- session-1.scope

        |

        `-- user-2702.slice

            |-- systemd-user@2702.service

            |   `-- ...

            |-- session-2.scope

            `-- session-3.scope

Slices for infrastructure/isp/customers

/sys/fs/cgroup/

`-- systemd

    |-- machine.slice

    |   |-- machine-web-customer.slice

    |   |   |-- machine-web-development.scope

    |   |   |   `-- system.slice

    |   |   |       |-- httpd.service

    |   |   |       |-- systemd-journald.service

    |   |   |       `-- ...

    |   |   |

    |   |   |-- machine-web-staging.scope

    |   |   |   `-- system.slice

    |   |   |       |-- httpd.service

    |   |   |       |-- systemd-journald.service

    |   |   |       `-- ...

    |   |   |

    |   |   `-- machine-web-production.scope

    |   |       `-- system.slice

    |   |           |-- httpd.service

    |   |           |-- systemd-journald.service

    |   |           `-- ...

    |   |

    |   `-- machine-postgresql-customer.slice

    |       |-- machine-postgresql.slice

    |           `-- machine-postgresql.scope

    |               `-- system.slice

    |                   |-- postgresql.service

    |                   |-- systemd-journald.service

    |                   `-- ...

    |  

    |-- system.slice

    |   |-- systemd-journald.service

    |   |-- systemd-udevd.service

    |   `-- ...

    |

    `-- user.slice

Sample setup cases

TODO something in the line of...

btrfs subvolume create /containers/www.example.com
yum -y --releasever=rawhide --nogpg --installroot=/containers/www.example.com --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal httpd
systemd-nspawn -bD /containers/www.example.com
....