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Diffstat (limited to 'nixos/doc/manual/administration/control-groups.xml')
| -rw-r--r-- | nixos/doc/manual/administration/control-groups.xml | 84 |
1 files changed, 38 insertions, 46 deletions
diff --git a/nixos/doc/manual/administration/control-groups.xml b/nixos/doc/manual/administration/control-groups.xml index 0d7b8ae910a7..bb8b7f83d9e0 100644 --- a/nixos/doc/manual/administration/control-groups.xml +++ b/nixos/doc/manual/administration/control-groups.xml @@ -3,20 +3,18 @@ xmlns:xi="http://www.w3.org/2001/XInclude" version="5.0" xml:id="sec-cgroups"> - -<title>Control Groups</title> - -<para>To keep track of the processes in a running system, systemd uses -<emphasis>control groups</emphasis> (cgroups). A control group is a -set of processes used to allocate resources such as CPU, memory or I/O -bandwidth. There can be multiple control group hierarchies, allowing -each kind of resource to be managed independently.</para> - -<para>The command <command>systemd-cgls</command> lists all control -groups in the <literal>systemd</literal> hierarchy, which is what -systemd uses to keep track of the processes belonging to each service -or user session: - + <title>Control Groups</title> + <para> + To keep track of the processes in a running system, systemd uses + <emphasis>control groups</emphasis> (cgroups). A control group is a set of + processes used to allocate resources such as CPU, memory or I/O bandwidth. + There can be multiple control group hierarchies, allowing each kind of + resource to be managed independently. + </para> + <para> + The command <command>systemd-cgls</command> lists all control groups in the + <literal>systemd</literal> hierarchy, which is what systemd uses to keep + track of the processes belonging to each service or user session: <screen> $ systemd-cgls ├─user @@ -34,40 +32,34 @@ $ systemd-cgls │ └─2376 dhcpcd --config /nix/store/f8dif8dsi2yaa70n03xir8r653776ka6-dhcpcd.conf └─ <replaceable>...</replaceable> </screen> - -Similarly, <command>systemd-cgls cpu</command> shows the cgroups in -the CPU hierarchy, which allows per-cgroup CPU scheduling priorities. -By default, every systemd service gets its own CPU cgroup, while all -user sessions are in the top-level CPU cgroup. This ensures, for -instance, that a thousand run-away processes in the -<literal>httpd.service</literal> cgroup cannot starve the CPU for one -process in the <literal>postgresql.service</literal> cgroup. (By -contrast, it they were in the same cgroup, then the PostgreSQL process -would get 1/1001 of the cgroup’s CPU time.) You can limit a service’s -CPU share in <filename>configuration.nix</filename>: - + Similarly, <command>systemd-cgls cpu</command> shows the cgroups in the CPU + hierarchy, which allows per-cgroup CPU scheduling priorities. By default, + every systemd service gets its own CPU cgroup, while all user sessions are in + the top-level CPU cgroup. This ensures, for instance, that a thousand + run-away processes in the <literal>httpd.service</literal> cgroup cannot + starve the CPU for one process in the <literal>postgresql.service</literal> + cgroup. (By contrast, it they were in the same cgroup, then the PostgreSQL + process would get 1/1001 of the cgroup’s CPU time.) You can limit a + service’s CPU share in <filename>configuration.nix</filename>: <programlisting> -systemd.services.httpd.serviceConfig.CPUShares = 512; +<link linkend="opt-systemd.services._name_.serviceConfig">systemd.services.httpd.serviceConfig</link>.CPUShares = 512; </programlisting> - -By default, every cgroup has 1024 CPU shares, so this will halve the -CPU allocation of the <literal>httpd.service</literal> cgroup.</para> - -<para>There also is a <literal>memory</literal> hierarchy that -controls memory allocation limits; by default, all processes are in -the top-level cgroup, so any service or session can exhaust all -available memory. Per-cgroup memory limits can be specified in -<filename>configuration.nix</filename>; for instance, to limit -<literal>httpd.service</literal> to 512 MiB of RAM (excluding swap): - + By default, every cgroup has 1024 CPU shares, so this will halve the CPU + allocation of the <literal>httpd.service</literal> cgroup. + </para> + <para> + There also is a <literal>memory</literal> hierarchy that controls memory + allocation limits; by default, all processes are in the top-level cgroup, so + any service or session can exhaust all available memory. Per-cgroup memory + limits can be specified in <filename>configuration.nix</filename>; for + instance, to limit <literal>httpd.service</literal> to 512 MiB of RAM + (excluding swap): <programlisting> -systemd.services.httpd.serviceConfig.MemoryLimit = "512M"; +<link linkend="opt-systemd.services._name_.serviceConfig">systemd.services.httpd.serviceConfig</link>.MemoryLimit = "512M"; </programlisting> - -</para> - -<para>The command <command>systemd-cgtop</command> shows a -continuously updated list of all cgroups with their CPU and memory -usage.</para> - + </para> + <para> + The command <command>systemd-cgtop</command> shows a continuously updated + list of all cgroups with their CPU and memory usage. + </para> </chapter> |