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diff --git a/man/systemd-oomd.service.xml b/man/systemd-oomd.service.xml new file mode 100644 index 0000000..9cb9c60 --- /dev/null +++ b/man/systemd-oomd.service.xml @@ -0,0 +1,98 @@ +<?xml version='1.0'?> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> +<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> + +<refentry id="systemd-oomd.service" conditional='ENABLE_OOMD'> + + <refentryinfo> + <title>systemd-oomd.service</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>systemd-oomd.service</refentrytitle> + <manvolnum>8</manvolnum> + </refmeta> + + <refnamediv> + <refname>systemd-oomd.service</refname> + <refname>systemd-oomd</refname> + <refpurpose>A userspace out-of-memory (OOM) killer</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <para><filename>systemd-oomd.service</filename></para> + <para><filename>/usr/lib/systemd/systemd-oomd</filename></para> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para><command>systemd-oomd</command> is a system service that uses cgroups-v2 and pressure stall information (PSI) + to monitor and take action on processes before an OOM occurs in kernel space.</para> + + <para>You can enable monitoring and actions on units by setting <varname>ManagedOOMSwap=</varname> and/or + <varname>ManagedOOMMemoryPressure=</varname> to the appropriate value. <command>systemd-oomd</command> will + periodically poll enabled units' cgroup data to detect when corrective action needs to occur. When an action needs + to happen, it will only be performed on the descendant cgroups of the enabled units. More precisely, only cgroups with + <filename>memory.oom.group</filename> set to <constant>1</constant> and leaf cgroup nodes are eligible candidates. + Action will be taken recursively on all of the processes under the chosen candidate.</para> + + <para>See + <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for more information about the configuration of this service.</para> + </refsect1> + + <refsect1> + <title>Setup Information</title> + + <para>The system must be running systemd with a full unified cgroup hierarchy for the expected cgroups-v2 features. + Furthermore, resource accounting must be turned on for all units monitored by <command>systemd-oomd</command>. + The easiest way to turn on resource accounting is by ensuring the values for <varname>DefaultCPUAccounting</varname>, + <varname>DefaultIOAccounting</varname>, <varname>DefaultMemoryAccounting</varname>, and + <varname>DefaultTasksAccounting</varname> are set to <constant>true</constant> in + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> + + <para>You will need a kernel compiled with PSI support. This is available in Linux 4.20 and above.</para> + + <para>The system must also have swap enabled for <command>systemd-oomd</command> to function correctly. With swap + enabled, the system spends enough time swapping pages to let <command>systemd-oomd</command> react. + Without swap, the system enters a livelocked state much more quickly and may prevent <command>systemd-oomd</command> + from responding in a reasonable amount of time. See + <ulink url="https://chrisdown.name/2018/01/02/in-defence-of-swap.html">"In defence of swap: common misconceptions"</ulink> + for more details on swap.</para> + + <para>Be aware that if you intend to enable monitoring and actions on <filename>user.slice</filename>, + <filename>user-$UID.slice</filename>, or their ancestor cgroups, it is highly recommended that your programs be + managed by the systemd user manager to prevent running too many processes under the same session scope (and thus + avoid a situation where memory intensive tasks trigger <command>systemd-oomd</command> to kill everything under the + cgroup). If you're using a desktop environment like GNOME, it already spawns many session components with the + systemd user manager.</para> + </refsect1> + + <refsect1> + <title>Usage Recommendations</title> + + <para><varname>ManagedOOMSwap=</varname> works with the system-wide swap values, so setting it on the root slice + <filename>-.slice</filename>, and allowing all descendant cgroups to be eligible candidates may make the most + sense.</para> + + <para><varname>ManagedOOMMemoryPressure=</varname> tends to work better on the cgroups below the root slice + <filename>-.slice</filename>. For units which tend to have processes that are less latency sensitive (e.g. + <filename>system.slice</filename>), a higher limit like the default of 60% may be acceptable, as those processes + can usually ride out slowdowns caused by lack of memory without serious consequences. However, something like + <filename>user@$UID.service</filename> may prefer a much lower value like 40%.</para> + </refsect1> + + <refsect1> + <title>See Also</title> + <para> + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>oomctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> + </para> + </refsect1> +</refentry> |