mirror of
https://github.com/systemd/systemd.git
synced 2024-12-22 17:35:35 +03:00
302 lines
15 KiB
XML
302 lines
15 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="sd_event_add_memory_pressure" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_event_add_memory_pressure</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>sd_event_add_memory_pressure</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>sd_event_add_memory_pressure</refname>
|
|
<refname>sd_event_source_set_memory_pressure_type</refname>
|
|
<refname>sd_event_source_set_memory_pressure_period</refname>
|
|
<refname>sd_event_trim_memory</refname>
|
|
|
|
<refpurpose>Add and configure an event source run as result of memory pressure</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
|
|
|
|
<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_add_memory_pressure</function></funcdef>
|
|
<paramdef>sd_event *<parameter>event</parameter></paramdef>
|
|
<paramdef>sd_event_source **<parameter>ret_source</parameter></paramdef>
|
|
<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
|
|
<paramdef>void *<parameter>userdata</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_set_memory_pressure_type</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
<paramdef>const char *<parameter>type</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_source_set_memory_pressure_period</function></funcdef>
|
|
<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
|
|
<paramdef>uint64_t <parameter>threshold_usec</parameter></paramdef>
|
|
<paramdef>uint64_t <parameter>window_usec</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>int <function>sd_event_trim_memory</function></funcdef>
|
|
<paramdef>void</paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para><function>sd_event_add_memory_pressure()</function> adds a new event source that is triggered
|
|
whenever memory pressure is seen. This functionality is built around the Linux kernel's <ulink
|
|
url="https://docs.kernel.org/accounting/psi.html">Pressure Stall Information (PSI)</ulink> logic.</para>
|
|
|
|
<para>Expects an event loop object as first parameter, and returns the allocated event source object in
|
|
the second parameter, on success. The <parameter>handler</parameter> parameter is a function to call when
|
|
memory pressure is seen, or <constant>NULL</constant>. The handler function will be passed the
|
|
<parameter>userdata</parameter> pointer, which may be chosen freely by the caller. The handler may return
|
|
negative to signal an error (see below), other return values are ignored. If
|
|
<parameter>handler</parameter> is <constant>NULL</constant>, a default handler that compacts allocation
|
|
caches maintained by <filename>libsystemd</filename> as well as glibc (via <citerefentry
|
|
project='man-pages'><refentrytitle>malloc_trim</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
|
|
will be used.</para>
|
|
|
|
<para>To destroy an event source object use
|
|
<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
|
|
but note that the event source is only removed from the event loop when all references to the event
|
|
source are dropped. To make sure an event source does not fire anymore, even if it is still referenced,
|
|
disable the event source using
|
|
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
|
|
with <constant>SD_EVENT_OFF</constant>.</para>
|
|
|
|
<para>If the second parameter of <function>sd_event_add_memory_pressure()</function> is
|
|
<constant>NULL</constant> no reference to the event source object is returned. In this case the event
|
|
source is considered "floating", and will be destroyed implicitly when the event loop itself is
|
|
destroyed.</para>
|
|
|
|
<para>The event source will fire according to the following logic:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>If the
|
|
<varname>$MEMORY_PRESSURE_WATCH</varname>/<varname>$MEMORY_PRESSURE_WRITE</varname> environment
|
|
variables are set at the time the event source is established, it will watch the file, FIFO or AF_UNIX
|
|
socket specified via <varname>$MEMORY_PRESSURE_WATCH</varname> (which must contain an absolute path
|
|
name) for <constant>POLLPRI</constant> (in case it is a regular file) or <constant>POLLIN</constant>
|
|
events (otherwise). After opening the inode, it will write the (decoded) Base64 data provided via
|
|
<varname>$MEMORY_PRESSURE_WRITE</varname> into it before it starts polling on it (the variable may be
|
|
unset in which case this is skipped). Typically, if used, <varname>$MEMORY_PRESSURE_WATCH</varname>
|
|
will contain a path such as <filename>/proc/pressure/memory</filename> or a path to a specific
|
|
<filename>memory.pressure</filename> file in the control group file system
|
|
(cgroupfs).</para></listitem>
|
|
|
|
<listitem><para>If these environment variables are not set, the local PSI interface file
|
|
<filename>memory.pressure</filename> of the control group the invoking process is running in is
|
|
used.</para></listitem>
|
|
|
|
<listitem><para>If that file does not exist, the system-wide PSI interface file
|
|
<filename>/proc/pressure/memory</filename> is watched instead.</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>Or in other words: preferably any explicit configuration passed in by an invoking service manager
|
|
(or similar) is used as notification source, before falling back to local notifications of the service,
|
|
and finally to global notifications of the system.</para>
|
|
|
|
<para>Well-behaving services and applications are recommended to react to memory pressure events by
|
|
executing one or more of the following operations, in order to ensure optimal behaviour even on loaded
|
|
and resource-constrained systems:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>Release allocation caches such as <function>malloc_trim()</function> or similar, both
|
|
implemented in the libraries consumed by the program and in private allocation caches of the program
|
|
itself.</para></listitem>
|
|
|
|
<listitem><para>Release any other form of in-memory caches that can easily be recovered if
|
|
needed (e.g. browser caches).</para></listitem>
|
|
|
|
<listitem><para>Terminate idle worker threads or processes, or similar.</para></listitem>
|
|
|
|
<listitem><para>Even exit entirely from the program if it is idle and can be automatically started when
|
|
needed (for example via socket or bus activation).</para></listitem>
|
|
</itemizedlist>
|
|
|
|
<para>Any of the suggested operations should help easing memory pressure situations and allowing the
|
|
system to make progress by reclaiming the memory for other purposes.</para>
|
|
|
|
<para>This event source typically fires on memory pressure stalls, i.e. when operational latency above a
|
|
configured threshold already has been seen. This should be taken into consideration when discussing
|
|
whether later latency to re-aquire any released resources is acceptable: it's usually more important to
|
|
think of the latencies that already happened than those coming up in future.</para>
|
|
|
|
<para>The <function>sd_event_source_set_memory_pressure_type()</function> and
|
|
<function>sd_event_source_set_memory_pressure_period()</function> functions can be used to fine-tune the
|
|
PSI parameters for pressure notifications. The former takes either <literal>some</literal>,
|
|
<literal>full</literal> as second parameter, the latter takes threshold and period times in microseconds
|
|
as parameters. For details about these three parameters see the PSI documentation. Note that these two
|
|
calls must be invoked immediately after allocating the event source, as they must be configured before
|
|
polling begins. Also note that these calls will fail if memory pressure parameterization has been passed
|
|
in via the <varname>$MEMORY_PRESSURE_WATCH</varname>/<varname>$MEMORY_PRESSURE_WRITE</varname>
|
|
environment variables (or in other words: configuration supplied by a service manager wins over internal
|
|
settings).</para>
|
|
|
|
<para>The <function>sd_event_trim_memory()</function> function releases various internal allocation
|
|
caches maintained by <filename>libsystemd</filename> and then invokes glibc's <citerefentry
|
|
project='man-pages'><refentrytitle>malloc_trim</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
|
|
makes the operation executed when the handler function parameter of
|
|
<function>sd_event_add_memory_pressure</function> is passed as <constant>NULL</constant> directly
|
|
accessible for invocation at any time (see above). This function will log a structured log message at
|
|
<constant>LOG_DEBUG</constant> level (with message ID f9b0be465ad540d0850ad32172d57c21) about the memory
|
|
pressure operation.</para>
|
|
|
|
<para>For further details see <ulink url="https://systemd.io/MEMORY_PRESSURE">Memory Pressure Handling in
|
|
systemd</ulink>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Return Value</title>
|
|
|
|
<para>On success, these functions return 0 or a positive
|
|
integer. On failure, they return a negative errno-style error
|
|
code.</para>
|
|
|
|
<refsect2>
|
|
<title>Errors</title>
|
|
|
|
<para>Returned errors may indicate the following problems:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><constant>-ENOMEM</constant></term>
|
|
|
|
<listitem><para>Not enough memory to allocate an object.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EINVAL</constant></term>
|
|
|
|
<listitem><para>An invalid argument has been passed.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EHOSTDOWN</constant></term>
|
|
|
|
<listitem><para>The <varname>$MEMORY_PRESSURE_WATCH</varname> variable has been set to the literal
|
|
string <filename>/dev/null</filename>, in order to explicitly disable memory pressure
|
|
handling.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EBADMSG</constant></term>
|
|
|
|
<listitem><para>The <varname>$MEMORY_PRESSURE_WATCH</varname> variable has been set to an invalid
|
|
string, for example a relative rather than an absolute path.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-ENOTTY</constant></term>
|
|
|
|
<listitem><para>The <varname>$MEMORY_PRESSURE_WATCH</varname> variable points to a regular file
|
|
outside of the procfs or cgroupfs file systems.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EOPNOTSUPP</constant></term>
|
|
|
|
<listitem><para>No configuration via <varname>$MEMORY_PRESSURE_WATCH</varname> has been specified
|
|
and the local kernel does not support the PSI interface.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EBUSY</constant></term>
|
|
|
|
<listitem><para>This is returned by <function>sd_event_source_set_memory_pressure_type()</function>
|
|
and <function>sd_event_source_set_memory_pressure_period()</function> if invoked on event sources
|
|
at a time later than immediately after allocating them.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-ESTALE</constant></term>
|
|
|
|
<listitem><para>The event loop is already terminated.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-ECHILD</constant></term>
|
|
|
|
<listitem><para>The event loop has been created in a different process, library or module instance.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><constant>-EDOM</constant></term>
|
|
|
|
<listitem><para>The passed event source is not a signal event source.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v254"/></listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" />
|
|
|
|
<refsect1>
|
|
<title>History</title>
|
|
<para><function>sd_event_add_memory_pressure()</function>,
|
|
<function>sd_event_source_set_memory_pressure_type()</function>,
|
|
<function>sd_event_source_set_memory_pressure_period()</function>, and
|
|
<function>sd_event_trim_memory()</function> were added in version 254.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
|
|
<para><simplelist type="inline">
|
|
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
</simplelist></para>
|
|
</refsect1>
|
|
|
|
</refentry>
|