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core: introduce MemoryTHP= unit file setting

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Transparent Hugepages (THP) is a Linux kernel feature that manages
memory using larger pages (2MB on x86, compared to the default 4KB).
The main goal is to improve memory management efficiency and system
performance, especially for memory-intensive applications.
However, it can cause drawbacks in some scenarios, such as memory
regression and latency spikes. THP policy is governed for the entire
system via /sys/kernel/mm/transparent_hugepage/enabled.
However, it can be overridden for individual workloads via prctl(2)
call.
MemoryTHP= is used to disable THPs at exec-invoke to stop
providing THPs for workloads where the drawbacks outweigh the advantages.
When set to "disable", MemoryTHP= disables THPs completely for the
process, irrespecitive of global THP controls.
When set to "madvise", MemoryTHP= disables THPs for the process except
when specifically madvised by the process with MADV_HUGEPAGE or MADV_COLLAPSE.
This commit is contained in:
Usama Arif
2026-01-06 03:26:14 -08:00
parent 9573ad4e76
commit 32614b9aab
18 changed files with 164 additions and 6 deletions
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man/systemd.exec.xml
+35
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@@ -2134,6 +2134,41 @@ BindReadOnlyPaths=/var/lib/systemd</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>MemoryTHP=</varname></term>
<listitem><para>Transparent Hugepages (THPs) is a Linux kernel feature that manages memory
using larger pages (2MB on x86, compared to the default 4KB). The main goal is to improve memory management
efficiency and system performance, especially for memory-intensive applications.
However, it can cause drawbacks in some scenarios, such as memory regression and latency spikes.
THP policy is governed for the entire system via <filename>/sys/kernel/mm/transparent_hugepage/enabled</filename>.
However, it can be overridden for individual workloads via
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
<varname>MemoryTHP=</varname> may be used to disable THPs at process invocation time to stop providing
THPs for workloads where the drawbacks outweigh the advantages.
When <varname>MemoryTHP=</varname> is set to <literal>inherit</literal> or not set at all, systemd
inherits THP settings from the process that starts it and no
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
<constant>PR_SET_THP_DISABLE</constant> call is made.
When set to <literal>disable</literal>, <varname>MemoryTHP=</varname> disables THPs completely for the process,
irrespecitive of global THP controls.
When set to <literal>madvise</literal>, <varname>MemoryTHP=</varname> disables THPs for the process except when
specifically requested via <citerefentry><refentrytitle>madvise</refentrytitle><manvolnum>2</manvolnum></citerefentry>
by the process with <constant>MADV_HUGEPAGE</constant> or <constant>MADV_COLLAPSE</constant>.
When set to <literal>system</literal>, <varname>MemoryTHP=</varname> resets the THP policy to system wide policy.
This can be used when the process that starts systemd has already disabled THPs via
<constant>PR_SET_THP_DISABLE</constant>, and we want to restore the system default THP setting at
process invokation time. For details, see
<ulink url="https://docs.kernel.org/admin-guide/mm/transhuge.html">Transparent Hugepage Support</ulink>
in the kernel documentation.</para>
<para>Note that this functionality might not be available, for example if THP is disabled in the
kernel, or the kernel does not support controlling THP at the process level through
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.</para>
<xi:include href="version-info.xml" xpointer="v260"/>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivatePIDs=</varname></term>