core: optionally, accept a percentage value for MemoryLimit= and related settings

If a percentage is used, it is taken relative to the installed RAM size. This
should make it easier to write generic unit files that adapt to the local system.

1 files changed, 19 insertions, 17 deletions

diff --git a/man/systemd.resource-control.xml b/man/systemd.resource-control.xml
index d4c8fa7091..0551d75026 100644
--- a/man/systemd.resource-control.xml
+++ b/man/systemd.resource-control.xml
@@ -228,9 +228,11 @@
           reclaimed as long as memory can be reclaimed from unprotected units.</para>
 
           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
-          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. This controls the
-          <literal>memory.low</literal> control group attribute. For details about this control group attribute, see
-          <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
+          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
+          percentage value may be specified, which is taken relative to the installed physical memory on the
+          system. This controls the <literal>memory.low</literal> control group attribute. For details about this
+          control group attribute, see <ulink
+          url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 
           <para>Implies <literal>MemoryAccounting=true</literal>.</para>
 
@@ -247,7 +249,9 @@
           aggressively in such cases. This is the main mechanism to control memory usage of a unit.</para>
 
           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
-          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. If assigned the
+          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
+          percentage value may be specified, which is taken relative to the installed physical memory on the
+          system. If assigned the
           special value <literal>infinity</literal>, no memory limit is applied. This controls the
           <literal>memory.high</literal> control group attribute. For details about this control group attribute, see
           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
@@ -268,8 +272,9 @@
           last line of defense.</para>
 
           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
-          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. If assigned the
-          special value <literal>infinity</literal>, no memory limit is applied. This controls the
+          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
+          percentage value may be specified, which is taken relative to the installed physical memory on the system. If
+          assigned the special value <literal>infinity</literal>, no memory limit is applied. This controls the
           <literal>memory.max</literal> control group attribute. For details about this control group attribute, see
           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 
@@ -284,17 +289,14 @@
         <term><varname>MemoryLimit=<replaceable>bytes</replaceable></varname></term>
 
         <listitem>
-          <para>Specify the limit on maximum memory usage of the
-          executed processes. The limit specifies how much process and
-          kernel memory can be used by tasks in this unit. Takes a
-          memory size in bytes. If the value is suffixed with K, M, G
-          or T, the specified memory size is parsed as Kilobytes,
-          Megabytes, Gigabytes, or Terabytes (with the base 1024),
-          respectively. If assigned the special value
-          <literal>infinity</literal>, no memory limit is applied. This
-          controls the <literal>memory.limit_in_bytes</literal>
-          control group attribute. For details about this control
-          group attribute, see <ulink
+          <para>Specify the limit on maximum memory usage of the executed processes. The limit specifies how much
+          process and kernel memory can be used by tasks in this unit. Takes a memory size in bytes. If the value is
+          suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or
+          Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is
+          taken relative to the installed physical memory on the system. If assigned the special value
+          <literal>infinity</literal>, no memory limit is applied. This controls the
+          <literal>memory.limit_in_bytes</literal> control group attribute. For details about this control group
+          attribute, see <ulink
           url="https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt">memory.txt</ulink>.</para>
 
           <para>Implies <literal>MemoryAccounting=true</literal>.</para>