Merge pull request #3843 from maxime1986/minor-systemd.resource-control

diff --cc man/systemd.resource-control.xml
index bf44a683451762c3d1f26b114f1022b13216e163,cb8c896e5ce2e15842beefcc8220102eddd68f70..0e98ca78b8f52d5af081a673659a7f5621473365
--- 1/man/systemd.resource-control.xml
--- 2/man/systemd.resource-control.xml
+++ b/man/systemd.resource-control.xml
@@@ -126,6 -127,13 +127,13 @@@
      settings of a unit for a given resource type are for the other hierarchy type, the settings are translated and
      applied. If there are any valid settings for the hierarchy in use, all translations are disabled for the resource
      type. Mixing the two types of settings on a unit can lead to confusing results.</para>
 -    doesn't allow safe delegation of controllers to unprivileged processes. If the system use legacy control group
+ 
+     <para>Legacy control group hierarchy (see <ulink
+     url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>), also called cgroup-v1,
++    doesn't allow safe delegation of controllers to unprivileged processes. If the system uses the legacy control group
+     hierarchy, resource control is disabled for systemd user instance, see
+     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
+     </para>
    </refsect1>
  
    <refsect1>