diff --git a/man/systemd.xml b/man/systemd.xml
index 77aade8158..b166e534a5 100644
--- a/man/systemd.xml
+++ b/man/systemd.xml
@@ -392,6 +392,25 @@
systemd.special7
for details about these target units.
+ systemd only keeps a minimal set of units loaded into memory. Specifically, the only units that are kept
+ loaded into memory are those for which at least one of the following conditions is true:
+
+
+ It is in an active, activating, deactivating or failed state (i.e. in any unit state except for dead)
+ It has a job queued for it
+ It is a dependency of some sort of at least one other unit that is loaded into memory
+ It has some form of resource still allocated (e.g. a service unit that is inactive but for which
+ a process is still lingering that ignored the request to be terminated)
+ It has been pinned into memory programmatically by a D-Bus call
+
+
+ systemd will automatically and implicitly load units from disk — if they are not loaded yet — as soon as
+ operations are requested for them. Thus, in many respects, the fact whether a unit is loaded or not is invisible to
+ clients. Use systemctl list-units --all to comprehensively list all units currently loaded. Any
+ unit for which none of the conditions above applies is promptly unloaded. Note that when a unit is unloaded from
+ memory its accounting data is flushed out too. However, this data is generally not lost, as a journal log record
+ is generated declaring the consumed resources whenever a unit shuts down.
+
Processes systemd spawns are placed in individual Linux
control groups named after the unit which they belong to in the
private systemd hierarchy. (see