cgroups.7: Document the cgroups v2 'memory_localevents' mount option

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/cgroups.7

@@ -626,6 +626,21 @@ can be specified when mounting the group v2 filesystem:
 .IR nsdelegate " (since Linux 4.15)"
 Treat cgroup namespaces as delegation boundaries.
 For details, see below.
+.TP
+.IR memory_localevents " (since Linux 5.2)"
+.\" commit 9852ae3fe5293264f01c49f2571ef7688f7823ce
+The
+.I memory.events
+should show statistics only for the cgroup itself,
+and not for any descendant cgroups.
+This was the behavior before Linux 5.2.
+Starting in Linux 5.2,
+the default behavior is to include statistics for descendant cgroups in
+.IR memory.events ,
+and this mount option can be used to revert to the legacy behavior.
+This option is system wide and can be set on mount or
+modified through remount only from the initial mount namespace;
+it is silently ignored in noninitial namespaces.
 .\"
 .SS Cgroups v2 controllers
 The following controllers, documented in the kernel source file
@@ -1793,12 +1808,18 @@ Features are listed one per line:
 .EX
 $ \fBcat /sys/kernel/cgroup/features\fP
 nsdelegate
+memory_localevents
 .EE
 .in
 .IP
 The entries that can appear in this file are:
 .RS
 .TP
+.IR memory_localevents " (since Linux 5.2)"
+The kernel supports the
+.I memory_localevents
+mount option.
+.TP
 .IR nsdelegate " (since Linux 4.15)"
 The kernel supports the
 .I nsdelegate