Document `memory_limit` option.

ChangeLog.txt

@@ -1,8 +1,11 @@
 1.6.1 - 201905xx
 ================
 
+Broker:
+- Document `memory_limit` option.
+
 Clients:
-- Fix compilation on musl C systems due to missing sys/time.h header.
+- Fix compilation on non glibc systems due to missing sys/time.h header.
 
 
 1.6 - 20190417

man/mosquitto.conf.5.xml

@@ -588,9 +588,27 @@ log_timestamp_format %Y-%m-%dT%H:%M:%S
 					<para>Reloaded on reload signal.</para>
 				</listitem>
 			</varlistentry>
+			<varlistentry>
+				<term><option>memory_limit</option> <replaceable>limit</replaceable></term>
+				<listitem>
+                    <para>
+						This option sets the maximum number of heap memory bytes that the broker
+						will allocate, and hence sets a hard limit on memory use by the broker.
+						Memory requests that exceed this value will be denied. The effect will
+						vary depending on what has been denied. If an incoming message is being
+						processed, then the message will be dropped and the publishing client
+						will be disconnected. If an outgoing message is being sent, then the
+						individual message will be dropped and the receiving client will be
+						disconnected. Defaults to no limit.</para>
+					<para>This option is only available if memory tracking support is compiled
+						in.</para>
+					<para>Reloaded on reload signal. Setting to a lower value and reloading will
+						not result in memory being freed.</para>
+				</listitem>
+			</varlistentry>
 			<varlistentry>
 				<term><option>message_size_limit</option> <replaceable>limit</replaceable></term>
-				<listitem> 
+				<listitem>
 					<para>This option sets the maximum publish payload size
 						that the broker will allow. Received messages that
 						exceed this size will not be accepted by the broker.

mosquitto.conf

@@ -194,6 +194,16 @@
 #max_packet_size 0
 
 
+# This option sets the maximum number of heap memory bytes that the broker will
+# allocate, and hence sets a hard limit on memory use by the broker.  Memory
+# requests that exceed this value will be denied. The effect will vary
+# depending on what has been denied. If an incoming message is being processed,
+# then the message will be dropped and the publishing client will be
+# disconnected. If an outgoing message is being sent, then the individual
+# message will be dropped and the receiving client will be disconnected.
+# Defaults to no limit.
+#memory_limit 0
+
 # =================================================================
 # Default listener
 # =================================================================