[Doc] add memory suggestion (#454)

add Direct Memory example and suggestion

Co-authored-by: Karen Metts <[email protected]>
Co-authored-by: Rob Bavey <[email protected]>
Co-authored-by: Ry Biesemeyer <[email protected]>

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 6.4.1
+  - [DOC] Add direct memory example [#454](https://github.com/logstash-plugins/logstash-input-beats/pull/454)
+
 ## 6.4.0
  - Feat: review and deprecate ssl protocol/cipher settings [#450](https://github.com/logstash-plugins/logstash-input-beats/pull/450)
 

VERSION

@@ -1 +1 @@
-6.4.0
+6.4.1

docs/index.asciidoc

@@ -88,6 +88,19 @@ will be similar to events directly indexed by {plugin-uc} into Elasticsearch.
 endif::[]
 
 
+[id="plugins-{type}s-{plugin}-memory"]
+===== Memory usage
+
+This plugin uses "off-heap" direct memory in addition to heap memory.
+By default, a JVM's off-heap direct memory limit is the same as the heap size.
+For example, setting `-Xmx10G` without setting the direct memory limit will allocate `10GB` for heap and an additional `10GB` for direct memory, for a total of `20GB` allocated. 
+You can set the amount of direct memory with `-XX:MaxDirectMemorySize` in {logstash-ref}/jvm-settings.html[Logstash JVM Settings]. 
+Consider setting direct memory to half of the heap size. 
+Setting direct memory too low decreases the performance of ingestion.
+
+NOTE: Be sure that heap and direct memory combined does not exceed the total memory available on the server to avoid an OutOfDirectMemoryError
+
+
 //Content for Beats
 ifeval::["{plugin}"=="beats"]
 [id="plugins-{type}s-{plugin}-multiline"]
@@ -101,6 +114,7 @@ plugin] to handle multiline events. Doing so will result in the failure to start
 Logstash.
 endif::[]
 
+
 //Content for Beats
 ifeval::["{plugin}"=="beats"]
 [id="plugins-{type}s-{plugin}-versioned-indexes"]