Oak TarMK memory mapped files

Hi guys.

Lately I am trying to investigate Oak feature that exploits direct memory (off-heap memory) to increase performance [1] [2] [3]. As far as I have understood, besides memory assigned to AEM through JVM heap, Oak uses off-heap memory as well. In order to actually make use of this feature I have set the following JVM parameters:

/usr/java/jdk1.8.0_40/bin/java -server -Xms5120m -Xmx5120m -XX:MaxDirectMemorySize=5120m -XX:PermSize=512m -XX:MaxPermSize=512m

Total memory is 12 G, so the idea was: taking out 2 G from total (operative systems, etc...), 50% to AEM max heap (5 G), and the other 50% (5 G) free to be used, hopefully, by Oak through direct memory. I have also set this -XX:MaxDirectMemorySize=5120m to explicitely set max direct memory.

Now my doubt is: how can I be sure that those free 5 G of memory are really used by Oak? How can I monitor and trace this? How can I compare performances?

Java version 1.8

AEM 6.0 + SP3 running on Unix64 bit

OAK version is 1.0.22

Total memory is 12 G

[1] https://www.terrabeata.com/2015/03/think-outside-the-heap-with-aem-6-and-jackrabbit-oak-tarmk/

[2] http://www.pro-vision.de/content/dam/pro-vision/production/adaptto/2013/adaptto2013-oak-for-users-michael-marth-pdf.pdf/_jcr_content/renditions/original./adaptto2013-oak-for-users-michael-marth-pdf.pdf (slide 17)

[3] http://www.slideshare.net/AEMHub2014/oak-michael-marth (slide 10)

Thank you