This article will provide you with a quick reference guide on how to calculate the Java process size memory footprint for Java VM processes running on IBM AIX 5.3+ OS.
This is a complementary post to my original article on this subject: how to monitor the Java native memory on AIX. I highly recommend this read to any individual involved in production support or development of Java applications deployed on AIX.
Why is this knowledge important?
From my perspective, basic knowledge on how the OS is managing the memory allocation of your JVM processes is very important. We often overlook this monitoring aspect and only focus on the Java heap itself.
From my experience, most Java memory related problems are observed from the Java heap itself such as garbage collection problems, leaks etc. However, I’m confident that you will face situations in the future involving native memory problems or OS memory challenges. Proper knowledge of your OS and virtual memory management is crucial for proper root causes analysis, recommendations and solutions.
AIX memory vs. pages
As you may have seen from my earlier post, the AIX Virtual Memory Manager (VMM) is responsible to manage memory requests from the system and its applications.
The actual physical memory is converted and partitioned in units called pages; allocated either in physical RAM or stored on disk until it is needed. Each page can have a size of 4 KB (small page), 64 KB (medium page) or 16 MB (large page). Typically for a 64-bit Java process you will see a mix of all of the above.
What about the topas command?
The typical reflex when supporting applications on AIX is to run the topas command, similar to Solaris top. Find below an example of output from AIX 5.3:
As you can see, the topas command is not very helpful to get a clear view on the memory utilization since it is not providing the breakdown view that we need for our analysis. It is still useful to get a rough idea of the paging space utilization which can give you a quick idea of your top "paging space" consumer processes. Same can be achieved via the ps aux command.
AIX OS command to the rescue: svmon
The AIX svmon command is by far my preferred command to deep dive into the Java process memory utilization. This is a very powerful command, similar to Solaris pmap. It allows you to monitor the current memory “pages” allocation along with each segment e.g. Java Heap vs. native heap segments. Analyzing the svmon output will allow you to calculate the memory footprint for each page type (4 KB, 64 KB, and 16 MB).
# 64-bit JVM with -Xms2048m & -Xmx2048m (2 GB Java Heap)
I hope this article has helped you to understand how to calculate the Java process size on AIX OS. Please feel free to post any comment or question.