Huge Pages & Memory Utilization

At times you may find that Unix machines are showing 100% memory utilized, however you may not be running anything on the machine .  This could happen for the following reasons:

1.       Zombie/defunct processes consuming memory

Command to find them if there any: ps aux | awk '{ print $8 " " $2 }' | grep -w Z

2.       Java processes consuming all the memory for several reasons (Eg : memory leaks, heap spaces consuming more memory than the physical RAM etc .. )

3.       Huge pages configured on the machine.

The 1^st & 2^nd points are common issues that you may want to look into as soon as an issue occurs. The 3^rd point is what we will be explaining here:

Look at a screen shot below of a linux machine that has nothing (No programs) running on it.

A description about Huge Pages: A large page is essentially a block of contiguous physical-memory addresses that are reserved for a process. These blocks of memory is blocked only for programs (user processes) running on the server.

 Here is how you can view information about huge pages:

If your applications are memory intensive then using huge pages is recommended. In a 64 bit Linux OS heaps as large as 80% of the available physical memory can be configured using huge pages.

References:

For Linux: http://www.mjmwired.net/kernel/Documentation/vm/hugetlbpage.txt

For Solaris: http://www.solarisinternals.com/wiki/index.php/Multiple_Page_Size_Support