Monitoring Memory Performance

Unix processes are tracked from creation to termination by their process ID. Processes are grouped and queued by their process state. A processes may be in one of the following states; as displayed by the command ps:

O - Process is running on a processor.
S - Sleeping: process is waiting for an event to complete.
R - Runnable: process is on run queue.
Z - Zombie state: process terminated and parent not waiting.
T - Process is stopped, either by a job control signal or because it is being traced.

Sleeping processes may be moved out of physical memory to allow runnable process to execute. Paging or swapping is when the kernel moves parts or all of a process to virtual memory.

The HP-UX system provides the command swapinfo for a more complete review of the swap space usage and configuration. The SunOS 5.X and IRIX systems have the command swap -l. Linux offers the free command which displays amount of free and used memory for the system.

To interactively monitor virtual and real memory usage, the command vmstat available on all but the IRIX system, which duplicates the functionality with the command osview and the graphical based display gr_osview.

Please review the man page for more information on vmstat and osview command options and display output for the following systems.

Solaris 2.5 or SunOS 5.5
SGI IRIX 5.3
HP HP-UX 10.0
Linux

The top command can also be used, as a general tool, for discovering bottlenecks. It is distributed with SGI IRIX, HP HP-UX, and the Linux operating systems. The binary is available for Sun SunOS 2.5 from the Unix Workstation Support Group ftp server. Click here to download the Sun 5.5 top binary.

The top utility provides a full screen look at system statistics and a list of the most active processes on the system.

Terms used: kernel, virtual memory.