Robert Nichols wrote:

On 07/20/2011 02:56 PM, Michael McNulty wrote:

...

Can someone help clear up some confusion in reading memory usage in Top and System monitor. Here is a picture of both. http://s1176.photobucket.com/albums/x327/ionosphere2011/ mailto:centos@centos.org

Why does "System Monitor" show 1.7gb free out of 8gb. While Top shows all 8gb being used? If 1.7gb is free then it should not be using swap space so I assume "System Monitor" is reporting it incorrectly?

Take a look at the output from the 'free' command. In the first line of memory usage numbers, buffer memory and cache memory is included in the "used" category. For the numbers in the "+/- buffers/cache" line, buffer and cache memory is considered "free" since it can easily be used to satisfy memory requests. The 'top' command shows just that first set of numbers. System Monitor shows the more meaningful number from the second line.

Linux kernel uses available memory for caching. If needed, it will use 100% of free memory for caching. Cached data is stored for faster retrieval of applications, but can in any time be disposed of in favor of memory for applications.

Different apps will report memory usage differently because different people perceive definition of free memory in different ways.

If you place System Monitor on the panel you will see two colors, dark is memory used for/by applications, and above it will be light color (green is default) that represents cached data.