How is memory calculated when Solarwinds agent is used for Linux servers

The Linux Agent polls memory statistics from the /proc filesystem (/proc/meminfo) as follows:

and another question... if i check Memory in console for 1 server in gauge, it shows different % and different for physical memory... m referring this for agent based only...  when m alerting using percent memory variable which one will it refer?

and another question... if i check Memory in console for 1 server in gauge, it shows different % and different for physical memory... m referring this for agent based only...  when m alerting using percent memory variable which one will it refer?

Some tools consider items such as cache to be used memory. This is how NET-SNMP calculates memory used, and this is not typically what most people would consider to be accurate. That is because the Linux operating system will use any/all available memory for disk cache until such time as it is needed for an application. Then that memory is released and made available for use by whichever application is in need of that RAM. 

but for alerting how does it work? there is percent memory used option.. so what does this take into account? like i said overall memory is different and physical memory is different...

Alerting uses the same values displayed within the Orion web interface for that node. 

aLTeReGo below example of one Linux server monitored via agent...

Now in this how does it relate? Memory used in gauge states 7% whereas Physical Memory shows 21%... am i missing somethning?

List resouces info incase m doing something wrong:

Just look at physical memory utilization and swap utilization.  those are the numbers that are going to be meaningful and actionable.

The node' memory usage show in the radial gauge is showing actual Memory Used, excluding cache memory. Because this is a volatile cache that is used dynamically and surrendered when applications need that additional memory to function properly, most people would not consider that to be 'used'. At least not in the sense that undue memory pressure is occurring on the system that needs to be addressed. 

The 'Physical Memory' volume, shown as a linear gauge in your screenshot above, is showing the actual amount of physical memory consumed, irrespective of what that memory is used for. 

You can choose to alert on either (or both) of these metrics in Orion depending upon what you are concerned with. Most people simply choose to use Node Memory Utilization, as that is the value most representative of a problem with memory preasure on the system. 

it should match when trying to check on device also right.. thats the main reason i was trying to find out the formula info...let me check