"free" shows far more memory usage than summing up application usage

kenneho · 08-06-2010, 03:46 AM

Hi all.

I've come across a really strange issue with one of my RHEL servers. The "free" command shows that 7019 MB of memory are actually in use by my system, but when summing up the actual usage (or even virtual usage like the example below) it doesn't add up - the sum is far less than what is reported by "free":

Code:

[root@server1 ~]# free -m 
             total       used       free     shared    buffers     cached 
Mem:         12011       7946       4065          0          4         23 
-/+ buffers/cache:       7919       4092 
Swap:         2015          0       2015 
[root@server1 ~]# ps -eo vsz|awk '{sum+=$1}END{print sum}'|xargs -I{} expr "{}" / 1024 
2611

Does anyone know what may be causing this? I'm really puzzled by this.

- kenneho

johnsfine · 08-06-2010, 07:32 AM

Is that a virtual machine or slice hosted by some service (as opposed to Linux running directly on the hardware)?

There are lots of reasons why used memory might be dominated by things other than ordinary process, but in a physical system it is very unlikely that cache and buffers would be so low while free is reasonable.

If this is some kind of slice or incompletely virtual system, then this kind of analysis of memory use is not the same as it would be for a whole system.

kenneho · 08-06-2010, 07:56 AM

Quote:

Originally Posted by johnsfine

Is that a virtual machine or slice hosted by some service (as opposed to Linux running directly on the hardware)?

There are lots of reasons why used memory might be dominated by things other than ordinary process, but in a physical system it is very unlikely that cache and buffers would be so low while free is reasonable.

If this is some kind of slice or incompletely virtual system, then this kind of analysis of memory use is not the same as it would be for a whole system.

Thanks for your reply.

It is in fact a virtual server running on Vmware ESX. I did some digging, and found that the VM was set up with 12 GB of RAM, but had some memory resource limit set to half a GB or something. When checking "unlimited" on the memory resource, and then rebooting, everything was back to normal.

But I still don't understand why the linux box would say that it had used 8 GB of memory. When rebooting it (before the fix) it consumed the 8 GB in a matter of minutes just like a serious memory leak. I mean; if the linux box shares the same iron as other linux'es, I don't see why the linux itself would see an increase in used memory. Any thought on this?

- kenneho