understanding the output of "free"

m4rtin · 06-29-2011, 03:25 PM

I have a small server with following memory usage:

Code:

root@debian:~# free -m
             total       used       free     shared    buffers     cached
Mem:          2003       1822        181          0         42        939
-/+ buffers/cache:        840       1163
Swap:         2379          0       2379
root@debian:~#

I have 2048MB of RAM in server. As I understand, 2003MB is the amount of memory what is left of this 2048MB after kernel reserved 45MB during the bootup. The third line regarding swap is clear as well(results overlap with swapon -s). In addition, if I'm not wrong, only 181MB of RAM is totally unused.

I'm aware of that Linux uses free memory for buffers, but how to find out how much memory is in use for applications? Is it 2003MB-181MB-840MB= 982MB?

business_kid · 06-29-2011, 03:28 PM

The docs do say that free is less than perfect. Try top, or as you have a server, get some more serious profiling tools. BTW I've just posted a query about it on the mobile forum.

m4rtin · 06-29-2011, 05:51 PM

Quote:

Originally Posted by business_kid

The docs do say that free is less than perfect. Try top, or as you have a server, get some more serious profiling tools. BTW I've just posted a query about it on the mobile forum.

Could you name some serious profiling tools for Linux server in order to analyze memory usage?

syg00 · 06-29-2011, 10:56 PM

Quote:

Originally Posted by m4rtin

I'm aware of that Linux uses free memory for buffers, but how to find out how much memory is in use for applications? Is it 2003MB-181MB-840MB= 982MB?

Nope - you could simply look at the free output

Code:

-/+ buffers/cache:        840       1163

All the maths has been done for you.

Of course that presupposes all the buffer/cache is not relevant to any app. Couldn't be more wrong, but a lot of people seem happy with that number.
Linux memory usage is a real can of worms - /proc/<pid>/smaps was added a while back to expose more of the data. Have a read of this - it includes a perl script as well.