Am I short of memory for the JVMs ?

[Krist]

Hi all,

In our apps server, we are running 4 JVMs with the following
settings :

JVM_1 : -ms3072M -mx3072M -XX:MaxPermSize=1024M
JVM_2 : -ms3072M -mx3072M -XX:MaxPermSize=1024M
JVM_3 : -ms1024M -mx1536M -XX:MaxPermSize=1024M
JVM_4 : -ms128M -mx128M -XX:MaxPermSize=128M

We are running on 12 GB memory and 2 CPU Xeon dualcore and Redhat 4.

During peak load, when I type free -m command from Linux , the output
is :

Mem total : 12010 used : 11988 free : 21
Swap total : 4096 used : 0 free : 4096
( no matter how long, the swap is never used by the system )

Based on this , am I running short of memory ?

Thank you,
xtanto

 

[Martin Gregorie]

Hi all,

In our apps server, we are running 4 JVMs with the following settings :

JVM_1 : -ms3072M -mx3072M -XX:MaxPermSize=1024M JVM_2 : -ms3072M
-mx3072M -XX:MaxPermSize=1024M JVM_3 : -ms1024M -mx1536M
-XX:MaxPermSize=1024M JVM_4 : -ms128M -mx128M -XX:MaxPermSize=128M

We are running on 12 GB memory and 2 CPU Xeon dualcore and Redhat 4.

During peak load, when I type free -m command from Linux , the output is
:

Mem total : 12010 used : 11988 free : 21 Swap total : 4096
used : 0 free : 4096 ( no matter how long, the swap is never
used by the system )

Based on this , am I running short of memory ?

Its not swapping, so its probably happy.

The only thing I notice is that there's only 21 MB left for disk
buffering, etc. Are you noticing slow I/O or reduced network throughput?
Have you used sar or other monitoring tools to examine system operation?

 

[Krist]

This output of 'free -m' is incomplete. It should look like this:

             total       used       free     shared    buffers     cached
Mem:          7937       1916       6021          0        197        849
-/+ buffers/cache:        869       7068
Swap:        30513          0      30513

Note that there are _two_ 'free' numbers for RAM (not counting swap). On
the first line, this is the totally unused RAM. On the second line, this
is the sum of that unused RAM and the RAM currently used to cache disk
data. Here, my PC is rather freshly rebooted so there are 6 GB
untouched, but already 1 GB used for disk cache. RAM used as a disk
cache can be freed immediately, so it is "kind-of-free".

The amount of unused RAM should gradually lower, down to a small
proportion of the total RAM, while the computer is up (it does not reach
zero because the kernel keeps a bit of unused RAM for some emergency
cases deep within the kernel itself). I guess that the '21' above is the
amount of unused RAM, and it is not a concern.

        --Thomas Pornin

Hi Thomas,
Thanks for your reply.
The complete output is like this :

total used free shared buffers
cached
Mem: 12010 11980 30 0 149
2326
-/+ buffers/cache: 9504 2505
Swap: 4095 0 4095

Does it mean actually there is still 2505+30 kb Free = 2.5 GB ??

Thank you,
Krist