topic Active Memory Problem in Operating System - Tru64 Unix

Active Memory Problem

amrelsayed — Mon, 06 Jun 2005 00:59:50 GMT

Hi All,

We are facing a strange problem on one of our GS80 server running Tru64 4.0G.

top utility shows actvie memory as 11GB out of total physical memoty 12GB on the
server. We tried to addup memory used by all processes on the server as shown by
ps aux command but it does not add up to 11G. So, can any body suggest why top
shows such a high active memory (& so low Free memory i.e. 200K). Is there any
kernel parameter which causes this behaviour of Tru64 4.0G?

Kindly, Check the attached output from Top Utility.

Best Regards,
Amr

Re: Active Memory Problem

Han Pilmeyer — Mon, 06 Jun 2005 02:11:28 GMT

It's not as simple as that. In your case, you are running Oracle. All those processes appear to have a similar memory size. Large parts of these processes are shared, e.g. the shared text of the Oracle binary and the Oracle SGA.

Your free memory may appear to be low because the system uses most memory that isn't used for processes for the buffer cache (UBC).

This is all normal system behavior. Do you have reason to believe that you have a memory problem?

Re: Active Memory Problem

amrelsayed — Wed, 08 Jun 2005 00:24:53 GMT

Hi Han,

thank you very much for your reply. kindly, suggest what kernal parameter can affect this behaviour.

Best Regards,

Amr

Re: Active Memory Problem

Mulgund — Wed, 08 Jun 2005 00:32:04 GMT

sysconfig -q proc
Will give you all the required memory settings for the system.

Re: Active Memory Problem

Han Pilmeyer — Wed, 08 Jun 2005 01:38:16 GMT

Parameters in the proc sub system won't change anything for this!

Typically, in V4 (only!), people that run Oracle would set vm:ubc_maxpercent to a low value, e.g. 10. They would do this to prevent double cache in both the Oracle SGA and the UBC. Note that if you do this there are several other parameters that you have to change at the same time (e.g. ubc_borrowpercent, ubc_minpercent, vm_ubcseqstartpercent, vm_ubcseqpercent) as these all work together. Please read the documentation and the sys_attrs_vm man page before you do this.

This will most likely show that you have more free memory. Please understand however that the situation you described in your original question does NOT indicate any problem by itself.

Upgrading to V5.1B (from V4.0G) would be a very good thing for NUMA systems such as your GS80.

Re: Active Memory Problem

amrelsayed — Wed, 08 Jun 2005 03:15:53 GMT

thank you to all your replys, and many thanks to Han.

Best Regards,
Amr

Re: Active Memory Problem

amrelsayed — Wed, 08 Jun 2005 03:17:02 GMT

many thanks