memory utilization on N class

[Jason Berendsen]

We have broken down our memory utilization on an N class server that is memory constrained utilizing TOP, Glance and IPCS. The following are our findings:
Oracle User Procs 1,350,700,000
Ora SGA 1,056,030,000
System 256,300,000
Buffer Cache 409,600,000 Dynamic DBC_MAX 10%
Free Memory 242,000,000
-------------------------------------------
Total 3,314,630,000
Phy Mem 4,294,967,296
-------------------------------------------
Difference 980,337,296

We have had a hard time understanding this difference between total physical memory and accountable memory, until it ocurred to us that we were using pseudo swap. A quick check in Glance of pseudo swap shows a size of 895 meg. Given some variance in the tools used and the time frame between runs this number approaches the total memory on the system.

Our defined swap space on the system is 4gig. Given that we only utilize about 50% of our swap space, do we need to run pseudo swap? Or, can we reduce the memory consumption of pseudo swap? We have plenty of available disk space, so would it be wise to increase the swap space and turn pseudo swap off?

[Sridhar Bhaskarla · Accepted solution]

Hi Jason,

Nothing is consumed out of memory for Pseudo swap. This is only helpful in getting the reserve space adjusted for the system so that you can bring up more processes than the configured swap.

If you have available disk space, you can disable swapmem_on parameter to disable pseudo swap to get your accounts correct.

-Sri

[A. Clay Stephenson]

Hi Jason:

Remember that psedoswap doesn't actually use any memory. It's really intended for systems that have a large amount of RAM (e.g. 32GB) and a small amount of swap (e.g. 512MB). It a way of telling the OS that yes I know that if I need to pageout there may be no place to put it but that's okay I'm never going to do that to you. It also rather difficult to add up add the memory used by processes because many processes use common shared library functions and processes running the same program (e.g. vi) share a common text segment but have individual data and bss segments.

Regards, Clay

[Jason Berendsen]

Thanks for the responses.
I figured as much but I thought I was on to some miraculous discovery of the unaccountable memory. So this means we can't account for almost a gig of memory. I know you can't account for all memory but isn't this a large amount?

[Sridhar Bhaskarla]

Jason,

For "accounts" yes.

-Sri