pseudo swap

[The Witchking]

I have a rp7410, 12GB RAM, running Oracle and SAP/R3, HP-UX 11.11.

I notice that system memory utilization varies between 50-55%, with the remainder being user (and a little for buffer).

If I disable pseudo swap will I likely release any of the memory currently used by the system for user processes?

I have two device swap areas, each 20GB in size (yes - HUGE, set up before my time). Memory report in glance states:

Total VM: 15.7GB
Active VM: 4.04GB
Phys Mem: 11.8GB
Sys Mem: 6.43GB
Buf Cache: 630MB
User Mem: 4.63GB
Free Mem: 133.9MB

When sorting by VM and resident memory all the user processes have the lion's share (if not all) so I don't understand why the system is taking all this memory.

The reason I think memory is not what it should be on this box is that similar machines (Oracle, SAP/R3, rp7410, same RAM) only show a system memory usage of ~15%, with the rest being taken by user and a bit for buffer again.

Essentially the application and DBA teams want me to give them some of my system memory - I can't see where it's all being used and hence thought pseudo swap might have something to do with it.

Any help/tips would be greatly appreciated. Thanks.

[Steven E. Protter]

Shalom

Take a look at
swapinfo -tam
vmstat, look for paging.

Assuming you aren't actually paging in a heavy way, releasing psuedo swap should achieve what you wish.

SEP

[shridhar_1]

hi

if swapinfo -tam
shows a line

memory ...........

u r using pseudo swap

pseudo swap is actually 75% of ur total
ram

as per oracle is concerned
min 20 gb swap is required


HTH

shri

[Jerry P Antony_1]

Hi
You can take a better decision based on swapinfo command output.Disabling the pseudo swap will definitely give more free memory but that can affect the performance of your system.

Jerry

[The Witchking]

Hi All
Thanks for the replies, my swapinfo output:

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 24576 1452 23124 6% 0 - 1 /dev/vg00/lvol2
dev 20480 7269 13211 35% 0 - 0 /dev/vg00/lvswap
reserve - 6340 -6340
memory 9315 6148 3167 66%
total 54371 21209 33162 39% - 0 -

Not a huge amount of paging as you can see. Based on this, is it OK for me to go head and disable pseudo swap?

[Patrick Wallek]

This machine has 12GB has about 44GB of swap space.

I would say that yes, it would be safe to turn 'swapmem_on' off.

[A. Clay Stephenson · Accepted solution]

In the case of a machine that has SWAP (disk) >= RAM then pseudoswap serves no purpose. It is only a kernel bookkeeping trick for machines that have much less swap than RAM --- a not uncommon configuration these days. Pseudoswap doesn't swap; it doesn't use memory (or disk); it's just a way of telling the kernel that yes, I know what I'm doing and I know I have more memory than swap BUT I'm never going to swap --- that's why I bought all that memory in the first place.

[Arunvijai_4]

Hello,

From your memory params: I feel, if you disable "pseudo swap", you can gain some performance improvements.

-Arun

[Theodore Pardike]

I just upgraded to some rx4640's, and I always turn off pseudo swap in our
environment...increases lockable memory (which Sybase likes):

Stats from our last upgrade:

With pseudo swap enabled:
Memory Information:
physical page size = 4096 bytes, logical page size = 4096 bytes
Physical: 16765016 Kbytes, lockable: 12613956 Kbytes, available: 14636944 Kbytes


With pseudo swap disabled:
Memory Information:
physical page size = 4096 bytes, logical page size = 4096 bytes
Physical: 16765016 Kbytes, lockable: 14315312 Kbytes, available: 14636944 Kbytes

Ted