topic Tuning the pseuo-swap space in Operating System - HP-UX

Tuning the pseuo-swap space

Radheya — Thu, 16 May 2002 16:15:34 GMT

I have HP-UX running on my UNIX box. The

swapinfo shows:
/usr/sbin/swapinfo -t
memory 674956 135700 539256 20% ==> Usage.

I would like to know how do I modify this pseuo-swap ??? What tunable needs to be used ??? Is it swapchunk/maxswapchunk???

Re: Tuning the pseuo-swap space

James R. Ferguson — Thu, 16 May 2002 16:27:03 GMT

Hi:

Pseudoswap is either on or off as controlled by 'swapmem_on'. Clearly, as indicated in the output of the "memory" line from 'swapinfo', you have pseudoswap enabled.

You would increase 'maxswapchunks' to allow device and filesystem swap to be enlarged. 'swchunk' translates into the I/O size in blocks written to a swap device and therefore comes into play when balancing I/O between multiple swap devices.

Regards!

...JRF...

Re: Tuning the pseuo-swap space

Mladen Despic — Thu, 16 May 2002 16:44:38 GMT

Pseudo-swap reservations are controlled by a counter swapmem_cnt. The counter starts at the value equal to 3/4 of the total physical memory and is decremented as more processes reserve pseudo-swap. The counter does not indicate that any additional memory of swap space is actually used, it's just a counter. The only problem occurs when the counter is reduced to 0. This is equivalent to 'swapinfo -t' showing 100% utilization for memory. I would only be concerned if the percentage is likely to hit 100%.

Re: Tuning the pseuo-swap space

Mladen Despic — Thu, 16 May 2002 16:48:42 GMT

For more information, see
/usr/share/doc/mem_mgt.txt
and look for:
"Reservation of Physical Swap Space"

Re: Tuning the pseuo-swap space

Anthony deRito — Thu, 16 May 2002 17:12:07 GMT

pseudoswap is extremely useful on systems with
large memory so that you don't need to match or double the amount of actual/physical swap that has been recommended. Pseudoswap's size is
calculated based on 75% of memory. This 75% is just a calculation. But this does not mean that memory is taken by pseudoswap. On the contrary, pseudoswap doesn't exist.

"The system will use pseudo swap only for reserving space and does not page processes in and out of pseudo swap. In the event that processes need to be paged out of physical memory, the kernel will swap to device or filesystem swap."

Pseudo swap is turned on by default and can be turned off by changing the kernel parameter swapmem_on to off.

Tony

Re: Tuning the pseuo-swap space

Sanjay_6 — Thu, 16 May 2002 17:15:27 GMT

Hi Radheya,

Try this link,

http://us-support.external.hp.com/cki/bin/doc.pl/sid=064e7a40015481c3ca/screen=ckiDisplayDocument?docId=200000048595137

Hope this helps.

Regds

Re: Tuning the pseuo-swap space

PIYUSH D. PATEL — Thu, 16 May 2002 17:16:20 GMT

Hi,

For tuning the pseudo-swap you need not change the maxswapchunks/swapchunk.

How much memory does your system has ??? Are you having any performance problems

Piyush