topic Re: swap(paging) happened in Operating System - HP-UX

swap(paging) happened

Gary Yu — Wed, 05 Jun 2002 18:13:48 GMT

Hi all,

swapinfo shows that there're 4% swap area been used(in the"dev" line) on one of my HPUX box, which means paging happened on this box. My concern is, is it the case that we were running of physical RAM when paging happened, I mean, is it possible that RAM still avaible but the OS tried to page out some process?

the other question is, is it a serious problem when paging happened, the other guy here said the companies he worked for always had at least 20% swap used.

thanks a lot

Re: swap(paging) happened

Martin Johnson — Wed, 05 Jun 2002 18:25:23 GMT

The amountof swap space in use is not a problem. How much swap space is used depends on the number and size of the programs you are running.

What is a performance concern is swaping - the copying of pages to/from memory from/to disk.

to determine the amount of swaping, use vmstat or glance.

Marty

Re: swap(paging) happened

Gary Yu — Wed, 05 Jun 2002 18:40:46 GMT

thanks Martin for the reply, actually I'm not concerning about the disk space. But I do concern about the performance. what I want to know is that, generally, is it normal to have swap area been used, and how may percentage usage is acceptable(before we decide to extend the RAM)?

thanks,

Re: swap(paging) happened

Martin Johnson — Wed, 05 Jun 2002 18:54:14 GMT

On some of my systems, swap sapce is up to 90% utilized. I have MeasureWare alert me when swap space is more than 95% full. At that point I usually add a second (or third) swap file.

If you are using only 4%, you are probably wasting disk space, but that is not hurting anything.

Marty

Re: swap(paging) happened

PIYUSH D. PATEL — Wed, 05 Jun 2002 18:57:40 GMT

Hi,

I have observed that during the peak hours the swapping goes to more than 50% also. But it is momentarily. If the swapping is happening regularly and that too above 30-40% then you be concerened. Or else there is no problem.

Can you give us the ouput of the swapinfo -t command and how much is your swap space and memory.

Piyush

Re: swap(paging) happened

S.K. Chan — Wed, 05 Jun 2002 19:02:49 GMT

"..is it possible that RAM still avaible but the OS tried to page out some process?"
Yes, due to memory map files. Look at this thread, it was just today ..

http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x0f2b8f960573d611abdb0090277a778c,00.html

hope it helps ..

Re: swap(paging) happened

Bill Hassell — Wed, 05 Jun 2002 23:11:33 GMT

There is oe other reason that swap space is used: memory mapped files. Even though you never come close to using the amount of RAM you have, memory mapped will occupy a small portion of swap space. Nothing to worry about. If you want to see actual paging rates, run vmstat and look at PO (page out). You'll probably see mostly zeros.