swap(paging) happened

[Gary Yu]

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

[Martin Johnson]

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

[Gary Yu]

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,

[Martin Johnson]

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

[PIYUSH D. PATEL]

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

[S.K. Chan]

"..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 ..

[Bill Hassell]

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.