Paging Activities

[Ricky_2]

Hi, I see from swapinfo that my mem swap is 33% used and my 2 equal priority device swap are each 14% used. From vmstat, I also see approx. 1500 free pages. I assume that meant I have more than sufficient mem, right? Why is it then that there are still paging activites under pi and po from vmstat? Can someone point me to good documentations on performance monitoring and tuning? Thanks in advance.

[S.K. Chan · Accepted solution]

A very common misconception. You're seeing the paging activities (under no memory constraint) simply because the applications that are running on your system are utilizing the memory-mapped files (created from system calls) which does not use the filesystem buffer hence reading/writing directly from disk to memory and vice-versa. That in effect is like paging. Now for the doc .. check out this whitepaper by Stephen Ciullo .. good read.
http://www.docs.hp.com/cgi-bin/otsearch/getfile?id=/hpux/onlinedocs/os/11.0/tuningwp.html&searchterms=stephen&queryid=20021002-212206

[Animesh Chakraborty]

Hi,
The attached document may be helpfull.

[Ricky_2]

Hi SK & Animesh, thanks for the prompt responses. I'll need some time to go through those docs. So SK, is it right to say that, depending on the apps running, it is usual to see a certain degree of paging with no direct relations to the sufficiency of memory?

[S.K. Chan]

Yes, Ricky. The system-calls that creates those memory-mapped files are not like the ordinary read/write functions to the filesystems that uses buffer cache, they in fact do paging straight to the disk purely to increase performance.