Process locked on VM

[Olivier Masse]

Help! I have a performance problem with an application our developpers have ported to HP-UX from OpenVMS. They're stress testing it and it performs slowly. Some people are getting nervous. It won't be long before they start claiming it's OS-related.

Here is the problem: Even if there is plenty of free memory left (6Gb), there is tremendous activity on the disk where the app is installed (100%) and glance report all that activity as VM. I don't understand how there could be VM activity on that disk since no swap space is on it.

The system it not paging at all, only page ins are reported by glance and vmstat, no pageouts. Many of processes are reported by glance as being blocked on VM.

I'm mystified by this.

I'm pretty sure there's a problem somewhere in the code, probably a spinlock (the app relies a lot on share memory -- but how could that be reported as VM?). But I'm not a developer so I can't tell for sure. I need to give the developers some meat. I'll also strongly suggest Caliper runs tomorrow but I'm looking for the most arguments I can get.

I've opened a software call about this but I have to go through 1st level first and this could take a while, maybe some people here have an idea on what's going on?

Thanks, points will be awarded.

[Dennis Handly]

If there is a lot of I/O activity on the APP disk, is it loading and unloading shared libs? This may show up as page ins.

Or is the application doing lots of forks? (But this would not be to/from the APP disk.)

I assume you aren't starting lots of small processes?

>probably a spinlock

This won't do I/O.

>I'll also strongly suggest Caliper

Yes, that would help. You could also try tusc to see what system calls are being done.

[Steve Lewis]

Hi Olivier,

Please post the output of swapinfo -tm, vmstat, ipcs -msqa.
Pageins aren't as bad as pageouts, but >0 is still worse than 0.
If it uses shared memory, have the developers used shmctl with SHM_LOCK to lock it in memory?
Have you tuned the kernel, if so, how?

[Olivier Masse]

Thanks for the replies

Problem seems to be a bug in the application. I don't have a clue why it's reported as VM activity. I'm waiting for the developpers to profile their app with Caliper.