vmstat

[rob nolen]

I'm trying to figure out something on my system.

I have some vmstat output that has 0 pages in, and 0 pages out. However, my reserved swap memory increases until it hits shmmax, and then I have some processes that start having problems.

I would think that if the process was having difficulty obtaining memory, it would be paging like crazy as it increased the reserved swap. However, according to this output, there are no paging operations taking place. My swap utilization is next to nothing as well.

Am I reading this correctly?

Vmstat/swapinfo output is attached.

Thank you in advance.

[Hein van den Heuvel]

Well, you have plenty of 'free' memory it seems, so there woudl be no need to actually swap out. A reserve will do just that: reserve swap space in case it is ever needed.

I suspect that when you write 'until it hits shmmax' this this is possibly just a coincident, the numeric values being the same.
Or... the process is indeed growing and touching shm, reserving swap space as it goes (grows!). When shmmax is hit, it can not grow further and it starts to misbehave, whilest your reserve swapspace would equal approx shmmax.
The problem would then be shmmax related, not swap related.

fwiw,
Hein.

[rob nolen]

Thanks for the reply.

The free memory column in vmstat, does that refer to free physical + virtual memory, or just free virtual memory?

As to shmmax, we've increased it to 6 GB, so if a process tries to grow past that, you're saying it could have problems? Why would it be trying to grow the memory allocation if it's not using it?

Thanks again for help.

[Jaime Bolanos Rojas.]

Rob,

This is a very well written document, very simple to read about memory.

It will give you all the answers that you are looking for

ftp://eh:spear9@hprc.external.hp.com/memory.htm

Regards,

Jaime.