topic Re: Kernel parameter question in Operating System - HP-UX

Kernel parameter question

Antonio Dinis — Wed, 04 Aug 2004 08:59:44 GMT

Hi
after a panic in a HP9000 N class, HP send to me a mail with the analizys.
They recomend decrese

set dbc_max_pct to 6
set dbc_min_pct to 4

Hi have 10 and 5.
Wath do you think

Attached I sent all analizys.

Re: Kernel parameter question

Steve Steel — Wed, 04 Aug 2004 09:13:47 GMT

Hi

If it helps depends on how much memory you have but you seem to run out of swap

This could indicate a memory leak or not enough swap

Check these things
Memory Usage - â What is using all of the memoryâ ?

by:eric.herberholz@hp.com

Last modified: July 26, 2004

Latest version available at external ftp site:

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

espacially review buffer cache size

Also make sure your patch level is recent

Steve St

Re: Kernel parameter question

Franky_1 — Wed, 04 Aug 2004 09:18:07 GMT

Hi,

it depends on the memory you have, but decreasing the default values is alwasy a good thing, because otherwise too much memory is occupied.
So i have 4 GB Memory and set the values to 8 (max.) and 5 (min.) percent.
So i think the advice will be a good thing

Franky

Re: Kernel parameter question

A. Clay Stephenson — Wed, 04 Aug 2004 09:20:41 GMT

It looks like your machine died because it appeared to be drastically low on memory. Anything you can do to free up more memory will help. The changes to dbc_max_pct and dbc_min_pct are very small so they are not going to help or hurt very much.

Because the machine had been up a while, I suspect the real problem is that you have applications that leak memory. I would immediately start looking for those. The kernel patch is probably a good idea as well.

As a sysadmin, part of your job is to have monitors in place so that you know the box is under memory pressure long before serious problems arise.

Re: Kernel parameter question

Dietmar Konermann — Wed, 04 Aug 2004 10:40:19 GMT

Looking at your attachement I see a competent analysis of your problem. (Not a panic, BTW. User initiated TOC after system hang/thrashing). The recommendations at the end are valid... IMHO the dbc settings are not the most important ones.

Take care to get the recommended patches installed and check if the system is really suitable for your workload. The "working set" of your applications needs to fit into physical memory to avoid severe memory pressure like in your case. Period.

BTW, I don't beleive that your applications are "leaking" memory. Funny, but application memory leaks usually don't cause memory pressure on virtual memory systems. Leaked memory is usually no longer accesses, so it can be easily paged out after some time. So you would see an exhausted swap space instead.

Best regards...
Dietmar.

Re: Kernel parameter question

Ted Buis — Thu, 05 Aug 2004 14:48:00 GMT

The quick look I gave it indicated that you were out of swap space. I would try to increase that and see if you get page outs. If you do, then likely you will have to get more memory. How much device swap do you have?