topic Re: memory usage in Operating System - HP-UX

memory usage

Adrian_72 — Wed, 17 Nov 2004 16:04:29 GMT

Could you give me information about the concept of active virtual and active real memory:
Memory Stat total used avail %used
physical 2560.0 2518.9 41.1 98%
active virtual 3195.4 569.3 2626.1 18%
active real 1773.5 328.6 1444.9 19%
memory swap 1579.7 1220.3 359.4 77%
device swap 2048.0 2048.0 0.0 100%

Re: memory usage

Sridhar Bhaskarla — Wed, 17 Nov 2004 16:21:48 GMT

Hi Adrian,

How did you get these numbers?. Different tools show the usages differently based on the collection mechanism and the collection intervals. If this is from top, then

The system has 2560MB of physical memory out of which 2519MB is used.

The total virtual memory allocated to (or requested by) the processes is 3195MB out of which 569 MB was active during the last interval.

Total real memory active has been 1774 MB. Around 329MB was used in the last interval. Real memory pages are really the memory pages that were being used.

1580MB of memory was alloted as 'swap' out of which 1220MB is 'not available' anymore for swap purposes.

2GB of area has been alloted as swap from the disks. You don't have anything left.

This clearly shows that you are running *over and above* out of memory. You will need to add more memory. One area to look for memory wastage is 'dbc_max_pct' kernel parameter. If it is still at 50%, which is it's default, reduce it to get around 500 MB. If you can't do anything, then add more memory. I would say add *atleast* another 2 GB as you have 2 GB sitting on the device swap already.

-Sri

Re: memory usage

Steven E. Protter — Wed, 17 Nov 2004 16:22:29 GMT

Memory in hpux speak

ram plus swap

8 gb ram 6 gb swap 14 Gb of memory.

Its okay to reserve part of that 6 GB of swap but if you start using it you slow down fast. Watch for paging.

Your ouptut appears to be from swapinfo -tam

IT shows you are using all ram, and nearly all swap. You need memory or less work for your machine.

Virtual memory is disk memory that is used like memory. In essence swap. Its not real memory in the form of a fast chip, its kind of fake or psuedo memory to enable the system to swap out processes and keep running when actual ram(physical) memory is short.

SEP

Re: memory usage

Sanjay_6 — Wed, 17 Nov 2004 17:14:55 GMT

Hi Adrian,

Try the memory management white paper,

http://www2.itrc.hp.com/service/cki/docDisplay.do?docLocale=en_US&docId=200000062686726

The itrc doc id is WP1030009A.

Hope this helps.

Regds

Re: memory usage

Con O'Kelly — Wed, 17 Nov 2004 17:47:34 GMT

Hi Adrian

Both Sri and SEP have explained the memory figures to you.

In terms of memory utilsation on systems I would pay partiular attention to the amount of free memory, page out rate and swap utilisation.

You can use glance (options 'm' & 'w')to get a breakdown of memory and swap utilisation.

If you don't have glance the following command will show you free memory in MB.
# vmstat 1 2 | egrep -v 'procs|free' | tail -1 | awk '{ print $5*4/1024 }'.

You can also use vmstat to view pageout (po) rate.

Another good utility is kmeminfo (usually in /usr/contrib/Q4/bin). This gives an excellent breakdown of memory usage. The figures are in 4k pages, so you need to multiply by 4 to get figures in Kb.

Have a look at this excellent HP paper on memory for more info.
ftp://eh:spear9@hprc.external.hp.com/memory.htm

Cheers
Con