HP-UX11 Phisical memory not fully used

[Roberto Pavani]

On a J5600 Machine with 2GB of RAM a process of 2014Meg is using approx 1GB of RAM. The Cpu time dedicated to the process is very low (2%) and vhand is running. On another machine with 4GB of RAM (J5600) the same process is running fine using 1.9GB of Phisical RAM and using 99% of CPU time. Both machines are using HP-UX11. Are there some kernel paramenter to let a process to use more than HALF Physical memory ?
Could be possible that the system is using half phisical memory for each of the two processor?

Regards

Roberto Pavani

[linuxfan]

Hi Roberto,


Check out the kernel parameter
swapmem_on
kmtune -l -q swapmem_on

swapmem_on enables or disables the reservation of pseudo-swap, which is space in system memory considered as available virtual memory space in addition to device swap space on disk. By default, pseudo-swap is enabled(1)

Also check dbc_max_pct
(kmtune -l -q dbc_max_pct_

For more information about the kernel parameters, check out the link
http://docs.hp.com/hpux/onlinedocs/os/11i/kcparams/KCparams.OverviewAll.html

-Regards
Ramesh

[Praveen Bezawada]

Hi
I am not sure if there is a single configurable parameter to make an application use only half of the ram.
I think what's happening is due to setting of different parameters. I suggest that you compare the kernel setting of the two machines to check where the big difference lies. The kernel parameters to check are
1) nfiles
2) nkthread
3) maxthread_proc
4) maxfiles and maxfiles_lim
5) maxdsiz
6) dbc_max_pct
7) semmni
8) nproc
9) shmmax

All the best....
...BPK...

[Sridhar Bhaskarla]

You need to check the kernel parameters related to Shared Memory segment in particular shmmax.

Unless you are using Process Resource Management (PRM), it's not possible to adjust the system usage per process basis.

You also need to be little bit more specific on how your process works. Are there any inputs to the process?. Process resource utilization varies depending on it's load.

-Sri

[Wodisch]

Hello Roberto,

if your system is only using up that few cpu-cycles, it
seems to just not need all that RAM...
Does your application really do the same calculation
as on the other machine?
The other point would be to check your swap space:
swapinfo -t
Doe you have another GB of swap space free?
Or do you have a line starting with "memory" in the
output of that command?
Having not enough virtual memory (read: swap space)
would actually make it impossible to use more RAM...

HTH,
Wodisch

[Patrick Wallek]

OK. On the machine with 2GB of RAM and a process size of 2014MB, with the process only getting 2% CPU and you say vhand is running, I would bet that you are pageing like crazy!!! You are paging so much that nothing else is getting accomplished. There is nothing that explicitly says that a process can only use 1/2 of system memory. Your problem is that the other 1GB of your RAM is in use by something else. Some likely culprits are normal system process, other applications that may be running and Buffer Cache. If you kernel parameter dbc_max_pct is set to its default value then 1/2 of whatever memory you have can be taken over by your Dynamic Buffer Cache. I would recommend setting this down to 15 or 20 percent so that you will only have 300 - 400 MB being used by buffer cache instead of 1 GB. This will give you another 600-700 MB of RAM available.

The problem is, if this process used 1.9 GB of memory on your 4GB system then trying to run the same thing on a 2 GB machine is asking for trouble. You will NEVER have then entire amount of memory that you have installed on a system available because normal system processes, buffer cache, etc. will use some amount.

Setting your buffer cache down on the 2GB machine will help, but your best bet would be to install another 2GB or so of RAM to really get the performance you require.