topic Re: Shared memory segment that has size greater than size of phisycal memory of the machine in Operating System - HP-UX

Shared memory segment that has size greater than size of phisycal memory of the machine

Alex Vinokur — Wed, 03 Nov 2010 07:51:50 GMT

Hi,

HP-UX ia64 v2
HP-UX ia64 v3

int shmget(key_t key, size_t size, int shmflg);

Is it possible to create shared memory segment that has size greater than size of phisycal memory of the machine?

P.S. How to know size of phisycal memory of the machine?

Thanks

Re: Shared memory segment that has size greater than size of phisycal memory of the machine

Turgay Cavdar — Wed, 03 Nov 2010 08:11:52 GMT

Hi,
The maximum size of the shared memory segment is controlled by the kernel parameter: shmmax. I think it is possible to create shared memory segment that the size is bigger then physical memory (this should be related to total virtual memory). You can see the physical RAM size with the command:
# machinfo

Regards.

Re: Shared memory segment that has size greater than size of phisycal memory of the machine

Dennis Handly — Wed, 03 Nov 2010 09:44:17 GMT

>Is it possible to create shared memory segment that has size greater than size of physical memory of the machine?

Sure, that's why they call it virtual memory.
If very much bigger, you'll do lots of swapping.

Re: Shared memory segment that has size greater than size of phisycal memory of the machine

Alex Vinokur — Wed, 03 Nov 2010 11:10:42 GMT

Dennis & Turgay, a lot of thanks.

Re: Shared memory segment that has size greater than size of phisycal memory of the machine

James R. Ferguson — Wed, 03 Nov 2010 11:26:03 GMT

Hi:

Yes, but you would be better advised to add more memory if your requirements are as you state.

You can ascertain the physical machine memory with:

# machinfo

...or for 11iv2, examine:

# dmesg

...or:

# echo "selclass qualifier memory;info;wait;infolog"|cstm > /tmp/meminfo

Regards!

....JRF...

Re: Shared memory segment that has size greater than size of phisycal memory of the machine

Alex Vinokur — Wed, 03 Nov 2010 13:22:20 GMT

James, thank you.