Memory Allocation in RedHat Linux

[Jorge Cocomess]

Hi,

My server has a total of 8GB of physical Memory. I know that Linux kernel pre-allocate as much memory as possible. If I only want the Linux kernel pre-allocate or allocate just 4GB instead of 7+ GB of Memory, how would I do that? If that's the case, would you advise doing so or is this best practices?

Thank you in advance,

Jorge

[Jorge Cocomess]

Sorry, I forgot to mention that I'm running RHAS 4.0 - 8GB Memory w/12GB Swap space.

Thanks,
J

[Frank_W]

Hi Jorge,

the linux kernel is using the part of the memory, that is not used for processes, as disk-cache to get a better I/O performance.

You can see the memory usage with the command "free".

If you start some new processes, the kernel will immediately release some of the cache-memory, so you have no disadvantage.

[Court Campbell]

If this is a 32 bit version of rhel then the kernel sits in the first GiB of memory and is only approx 879MiB.

[Jorge Cocomess]

This is a 64-bit version of RedHat.

Where else should I be looking at for performance tuning?

Thanks,

Jorge

[Court Campbell · Accepted solution]

It really depends on what is going on with your system. You need to find out what is being 100% utilized. For memory you can see if you are starting to swap. If so, you could add more memory and/or try adjusting the amount of memory that certain apps use. But I am not sure where your bottlenecks are, or if you even have any. You can use "sar -r" and vmstat to see if you are swapping. You can use "iostat -x" to see disk utilization. You can use "sar -u" to see cpu usage. You could also look at installing collectl. I have been using it for a while and find it pretty useful.

It is really truly hard to tune a system without any measurements.

[Court Campbell]

I have been reading up on zone_normal on x86_64 and it isn't a tunable parameter. Later.

[Jorge Cocomess]

Hi Court,

Where could I find the utility 'Collectl" that you've mentioned?

Thanks so much for your input.

Jorge

[Asif Sharif]

Hi Jorge,

Collectl is a light-weight performance monitoring tool capable of reporting interactively as well as logging to disk. It reports statistics on cpu, disk, infiniband, lustre, memory, network, nfs, process, quadrics, slabs and more in easy to read format.

Download collectl from below link.

http://sourceforge.net/projects/collectl/

See the doc on the following link.

http://docs.hp.com/en/5991-7402/ch07s07.html

Regards,
Asif Sharif