Re: Kernel Compilation for Dual Xeon system

[Simon Oliver <simon.oliver@umist.ac.uk>]

Rob, 

thanks for the quick response

"E. Robert Bogusta" wrote:
> 
> > - what to set for User address space size - why?
> 
> Unless you really need big user space, go small. An issue of table space
> again, although it isn't a big one.
What is big user space?  I have one application that will use about 1GB
RAM, another (on another server) uses between 40MB and 500MB.

What is are the pros and cons of setting a large/small user space.

For example if I have a 1GB user space defined but a process needs to
address 1.5GB?  

Or conversly if I have configured for 1GB user space but never use more
than about 250MB user space.

Finally.  What will have happen if I compile the kernel with support for
4GB RAM (even though I only have 2GB) then set the user space to 2/2GB?

> You may want to try that and draw your own conclusion. It depends a lot on
> how many processes you run and how active their data set might be. I would
> assume that the vendor is right, but I would be curious enough to check
> just in case.
This is a memory mapped daemon application - it loads an entire database
(~1GB) into RAM and waits for jobs.

> I'd try a
> kernel compile with -jN, with N=number of processors, physical or logical.
> You might run a tad faster adding 1 to that N, making it larger than that
> is usually worse.
I've seen this advice in the smp readme with the kernel source.  I thought
that this only affected kernel compilation speed - I didn't realise it
affected overall system performance - how does it do that?

Finally, and good resources on this - I had a look around but couldn't
find much up-to-date stuff about?

Thanks again

--
  Simon Oliver