Re: Kernel Compilation for Dual Xeon system

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

Rob, thanks again.

Here's what the Kernel help system says on selecting "User address space
size":

	Typically there will 128 megabytes less "user memory" mapped    
	than the number in the configuration option. Saying that        
	another way, "high memory" will usually start 128 megabytes     
	lower than the configuration option.                            

	Selecting "05GB" results in a "3.5GB/0.5GB" kernel/user split:  
	On a system with 1 gigabyte of physical memory, you may get 384 
	megabytes of "user memory" and 640 megabytes of "high memory"   
	with this selection.

Why would I want that?  
What is the advantage of having a high ratio of "high memory"?
What is this "high memory" used for, the kernel and drivers?
How do I gauge how much high memory I need?

	Selecting "1GB" results in a "3GB/1GB" kernel/user split:       
	On a system with 1 gigabyte of memory, you may get 896 MB of    
	"user memory" and 128 megabytes of "high memory" with this
	selection. This is the usual setting.                     

And on a 2GB system would I get 1152 MB high and 896MB user?

	Selecting "2GB" results in a "2GB/2GB" kernel/user split:       
	On a system with less than 1.75 gigabytes of physical memory,   
	this option will make it so no memory is mapped as "high".

Does that mean I get 128/1920 with 2GB of physical RAM?
And 0/1024 with 1GB of physical RAM?
And what are the cons of having no high memory?

To summarize, how much does all this affect performance and in what way?

--
  Simon Oliver