Subject: Re: how can kernel space expand to >1GB?
To: Jason Thorpe <>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: tech-kern
Date: 07/31/2003 16:13:37
In message <>,
Jason Thorpe writes:
>On Thursday, July 31, 2003, at 02:57  PM, Ming Lei wrote:
>> On linux, there is an option called HIGHMEM support that enable the 
>> kernel to access larger physical memory, more than 1GB on i386. The 
>> way they do it, if I understand correctly, is that use a region in 
>> kernel virtual space to dynamic mapping high physical memory.
>NetBSD doesn't require any special options to do this.  You can still 
>dynamically remap any part of RAM into the kernel virtual address 
>space.  This is nothing really special -- it's basic functionality of 
>the VM system.

When configuring Linux 2.2 (and 2.4?) i386 kernels, you have (had) a
config-time option to select for 1Gbyte[*] or 2Gbtyes of KVA.  The max
user VA space is then, 3 Gbytes or 2Gbytes, respectively.

I suspect that's what Ming Lei is getting at.