Subject: Re: how can kernel space expand to >1GB?
To: Ming Lei <mlei@Brocade.COM>
From: Stephan Uphoff <>
List: tech-kern
Date: 07/31/2003 20:08:21
Ming Lei wrote:
> netbsd does have an config option to split kernel/user space to 1G/3G as
> linux does. This option exists for every platform.
> Jason, sorry that I didnt make myself clear in the previous emails. Let's
> get an example, say I have kernel subsystem D(D is not an user app!) needs
> to use *lots of memory* and I enable the code to use all the kernel memory
> that I can grab. Do you think D has the limit of how much memory it can use?
> I think D would first reach the limit posted by kernel 1GB virtual memory
> restriction. When all the kernel virtual addess(1GB) are exhausted, and if D
> wants even more memory(see there are still some phys memory left), how does
> kernel do?
> This is basically my question.
> Thanks,
> Ming

NetBSD does not linearly map physical space into the kernel virtual space.
You can however allocate purely virtual kernel space and use it to map/unmap
arbitrary physical pages later.
Think of it as always using HIGHMEM.