Re: High Mem Options

William Lee Irwin III (
Wed, 5 Mar 2003 04:57:47 -0800

On Wed, Mar 05, 2003 at 01:49:37PM +0100, Michael Vergoz wrote:
> That i can't understand i when the system going to the protect mode.
> How the system can use over 4GB memory ?
> On freebsd, when you have over 4GB the system say "XGB of XGB skiped..."
> (i'v got a machine with 8GB running on freebsd and without memory spare)

The cpu can't look at more than 4GB at a time.

Protected mode doesn't help this, turning paging on and PAE on does.

What it can do is point pagetables at different 4GB subsets of memory.

c.f. kmap_atomic() for how to window around using what's actually a
very small set of PTE's.

-- wli
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