Subject: Re: 4MB pages?
To: Ignatios Souvatzis <>
From: Jason R Thorpe <>
List: tech-kern
Date: 09/06/2000 23:11:48
On Thu, Sep 07, 2000 at 06:56:39AM +0200, Ignatios Souvatzis wrote:

 > PowerPC using BATs, size is 2^n bytes, where n is 17...28.
 > However, those are a limited resource; only 4 sets for
 > data and 4 for instructions are implemented in hardware.
 > The pmap currently only uses them to map most of (kernel) accesses 1:1.

Actually, the PowerPC port's use of BATs is quite clever.  There is a
pool of free BATs that are used to essentially map the entire physical
address space 1:1 using a `spill' handler .. i.e. like a different TLB
miss handler that treats the BATs like a really big TLB.

Took me a while to figure that out :-)

        -- Jason R. Thorpe <>