DragonFly BSD
DragonFly kernel List (threaded) for 2005-06
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Re: PAE with dragonfly

From: David Rhodus <sdrhodus@xxxxxxxxx>
Date: Wed, 8 Jun 2005 19:01:54 +0000

On 6/8/05, Craig Dooley <xlnxminusx@xxxxxxxxx> wrote:
> Doesn't AMD64 use PAE for large address spaces?  I thought the Page
> Table structures were the same for both.
> -Craig

No, on AMD64 when operating in long mode the address space is 64bit. 
PAE is a 32bit hack that lets you access a few more bits.  34, 37 ?  I
don't recall exactly off the top of my head.

There are some interesting uses for PAE on the regular ia32
architecture such as allowing the kernel a full 4Gig memory and the
userland a full 4Gig of memory.  This actually makes the kernels life
a lot easier, though almost no one has this type of setup so its
mostly a moot development point.  About a year ago I had a working
implementation of PAE working on DragonFly, though I only had one test
machine with 4.5 Gigs of memory.  I also only had access to the
machine for a few days so I never had time to go through and optimize
the code.

I can look around for the old patch if someone has access to some
machines with more than 4 gigs of memory and someone that also has
time to revive it.


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