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

From: Joerg Sonnenberger <joerg@xxxxxxxxxxxxxxxxx>
Date: Wed, 8 Jun 2005 20:20:22 +0200
Mail-followup-to: kernel@crater.dragonflybsd.org

On Wed, Jun 08, 2005 at 10:18:02AM -0700, Matthew Dillon wrote:
>     We don't have any PAE code in DragonFly.  I don't currently intend
>     to add it... it's a severe hack.i [snip]

Let me elaborate a bit more on this. PAE makes the kernel work a lot
harder, because the kernel can't access all memory at the same time.
This means that you have to be a lot more careful when accessing
memory, since it might currently not be present.

It also adds the general problem of 64bit machines in that many PCI
bus master devices still only support "low" memory (below 4GB). For
this reason you often don't gain anything from using it e.g. for
buffer caching, since you have to copy it into the low memory or
reverse before doing IO.


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