From owner-freebsd-hackers  Mon Mar 12  1:26:50 2001
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To: clash@tasam.com
Cc: bright@wintelcom.net, ianc@ednet.co.uk,
	freebsd-hackers@FreeBSD.ORG
Subject: Re: Greater than 2GB per process
In-Reply-To: <003701c0aaaf$a4566ce0$dc02010a@fireduck.com>
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Date: Mon, 12 Mar 2001 01:25:28 -0800
From: Jordan Hubbard <jkh@osd.bsdi.com>
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> I know very little about how kernel or low level processor stuff works, but
> shouldn't we be able to do a 4GB process on a 32-bit system?
> The limitation of 2GB per process should only be an issue if there is some
> need to use signed numbers, right?

Well, that single 4GB of address space is divided up into kernel data
structures, which are in the address space of the process but subject
to various levels of MMU-provided memory protection, and the process'
own "user data."  I believe the break is currently set in the middle
at 2GB, and various attempts to adjust it more aggressively (in user
data's favor) have been interesting but ultimately also proved to
break things like BSD/OS binaries, which have their own assumptions
about the setting of the break.

- Jordan

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