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Subject: Re: Does ZONE_HIGHMEM exist on machines with 1G memeory
From: Robert Love <rml@novell.com>
To: Ronghua Zhang <rz5b@cs.virginia.edu>
Cc: linux-kernel@vger.kernel.org
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Date: Wed, 22 Sep 2004 00:55:10 -0400
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On Wed, 2004-09-22 at 00:39 -0400, Ronghua Zhang wrote:

> But why cannot we simply map the whole physical memory into the 1GB
> kernel virtual address space? In this case, we don't need to reserve any
> address space for the permanent or temporary mapping. Am I missing
> something here? Thanks

It is because of how the mappings work and where PAGE_OFFSET is.

With some hacking you can definitely use all 1GB without HIGHMEM, but
you would not be able to use more than 1GB.  And it would break ABI, at
least for modules.

	Robert Love