linux-kernel - A question about ZONE

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Message-ID: <20101013145240.GE12467@foucault.redhat.com>
Date:	Wed, 13 Oct 2010 10:52:41 -0400
From:	Casey Dahlin <cdahlin@...hat.com>
To:	linux-kernel@...r.kernel.org
Subject: A question about ZONE_DMA

Hi all,

So if I understand correctly, ZONE_DMA exists to separate and preserve the
chunk of memory to which older ISA cards are capable of doing DMA. The question
that arises for me is:

1) Why do /all/ 32-bit boxes have a ZONE_DMA when surely only a tiny and
shrinking number of them have a need for it?

2) Why do /any/ 64-bit boxes have a ZONE_DMA? Is there really some godless
monster out there who put an early ISA bridge and a 64-bit CPU on the same
motherboard?!

Can someone shed light on what I'm missing?

--CJD
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