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Subject: Re: i686 SMP systems with more then 12 GB ram with 2.4.x kernel ?
To: znmeb@aracnet.com (M. Edward Borasky)
Date: Tue, 1 Jan 2002 18:46:40 +0000 (GMT)
Cc: alan@lxorguk.ukuu.org.uk (Alan Cox),
        harald.holzer@eunet.at (Harald Holzer), linux-kernel@vger.kernel.org
In-Reply-To: <HBEHIIBBKKNOBLMPKCBBMEAHEFAA.znmeb@aracnet.com> from "M. Edward Borasky" at Jan 01, 2002 10:15:59 AM
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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
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> 1. Shouldn't there be *four* zones: (DMA, low, high and PAE)?

Probably not. PAE isnt special. With PAE you pay the page table penalties
for all RAM.

> 2. Isn't the boundary at 2^30 really irrelevant and the three "correct"
> zones are (0 - 2^24-1), (2^24 - 2^32-1) and (2^32 - 2^36-1)?

Nope. The limit for directly mapped memory is 2^30.

> 3. On a system without ISA DMA devices, can DMA and low be merged into a
> single zone?

Rarely. PCI vendors are not exactly angels when it comes to implementing all
32bits of a DMA transfer


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