Re: i686 SMP systems with more then 12 GB ram with 2.4.x kernel ?

From: Alan Cox (
Date: Tue Jan 01 2002 - 13:46:40 EST

> 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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