Curious high_memory difference between platforms

[David C. Chiu]

We are currently developing a module to service DMA-able buffer for our
PPC 405GP custom board and are using Monta Vista's 2.4.2 Kernel. We are
"rolling" our own allocation by using mem=xyz boot arguments followed by
a module implementing scheme similar to allocator module by Rubini
(Linux Device Drivers, O'Reilly.)

As with the allocator module, our module ioremap() the high_memory
pointer and does a write-verify to determine if valid memory exists.
Under x86 the high_memory reflects the memory size specified by mem=xyz,
but under PPC high_memory always reflect the total physical memory
installed. Is this normal?

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