Re: Kernel memory limits?

[linux-os]

On Thu, 17 Mar 2005, Peter W. Morreale wrote:

> (I did not see this addressed in the FAQs...)
>
> How much physical memory can the 2.4.26 kernel address in kernel context on 
> x86?

All of it.

> What about DMA memory?

All of it, too. The old DMA controller(s) could only address 16 MB
because that's all the page-registers allowed. Bus-mastering DMA
off the PCI/Bus has no such limitation. Most have DMA controllers
that use scatter-lists so RAM doesn't even have to be contiguous,
only properly allocated (in pages) and nailed down with no caching.

> Local rumor says ~1GB.  But this makes little sense given a 32-bit address.

If you are looking for a dynamic buffer in DMA-able RAM, you probably
can only use aout 1GB, but that's not how to do DMA.

> Where in the source can I learn more about this?

../linux-`uname -r`/mm

> Thanks,
> -PWM

Cheers,
Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
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