Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m

Jes Sorensen
2001-07-11T19:18:06Z

>>>>> "David" == David S Miller <davem@redhat.com> writes:

David> Alan Cox writes:
>> I see no good way to optimise for 64bit dma on a 32bit box.

David> I'm actually not only talking about DAC device on 32-bit cpus.
David> Just as much, I'm talking about drivers for SAC-only devices
David> even on 64-bit cpus.

David> I took a lot of crap from driver authors when we started
David> pushing the PCI dma stuff on people, because of the dma_addr_t
David> people now had to keep around to unmap the thing later.

David> To a certain extent I agreed with these folks. I'll be gutting
David> myself if I make everyone eat twice as much space just to add
David> DAC support to the kernel :-)

The overhead is going be negligeble, the overhead of highmem itself is
much worse. Not to mention that today some dma_addr_t's might not be
packed properly in data structure hence they ending up taking 8 bytes
anyway.

Jes