On Thu, 3 Jan 2002, David Brownell wrote:
> Now I'm not following _you_ ... could you give an example of
> what you mean?
A driver on a 64bit system with a 32bit host controller, if the system
has more than 4GB of RAM.
> In my proposal, device drivers would be able to either use
> the current rules (which they do already, so no problem :)
> OR (new) specify highmem buffers by {page+offset, length}.
I am not convinced that the current rules will remain OK.
At present AFAIK GFP_KERNEL will allocate memory the PCI layer can deal
with. Now I might be wrong but "dealing with" could be quite expensive.
In fact on a 64bit system without an IO-MMU it might mean a physical copy.
Even with an IO-MMU there might be a default setting that's cheaper to
use.
So either we restrict the drivers in many cases needlessly to a subset
of memory or we waste performance.
Regards
Oliver
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