cvs commit: src/sys/dev/bce if_bcereg.h

Scott Long scottl at
Wed Apr 26 05:46:57 UTC 2006

Matthew Jacob wrote:
>> Supporting sizes >= 4G sounds unreasonable.  How can a single device
>> need or even address so much space, even on 64-bit arches?  For vm,
>> virtual memory is sort of a device, but even it is limited to 4G on
>> 32-bit arches, and PAE on i386 isn't pessimized by using a larger than
>> necessary vm_size_t.
> I have need to support and help people sell machines that use 32GB of 
> directly addressable memory. In fact, the EM64T cheat will shortly 
> become an embarrasment to Intel when people find out that EM64T with PAE 
> is *not* the same as Opteron (36 vs. 40).
> I'm afraid I don't understand the 'unreasonable' argument here. Linux is 
> eating your lunch today. Do you want it to eat your dessert as well?
> -matt

bus_size_t is used for things like measuring transfer segment size. 
There is little chance that Linux, Windows, FreeBSD, or any other OS
is ever going to try to DMA more than 2^32 bytes of data in a single
bus transaction.  Maybe you could contrive a silly infiniband device
to do it.  Anyways, it has no bearing on whether the CPU, memory
controller, or PCI buses can do 64 bit addressing.


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