allocating large piece of contiguous kernel memory

[Hartmut Brandt]

Hi all,

for a device driver communicating with an FPGA I would like to allocate
an 8GByte piece or two 4GByte pieces of contiguous memory in the device 
driver. The machine is amd64 and has 256GByte.

The maximum I can allocate is 512MByte. If I try more (in one piece or in 
two pieces) contigfree() crashes in pmap_resident_count_dec() with an 
"pmap resident count underflow".

Is this something which is not supposed to work? Or is there something 
tunable or is this a bug?

Regards,
harti