Problem with 8G dma memory allocation

Problem with 8G dma memory allocation

[am jom]

I have a Supermicro x10drs-2u board, Intel Xeon E5, 2600v3, with PLX
NTB switch. I have installed Centos 7 and mainline linux kernel 6.5.3
with added PLX driver from TrueNAS. There 2 main boards with PLX ntb
devices already attached in hardware through a bus named M2

CMA and DMA are active and I can reserve like 8G, CMA memory at 4G.
There are other network devices using CMA and they are working. I know
that ntb_hw_plx.ko by Truenas needs 8G memory space

When i load ntb_transport.ko module, the related kernel thread crashes
by the following error message:

Unable to alloc MW buff of size 8,589,934,592

The problem is with dma_alloc_coherent() which fails and has errors
and it seems that it can not find any CMA reserved memory as the crash
dump reports (by dmesg) invalid operation in _alloc_pages() at last
and the "cma" term is not seen in the crash dump .

for CMA alignment i chose 2, and 2 areas and 8G size. what size and
alignment should i set by the kernel config variables?

Is there any kernel i can use to drive PLX ntb bridge device? Kernel
detects several PLX devices regarding this switch like PEX8717,
PEX8732 and 87d0 and ntb_hw_plx.ko is being attached to 8732 network
device