Contiguous Memory Allocation (CMA) command line

Hello,

On RHEL 7.4 we are trying to enable a large contiguous chunk of memory via the kernel command line cma=64M. We have a driver that will allocate the 64M chunk of memory using dma_alloc_coherent. The call fails with anything larger than 4MB. Our understanding is the cma=64M should allocate a large contiguous chunk of memory for a call like dma_alloc_coherent to use. Is there any way we can find if the cma=64M kernel parameter is working?