kernel 開啟cma

或者修改.config
CONFIG_CMA=y
CONFIG_CMA_AREAS=2
CONFIG_CMA_SIZE_MBYTES=8
CONFIG_CMA_SIZE_SEL_MBYTES=y
CONFIG_CMA_ALIGNMENT=11

The alignment is page order size, 4096 * 2^N. So an 8M alignment would be 4096 * 2^11.