Size in Mega Bytes

configname: CONFIG_CMA_SIZE_MBYTES

Linux Kernel Configuration
└─>Library routines
└─>Size in Mega Bytes
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Defines the size (in MiB) of the default memory area for Contiguous
Memory Allocator. If the size of 0 is selected, CMA is disabled by
default, but it can be enabled by passing cma=size[MG] to the kernel.