The CMA debugfs interface is useful to retrieve basic information out of the
  different CMA areas and to test allocation/release in each of the areas.
  
  Each CMA zone represents a directory under <debugfs>/cma/, indexed by the
  kernel's CMA index. So the first CMA zone would be:
  
  	<debugfs>/cma/cma-0
  
  The structure of the files created under that directory is as follows:
  
   - [RO] base_pfn: The base PFN (Page Frame Number) of the zone.
   - [RO] count: Amount of memory in the CMA area.
   - [RO] order_per_bit: Order of pages represented by one bit.
   - [RO] bitmap: The bitmap of page states in the zone.
   - [WO] alloc: Allocate N pages from that CMA area. For example:
  
  	echo 5 > <debugfs>/cma/cma-2/alloc
  
  would try to allocate 5 pages from the cma-2 area.
  
   - [WO] free: Free N pages from that CMA area, similar to the above.