The CMA debugfs interface is useful to retrieve basic information out of thedifferent CMA areas and to test allocation/release in each of the areas.Each CMA zone represents a directory under <debugfs>/cma/, indexed by thekernel's CMA index. So the first CMA zone would be: <debugfs>/cma/cma-0The 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/allocwould try to allocate 5 pages from the cma-2 area. - [WO] free: Free N pages from that CMA area, similar to the above.