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CMA Debugfs Interface
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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 area represents a directory under <debugfs>/cma/, represented by
its CMA name like below:

	<debugfs>/cma/<cma_name>

The structure of the files created under that directory is as follows:

 - [RO] base_pfn: The base PFN (Page Frame Number) of the CMA area.
        This is the same as ranges/0/base_pfn.
 - [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 allocated pages in the area.
        This is the same as ranges/0/base_pfn.
 - [RO] ranges/N/base_pfn: The base PFN of contiguous range N
        in the CMA area.
 - [RO] ranges/N/bitmap: The bit map of allocated pages in
        range N in the CMA area.
 - [WO] alloc: Allocate N pages from that CMA area. For example::

	echo 5 > <debugfs>/cma/<cma_name>/alloc

would try to allocate 5 pages from the 'cma_name' area.

 - [WO] free: Free N pages from that CMA area, similar to the above.