[linux-block.git] / Documentation / admin-guide / mm / cma_debugfs.rst

=====================
CMA Debugfs Interface
=====================

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 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_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.
Commit	Line	Data
01c0aa79 MCC	1	=====================
	2	CMA Debugfs Interface
	3	=====================
	4
17e0db82 SL	5	The CMA debugfs interface is useful to retrieve basic information out of the
	6	different CMA areas and to test allocation/release in each of the areas.
	7
9a79443d CTK	8	Each CMA area represents a directory under <debugfs>/cma/, represented by
9a79443d CTK	9	its CMA name like below:
17e0db82	10
9a79443d	11	<debugfs>/cma/<cma_name>
17e0db82 SL	12
	13	The structure of the files created under that directory is as follows:
	14
	15	- [RO] base_pfn: The base PFN (Page Frame Number) of the zone.
	16	- [RO] count: Amount of memory in the CMA area.
	17	- [RO] order_per_bit: Order of pages represented by one bit.
	18	- [RO] bitmap: The bitmap of page states in the zone.
01c0aa79	19	- [WO] alloc: Allocate N pages from that CMA area. For example::
17e0db82	20
9a79443d	21	echo 5 > <debugfs>/cma/<cma_name>/alloc
17e0db82	22
9a79443d	23	would try to allocate 5 pages from the 'cma_name' area.
17e0db82 SL	24
17e0db82 SL	25	- [WO] free: Free N pages from that CMA area, similar to the above.