1What:		/sys/class/bdi/<bdi>/
2Date:		January 2008
3Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
4Description:
5
6Provide a place in sysfs for the backing_dev_info object.  This allows
7setting and retrieving various BDI specific variables.
8
9The <bdi> identifier can be either of the following:
10
11MAJOR:MINOR
12
13	Device number for block devices, or value of st_dev on
14	non-block filesystems which provide their own BDI, such as NFS
15	and FUSE.
16
17MAJOR:MINOR-fuseblk
18
19	Value of st_dev on fuseblk filesystems.
20
21default
22
23	The default backing dev, used for non-block device backed
24	filesystems which do not provide their own BDI.
25
26What:		/sys/class/bdi/<bdi>/read_ahead_kb
27Date:		January 2008
28Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
29Description:
30	Size of the read-ahead window in kilobytes
31
32	(read-write)
33What:		/sys/class/bdi/<bdi>/min_ratio
34Date:		January 2008
35Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
36Description:
37	Under normal circumstances each device is given a part of the
38	total write-back cache that relates to its current average
39	writeout speed in relation to the other devices.
40
41	The 'min_ratio' parameter allows assigning a minimum
42	percentage of the write-back cache to a particular device.
43	For example, this is useful for providing a minimum QoS.
44
45	(read-write)
46
47What:		/sys/class/bdi/<bdi>/max_ratio
48Date:		January 2008
49Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
50Description:
51	Allows limiting a particular device to use not more than the
52	given percentage of the write-back cache.  This is useful in
53	situations where we want to avoid one device taking all or
54	most of the write-back cache.  For example in case of an NFS
55	mount that is prone to get stuck, or a FUSE mount which cannot
56	be trusted to play fair.
57
58	(read-write)
59What:		/sys/class/bdi/<bdi>/stable_pages_required
60Date:		January 2008
61Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
62Description:
63	If set, the backing device requires that all pages comprising a write
64	request must not be changed until writeout is complete.
65
66	(read-only)
67