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
26Files under /sys/class/bdi/<bdi>/
27
28read_ahead_kb (read-write)
29
30	Size of the read-ahead window in kilobytes
31
32min_ratio (read-write)
33
34	Under normal circumstances each device is given a part of the
35	total write-back cache that relates to its current average
36	writeout speed in relation to the other devices.
37
38	The 'min_ratio' parameter allows assigning a minimum
39	percentage of the write-back cache to a particular device.
40	For example, this is useful for providing a minimum QoS.
41
42max_ratio (read-write)
43
44	Allows limiting a particular device to use not more than the
45	given percentage of the write-back cache.  This is useful in
46	situations where we want to avoid one device taking all or
47	most of the write-back cache.  For example in case of an NFS
48	mount that is prone to get stuck, or a FUSE mount which cannot
49	be trusted to play fair.
50
51stable_pages_required (read-only)
52
53	If set, the backing device requires that all pages comprising a write
54	request must not be changed until writeout is complete.
55