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
17default
18
19	The default backing dev, used for non-block device backed
20	filesystems which do not provide their own BDI.
21
22Files under /sys/class/bdi/<bdi>/
23---------------------------------
24
25read_ahead_kb (read-write)
26
27	Size of the read-ahead window in kilobytes
28
29min_ratio (read-write)
30
31	Under normal circumstances each device is given a part of the
32	total write-back cache that relates to its current average
33	writeout speed in relation to the other devices.
34
35	The 'min_ratio' parameter allows assigning a minimum
36	percentage of the write-back cache to a particular device.
37	For example, this is useful for providing a minimum QoS.
38
39max_ratio (read-write)
40
41	Allows limiting a particular device to use not more than the
42	given percentage of the write-back cache.  This is useful in
43	situations where we want to avoid one device taking all or
44	most of the write-back cache.  For example in case of an NFS
45	mount that is prone to get stuck, or a FUSE mount which cannot
46	be trusted to play fair.
47