1What:		/sys/class/bdi/<bdi>/
2Date:		January 2008
3Contact:	Peter Zijlstra <[email protected]>
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 <[email protected]>
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 <[email protected]>
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 <[email protected]>
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>/strict_limit
60Date:		October 2022
61Contact:	Stefan Roesch <[email protected]>
62Description:
63	Forces per-BDI checks for the share of given device in the write-back
64	cache even before the global background dirty limit is reached. This
65	is useful in situations where the global limit is much higher than
66	affordable for given relatively slow (or untrusted) device. Turning
67	strictlimit on has no visible effect if max_ratio is equal to 100%.
68
69	(read-write)
70What:		/sys/class/bdi/<bdi>/stable_pages_required
71Date:		January 2008
72Contact:	Peter Zijlstra <[email protected]>
73Description:
74	If set, the backing device requires that all pages comprising a write
75	request must not be changed until writeout is complete.
76
77	(read-only)
78