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)
59
60What:		/sys/class/bdi/<bdi>/min_bytes
61Date:		October 2022
62Contact:	Stefan Roesch <[email protected]>
63Description:
64	Under normal circumstances each device is given a part of the
65	total write-back cache that relates to its current average
66	writeout speed in relation to the other devices.
67
68	The 'min_bytes' parameter allows assigning a minimum
69	percentage of the write-back cache to a particular device
70	expressed in bytes.
71	For example, this is useful for providing a minimum QoS.
72
73	(read-write)
74
75What:		/sys/class/bdi/<bdi>/max_bytes
76Date:		October 2022
77Contact:	Stefan Roesch <[email protected]>
78Description:
79	Allows limiting a particular device to use not more than the
80	given 'max_bytes' of the write-back cache.  This is useful in
81	situations where we want to avoid one device taking all or
82	most of the write-back cache.  For example in case of an NFS
83	mount that is prone to get stuck, a FUSE mount which cannot be
84	trusted to play fair, or a nbd device.
85
86	(read-write)
87
88What:		/sys/class/bdi/<bdi>/strict_limit
89Date:		October 2022
90Contact:	Stefan Roesch <[email protected]>
91Description:
92	Forces per-BDI checks for the share of given device in the write-back
93	cache even before the global background dirty limit is reached. This
94	is useful in situations where the global limit is much higher than
95	affordable for given relatively slow (or untrusted) device. Turning
96	strictlimit on has no visible effect if max_ratio is equal to 100%.
97
98	(read-write)
99What:		/sys/class/bdi/<bdi>/stable_pages_required
100Date:		January 2008
101Contact:	Peter Zijlstra <[email protected]>
102Description:
103	If set, the backing device requires that all pages comprising a write
104	request must not be changed until writeout is complete.
105
106	(read-only)
107