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>/min_ratio_fine
48Date:		November 2022
49Contact:	Stefan Roesch <shr@devkernel.io>
50Description:
51	Under normal circumstances each device is given a part of the
52	total write-back cache that relates to its current average
53	writeout speed in relation to the other devices.
54
55	The 'min_ratio_fine' parameter allows assigning a minimum reserve
56	of the write-back cache to a particular device. The value is
57	expressed as part of 1 million. For example, this is useful for
58	providing a minimum QoS.
59
60	(read-write)
61
62What:		/sys/class/bdi/<bdi>/max_ratio
63Date:		January 2008
64Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
65Description:
66	Allows limiting a particular device to use not more than the
67	given percentage of the write-back cache.  This is useful in
68	situations where we want to avoid one device taking all or
69	most of the write-back cache.  For example in case of an NFS
70	mount that is prone to get stuck, or a FUSE mount which cannot
71	be trusted to play fair.
72
73	(read-write)
74
75What:		/sys/class/bdi/<bdi>/max_ratio_fine
76Date:		November 2022
77Contact:	Stefan Roesch <shr@devkernel.io>
78Description:
79	Allows limiting a particular device to use not more than the
80	given value of the write-back cache.  The value is given as part
81	of 1 million. This is useful in situations where we want to avoid
82	one device taking all or most of the write-back cache.  For example
83	in case of an NFS mount that is prone to get stuck, or a FUSE mount
84	which cannot be trusted to play fair.
85
86	(read-write)
87
88What:		/sys/class/bdi/<bdi>/min_bytes
89Date:		October 2022
90Contact:	Stefan Roesch <shr@devkernel.io>
91Description:
92	Under normal circumstances each device is given a part of the
93	total write-back cache that relates to its current average
94	writeout speed in relation to the other devices.
95
96	The 'min_bytes' parameter allows assigning a minimum
97	percentage of the write-back cache to a particular device
98	expressed in bytes.
99	For example, this is useful for providing a minimum QoS.
100
101	(read-write)
102
103What:		/sys/class/bdi/<bdi>/max_bytes
104Date:		October 2022
105Contact:	Stefan Roesch <shr@devkernel.io>
106Description:
107	Allows limiting a particular device to use not more than the
108	given 'max_bytes' of the write-back cache.  This is useful in
109	situations where we want to avoid one device taking all or
110	most of the write-back cache.  For example in case of an NFS
111	mount that is prone to get stuck, a FUSE mount which cannot be
112	trusted to play fair, or a nbd device.
113
114	(read-write)
115
116What:		/sys/class/bdi/<bdi>/strict_limit
117Date:		October 2022
118Contact:	Stefan Roesch <shr@devkernel.io>
119Description:
120	Forces per-BDI checks for the share of given device in the write-back
121	cache even before the global background dirty limit is reached. This
122	is useful in situations where the global limit is much higher than
123	affordable for given relatively slow (or untrusted) device. Turning
124	strictlimit on has no visible effect if max_ratio is equal to 100%.
125
126	(read-write)
127What:		/sys/class/bdi/<bdi>/stable_pages_required
128Date:		January 2008
129Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
130Description:
131	If set, the backing device requires that all pages comprising a write
132	request must not be changed until writeout is complete.
133
134	(read-only)
135