xref: /openbmc/linux/Documentation/ABI/testing/sysfs-class-bdi (revision 7ae9fb1b7ecbb5d85d07857943f677fd1a559b18)
1 What:		/sys/class/bdi/<bdi>/
2 Date:		January 2008
3 Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
4 Description:
5 
6 Provide a place in sysfs for the backing_dev_info object.  This allows
7 setting and retrieving various BDI specific variables.
8 
9 The <bdi> identifier can be either of the following:
10 
11 MAJOR: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 
17 MAJOR:MINOR-fuseblk
18 
19 	Value of st_dev on fuseblk filesystems.
20 
21 default
22 
23 	The default backing dev, used for non-block device backed
24 	filesystems which do not provide their own BDI.
25 
26 What:		/sys/class/bdi/<bdi>/read_ahead_kb
27 Date:		January 2008
28 Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
29 Description:
30 	Size of the read-ahead window in kilobytes
31 
32 	(read-write)
33 What:		/sys/class/bdi/<bdi>/min_ratio
34 Date:		January 2008
35 Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
36 Description:
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 
47 What:		/sys/class/bdi/<bdi>/min_ratio_fine
48 Date:		November 2022
49 Contact:	Stefan Roesch <shr@devkernel.io>
50 Description:
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 
62 What:		/sys/class/bdi/<bdi>/max_ratio
63 Date:		January 2008
64 Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
65 Description:
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 
75 What:		/sys/class/bdi/<bdi>/max_ratio_fine
76 Date:		November 2022
77 Contact:	Stefan Roesch <shr@devkernel.io>
78 Description:
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 
88 What:		/sys/class/bdi/<bdi>/min_bytes
89 Date:		October 2022
90 Contact:	Stefan Roesch <shr@devkernel.io>
91 Description:
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 
103 What:		/sys/class/bdi/<bdi>/max_bytes
104 Date:		October 2022
105 Contact:	Stefan Roesch <shr@devkernel.io>
106 Description:
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 
116 What:		/sys/class/bdi/<bdi>/strict_limit
117 Date:		October 2022
118 Contact:	Stefan Roesch <shr@devkernel.io>
119 Description:
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)
127 What:		/sys/class/bdi/<bdi>/stable_pages_required
128 Date:		January 2008
129 Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
130 Description:
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