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Peter Zijlstracf0ca9f2008-04-30 00:54:32 -07001What: /sys/class/bdi/<bdi>/
2Date: January 2008
3Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
4Description:
5
Miklos Szeredi76f14182008-04-30 00:54:36 -07006Provide a place in sysfs for the backing_dev_info object. This allows
7setting and retrieving various BDI specific variables.
Peter Zijlstracf0ca9f2008-04-30 00:54:32 -07008
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
Miklos Szeredi03fb0bc2008-05-23 13:04:19 -070017MAJOR:MINOR-fuseblk
18
19 Value of st_dev on fuseblk filesystems.
20
Peter Zijlstracf0ca9f2008-04-30 00:54:32 -070021default
22
23 The default backing dev, used for non-block device backed
24 filesystems which do not provide their own BDI.
25
26Files under /sys/class/bdi/<bdi>/
27---------------------------------
28
29read_ahead_kb (read-write)
30
31 Size of the read-ahead window in kilobytes
32
Peter Zijlstra189d3c42008-04-30 00:54:35 -070033min_ratio (read-write)
34
Miklos Szeredi76f14182008-04-30 00:54:36 -070035 Under normal circumstances each device is given a part of the
36 total write-back cache that relates to its current average
37 writeout speed in relation to the other devices.
38
39 The 'min_ratio' parameter allows assigning a minimum
40 percentage of the write-back cache to a particular device.
41 For example, this is useful for providing a minimum QoS.
Peter Zijlstraa42dde02008-04-30 00:54:36 -070042
43max_ratio (read-write)
44
Miklos Szeredi76f14182008-04-30 00:54:36 -070045 Allows limiting a particular device to use not more than the
46 given percentage of the write-back cache. This is useful in
47 situations where we want to avoid one device taking all or
48 most of the write-back cache. For example in case of an NFS
49 mount that is prone to get stuck, or a FUSE mount which cannot
50 be trusted to play fair.