1 What: /sys/class/bdi/<bdi>/
3 Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
6 Provide a place in sysfs for the backing_dev_info object. This allows
7 setting and retrieving various BDI specific variables.
9 The <bdi> identifier can be either of the following:
13 Device number for block devices, or value of st_dev on
14 non-block filesystems which provide their own BDI, such as NFS
19 Value of st_dev on fuseblk filesystems.
23 The default backing dev, used for non-block device backed
24 filesystems which do not provide their own BDI.
26 Files under /sys/class/bdi/<bdi>/
27 ---------------------------------
29 read_ahead_kb (read-write)
31 Size of the read-ahead window in kilobytes
33 min_ratio (read-write)
35 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.
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.
43 max_ratio (read-write)
45 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.
52 stable_pages_required (read-only)
54 If set, the backing device requires that all pages comprising a write
55 request must not be changed until writeout is complete.
57 strictlimit (read-write)
59 Forces per-BDI checks for the share of given device in the write-back
60 cache even before the global background dirty limit is reached. This
61 is useful in situations where the global limit is much higher than
62 affordable for given relatively slow (or untrusted) device. Turning
63 strictlimit on has no visible effect if max_ratio is equal to 100%.