Documentation/ABI/testing/sysfs-class-bdi

   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 Files under /sys/class/bdi/<bdi>/
  27 ---------------------------------
  28
  29 read_ahead_kb (read-write)
  30
  31         Size of the read-ahead window in kilobytes
  32
  33 min_ratio (read-write)
  34
  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.
  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.
  42
  43 max_ratio (read-write)
  44
  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.
  51
  52 stable_pages_required (read-only)
  53
  54         If set, the backing device requires that all pages comprising a write
  55         request must not be changed until writeout is complete.