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-What: /sys/class/bdi/<bdi>/
-Date: January 2008
-Contact: Peter Zijlstra <>
-Provide a place in sysfs for the backing_dev_info object. This allows
-setting and retrieving various BDI specific variables.
-The <bdi> identifier can be either of the following:
- Device number for block devices, or value of st_dev on
- non-block filesystems which provide their own BDI, such as NFS
- and FUSE.
- Value of st_dev on fuseblk filesystems.
- The default backing dev, used for non-block device backed
- filesystems which do not provide their own BDI.
-Files under /sys/class/bdi/<bdi>/
-read_ahead_kb (read-write)
- Size of the read-ahead window in kilobytes
-min_ratio (read-write)
- Under normal circumstances each device is given a part of the
- total write-back cache that relates to its current average
- writeout speed in relation to the other devices.
- The 'min_ratio' parameter allows assigning a minimum
- percentage of the write-back cache to a particular device.
- For example, this is useful for providing a minimum QoS.
-max_ratio (read-write)
- Allows limiting a particular device to use not more than the
- given percentage of the write-back cache. This is useful in
- situations where we want to avoid one device taking all or
- most of the write-back cache. For example in case of an NFS
- mount that is prone to get stuck, or a FUSE mount which cannot
- be trusted to play fair.