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+What: /sys/class/bdi/<bdi>/
+Date: January 2008
+Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
+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.
+stable_pages_required (read-only)
+ If set, the backing device requires that all pages comprising a write
+ request must not be changed until writeout is complete.