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+What:           /sys/class/bdi/<bdi>/
+Date:           January 2008
+Contact:        Peter Zijlstra <a.p.zijlstra@chello.nl>
+Description:
+
+Provide a place in sysfs for the backing_dev_info object.
+This allows us to see and set the various BDI specific variables.
+
+The <bdi> identifier can be either of the following:
+
+MAJOR:MINOR
+
+        Device number for block devices, or value of st_dev on
+        non-block filesystems which provide their own BDI, such as NFS
+        and FUSE.
+
+default
+
+        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
+
+reclaimable_kb (read-only)
+
+        Reclaimable (dirty or unstable) memory destined for writeback
+        to this device
+
+writeback_kb (read-only)
+
+        Memory currently under writeback to this device
+
+dirty_kb (read-only)
+
+        Global threshold for reclaimable + writeback memory
+
+bdi_dirty_kb (read-only)
+
+        Current threshold on this BDI for reclaimable + writeback
+        memory
+