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
setting and retrieving 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.

MAJOR:MINOR-fuseblk

	Value of st_dev on fuseblk filesystems.

default

	The default backing dev, used for non-block device backed
	filesystems which do not provide their own BDI.

What:		/sys/class/bdi/<bdi>/read_ahead_kb
Date:		January 2008
Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
Description:
	Size of the read-ahead window in kilobytes

	(read-write)
What:		/sys/class/bdi/<bdi>/min_ratio
Date:		January 2008
Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
Description:
	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.

	(read-write)

What:		/sys/class/bdi/<bdi>/max_ratio
Date:		January 2008
Contact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
Description:
	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.

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

	(read-only)