[mirror_ubuntu-bionic-kernel.git] / Documentation / ABI / testing / sysfs-class-bdi

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.

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.
Commit	Line	Data
cf0ca9fe PZ	1	What: /sys/class/bdi/<bdi>/
	2	Date: January 2008
	3	Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
	4	Description:
	5
76f1418b MS	6	Provide a place in sysfs for the backing_dev_info object. This allows
76f1418b MS	7	setting and retrieving various BDI specific variables.
cf0ca9fe PZ	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
03fb0bce MS	17	MAJOR:MINOR-fuseblk
	18
	19	Value of st_dev on fuseblk filesystems.
	20
cf0ca9fe PZ	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
189d3c4a PZ	33	min_ratio (read-write)
189d3c4a PZ	34
76f1418b MS	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.
a42dde04 PZ	42
	43	max_ratio (read-write)
	44
76f1418b MS	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.
7d311cda DW	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.