1cf0ca9feSPeter ZijlstraWhat:		/sys/class/bdi/<bdi>/
2cf0ca9feSPeter ZijlstraDate:		January 2008
3cf0ca9feSPeter ZijlstraContact:	Peter Zijlstra <a.p.zijlstra@chello.nl>
4cf0ca9feSPeter ZijlstraDescription:
5cf0ca9feSPeter Zijlstra
6*76f1418bSMiklos SzerediProvide a place in sysfs for the backing_dev_info object.  This allows
7*76f1418bSMiklos Szeredisetting and retrieving various BDI specific variables.
8cf0ca9feSPeter Zijlstra
9cf0ca9feSPeter ZijlstraThe <bdi> identifier can be either of the following:
10cf0ca9feSPeter Zijlstra
11cf0ca9feSPeter ZijlstraMAJOR:MINOR
12cf0ca9feSPeter Zijlstra
13cf0ca9feSPeter Zijlstra	Device number for block devices, or value of st_dev on
14cf0ca9feSPeter Zijlstra	non-block filesystems which provide their own BDI, such as NFS
15cf0ca9feSPeter Zijlstra	and FUSE.
16cf0ca9feSPeter Zijlstra
17cf0ca9feSPeter Zijlstradefault
18cf0ca9feSPeter Zijlstra
19cf0ca9feSPeter Zijlstra	The default backing dev, used for non-block device backed
20cf0ca9feSPeter Zijlstra	filesystems which do not provide their own BDI.
21cf0ca9feSPeter Zijlstra
22cf0ca9feSPeter ZijlstraFiles under /sys/class/bdi/<bdi>/
23cf0ca9feSPeter Zijlstra---------------------------------
24cf0ca9feSPeter Zijlstra
25cf0ca9feSPeter Zijlstraread_ahead_kb (read-write)
26cf0ca9feSPeter Zijlstra
27cf0ca9feSPeter Zijlstra	Size of the read-ahead window in kilobytes
28cf0ca9feSPeter Zijlstra
29189d3c4aSPeter Zijlstramin_ratio (read-write)
30189d3c4aSPeter Zijlstra
31*76f1418bSMiklos Szeredi	Under normal circumstances each device is given a part of the
32*76f1418bSMiklos Szeredi	total write-back cache that relates to its current average
33*76f1418bSMiklos Szeredi	writeout speed in relation to the other devices.
34*76f1418bSMiklos Szeredi
35*76f1418bSMiklos Szeredi	The 'min_ratio' parameter allows assigning a minimum
36*76f1418bSMiklos Szeredi	percentage of the write-back cache to a particular device.
37*76f1418bSMiklos Szeredi	For example, this is useful for providing a minimum QoS.
38a42dde04SPeter Zijlstra
39a42dde04SPeter Zijlstramax_ratio (read-write)
40a42dde04SPeter Zijlstra
41*76f1418bSMiklos Szeredi	Allows limiting a particular device to use not more than the
42*76f1418bSMiklos Szeredi	given percentage of the write-back cache.  This is useful in
43*76f1418bSMiklos Szeredi	situations where we want to avoid one device taking all or
44*76f1418bSMiklos Szeredi	most of the write-back cache.  For example in case of an NFS
45*76f1418bSMiklos Szeredi	mount that is prone to get stuck, or a FUSE mount which cannot
46*76f1418bSMiklos Szeredi	be trusted to play fair.
47