1What: /sys/class/bdi/<bdi>/ 2Date: January 2008 3Contact: Peter Zijlstra <a.p.zijlstra@chello.nl> 4Description: 5 6Provide a place in sysfs for the backing_dev_info object. This allows 7setting and retrieving various BDI specific variables. 8 9The <bdi> identifier can be either of the following: 10 11MAJOR: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 17MAJOR:MINOR-fuseblk 18 19 Value of st_dev on fuseblk filesystems. 20 21default 22 23 The default backing dev, used for non-block device backed 24 filesystems which do not provide their own BDI. 25 26Files under /sys/class/bdi/<bdi>/ 27--------------------------------- 28 29read_ahead_kb (read-write) 30 31 Size of the read-ahead window in kilobytes 32 33min_ratio (read-write) 34 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. 42 43max_ratio (read-write) 44 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. 51 52stable_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. 56