1*4882a593SmuzhiyunWhat: /sys/class/bdi/<bdi>/ 2*4882a593SmuzhiyunDate: January 2008 3*4882a593SmuzhiyunContact: Peter Zijlstra <a.p.zijlstra@chello.nl> 4*4882a593SmuzhiyunDescription: 5*4882a593Smuzhiyun 6*4882a593SmuzhiyunProvide a place in sysfs for the backing_dev_info object. This allows 7*4882a593Smuzhiyunsetting and retrieving various BDI specific variables. 8*4882a593Smuzhiyun 9*4882a593SmuzhiyunThe <bdi> identifier can be either of the following: 10*4882a593Smuzhiyun 11*4882a593SmuzhiyunMAJOR:MINOR 12*4882a593Smuzhiyun 13*4882a593Smuzhiyun Device number for block devices, or value of st_dev on 14*4882a593Smuzhiyun non-block filesystems which provide their own BDI, such as NFS 15*4882a593Smuzhiyun and FUSE. 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunMAJOR:MINOR-fuseblk 18*4882a593Smuzhiyun 19*4882a593Smuzhiyun Value of st_dev on fuseblk filesystems. 20*4882a593Smuzhiyun 21*4882a593Smuzhiyundefault 22*4882a593Smuzhiyun 23*4882a593Smuzhiyun The default backing dev, used for non-block device backed 24*4882a593Smuzhiyun filesystems which do not provide their own BDI. 25*4882a593Smuzhiyun 26*4882a593SmuzhiyunFiles under /sys/class/bdi/<bdi>/ 27*4882a593Smuzhiyun 28*4882a593Smuzhiyunread_ahead_kb (read-write) 29*4882a593Smuzhiyun 30*4882a593Smuzhiyun Size of the read-ahead window in kilobytes 31*4882a593Smuzhiyun 32*4882a593Smuzhiyunmin_ratio (read-write) 33*4882a593Smuzhiyun 34*4882a593Smuzhiyun Under normal circumstances each device is given a part of the 35*4882a593Smuzhiyun total write-back cache that relates to its current average 36*4882a593Smuzhiyun writeout speed in relation to the other devices. 37*4882a593Smuzhiyun 38*4882a593Smuzhiyun The 'min_ratio' parameter allows assigning a minimum 39*4882a593Smuzhiyun percentage of the write-back cache to a particular device. 40*4882a593Smuzhiyun For example, this is useful for providing a minimum QoS. 41*4882a593Smuzhiyun 42*4882a593Smuzhiyunmax_ratio (read-write) 43*4882a593Smuzhiyun 44*4882a593Smuzhiyun Allows limiting a particular device to use not more than the 45*4882a593Smuzhiyun given percentage of the write-back cache. This is useful in 46*4882a593Smuzhiyun situations where we want to avoid one device taking all or 47*4882a593Smuzhiyun most of the write-back cache. For example in case of an NFS 48*4882a593Smuzhiyun mount that is prone to get stuck, or a FUSE mount which cannot 49*4882a593Smuzhiyun be trusted to play fair. 50*4882a593Smuzhiyun 51*4882a593Smuzhiyunstable_pages_required (read-only) 52*4882a593Smuzhiyun 53*4882a593Smuzhiyun If set, the backing device requires that all pages comprising a write 54*4882a593Smuzhiyun request must not be changed until writeout is complete. 55