1cf0ca9feSPeter ZijlstraWhat: /sys/class/bdi/<bdi>/ 2cf0ca9feSPeter ZijlstraDate: January 2008 3cf0ca9feSPeter ZijlstraContact: Peter Zijlstra <a.p.zijlstra@chello.nl> 4cf0ca9feSPeter ZijlstraDescription: 5cf0ca9feSPeter Zijlstra 676f1418bSMiklos SzerediProvide a place in sysfs for the backing_dev_info object. This allows 776f1418bSMiklos 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 17*03fb0bceSMiklos SzerediMAJOR:MINOR-fuseblk 18*03fb0bceSMiklos Szeredi 19*03fb0bceSMiklos Szeredi Value of st_dev on fuseblk filesystems. 20*03fb0bceSMiklos Szeredi 21cf0ca9feSPeter Zijlstradefault 22cf0ca9feSPeter Zijlstra 23cf0ca9feSPeter Zijlstra The default backing dev, used for non-block device backed 24cf0ca9feSPeter Zijlstra filesystems which do not provide their own BDI. 25cf0ca9feSPeter Zijlstra 26cf0ca9feSPeter ZijlstraFiles under /sys/class/bdi/<bdi>/ 27cf0ca9feSPeter Zijlstra--------------------------------- 28cf0ca9feSPeter Zijlstra 29cf0ca9feSPeter Zijlstraread_ahead_kb (read-write) 30cf0ca9feSPeter Zijlstra 31cf0ca9feSPeter Zijlstra Size of the read-ahead window in kilobytes 32cf0ca9feSPeter Zijlstra 33189d3c4aSPeter Zijlstramin_ratio (read-write) 34189d3c4aSPeter Zijlstra 3576f1418bSMiklos Szeredi Under normal circumstances each device is given a part of the 3676f1418bSMiklos Szeredi total write-back cache that relates to its current average 3776f1418bSMiklos Szeredi writeout speed in relation to the other devices. 3876f1418bSMiklos Szeredi 3976f1418bSMiklos Szeredi The 'min_ratio' parameter allows assigning a minimum 4076f1418bSMiklos Szeredi percentage of the write-back cache to a particular device. 4176f1418bSMiklos Szeredi For example, this is useful for providing a minimum QoS. 42a42dde04SPeter Zijlstra 43a42dde04SPeter Zijlstramax_ratio (read-write) 44a42dde04SPeter Zijlstra 4576f1418bSMiklos Szeredi Allows limiting a particular device to use not more than the 4676f1418bSMiklos Szeredi given percentage of the write-back cache. This is useful in 4776f1418bSMiklos Szeredi situations where we want to avoid one device taking all or 4876f1418bSMiklos Szeredi most of the write-back cache. For example in case of an NFS 4976f1418bSMiklos Szeredi mount that is prone to get stuck, or a FUSE mount which cannot 5076f1418bSMiklos Szeredi be trusted to play fair. 51