What: /sys/class/bdi// Date: January 2008 Contact: Peter Zijlstra Description: Provide a place in sysfs for the backing_dev_info object. This allows setting and retrieving various BDI specific variables. The 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// --------------------------------- 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. strictlimit (read-write) Forces per-BDI checks for the share of given device in the write-back cache even before the global background dirty limit is reached. This is useful in situations where the global limit is much higher than affordable for given relatively slow (or untrusted) device. Turning strictlimit on has no visible effect if max_ratio is equal to 100%.