| What: /sys/class/bdi/<bdi>/ | |
| Date: January 2008 | |
| Contact: Peter Zijlstra <a.p.zijlstra@chello.nl> | |
| Description: | |
| Provide a place in sysfs for the backing_dev_info object. This allows | |
| setting and retrieving various BDI specific variables. | |
| The <bdi> 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/<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. |