| 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. |
| |
| 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. |