18c2ecf20Sopenharmony_ciWhat: /sys/class/bdi/<bdi>/ 28c2ecf20Sopenharmony_ciDate: January 2008 38c2ecf20Sopenharmony_ciContact: Peter Zijlstra <a.p.zijlstra@chello.nl> 48c2ecf20Sopenharmony_ciDescription: 58c2ecf20Sopenharmony_ci 68c2ecf20Sopenharmony_ciProvide a place in sysfs for the backing_dev_info object. This allows 78c2ecf20Sopenharmony_cisetting and retrieving various BDI specific variables. 88c2ecf20Sopenharmony_ci 98c2ecf20Sopenharmony_ciThe <bdi> identifier can be either of the following: 108c2ecf20Sopenharmony_ci 118c2ecf20Sopenharmony_ciMAJOR:MINOR 128c2ecf20Sopenharmony_ci 138c2ecf20Sopenharmony_ci Device number for block devices, or value of st_dev on 148c2ecf20Sopenharmony_ci non-block filesystems which provide their own BDI, such as NFS 158c2ecf20Sopenharmony_ci and FUSE. 168c2ecf20Sopenharmony_ci 178c2ecf20Sopenharmony_ciMAJOR:MINOR-fuseblk 188c2ecf20Sopenharmony_ci 198c2ecf20Sopenharmony_ci Value of st_dev on fuseblk filesystems. 208c2ecf20Sopenharmony_ci 218c2ecf20Sopenharmony_cidefault 228c2ecf20Sopenharmony_ci 238c2ecf20Sopenharmony_ci The default backing dev, used for non-block device backed 248c2ecf20Sopenharmony_ci filesystems which do not provide their own BDI. 258c2ecf20Sopenharmony_ci 268c2ecf20Sopenharmony_ciFiles under /sys/class/bdi/<bdi>/ 278c2ecf20Sopenharmony_ci 288c2ecf20Sopenharmony_ciread_ahead_kb (read-write) 298c2ecf20Sopenharmony_ci 308c2ecf20Sopenharmony_ci Size of the read-ahead window in kilobytes 318c2ecf20Sopenharmony_ci 328c2ecf20Sopenharmony_cimin_ratio (read-write) 338c2ecf20Sopenharmony_ci 348c2ecf20Sopenharmony_ci Under normal circumstances each device is given a part of the 358c2ecf20Sopenharmony_ci total write-back cache that relates to its current average 368c2ecf20Sopenharmony_ci writeout speed in relation to the other devices. 378c2ecf20Sopenharmony_ci 388c2ecf20Sopenharmony_ci The 'min_ratio' parameter allows assigning a minimum 398c2ecf20Sopenharmony_ci percentage of the write-back cache to a particular device. 408c2ecf20Sopenharmony_ci For example, this is useful for providing a minimum QoS. 418c2ecf20Sopenharmony_ci 428c2ecf20Sopenharmony_cimax_ratio (read-write) 438c2ecf20Sopenharmony_ci 448c2ecf20Sopenharmony_ci Allows limiting a particular device to use not more than the 458c2ecf20Sopenharmony_ci given percentage of the write-back cache. This is useful in 468c2ecf20Sopenharmony_ci situations where we want to avoid one device taking all or 478c2ecf20Sopenharmony_ci most of the write-back cache. For example in case of an NFS 488c2ecf20Sopenharmony_ci mount that is prone to get stuck, or a FUSE mount which cannot 498c2ecf20Sopenharmony_ci be trusted to play fair. 508c2ecf20Sopenharmony_ci 518c2ecf20Sopenharmony_cistable_pages_required (read-only) 528c2ecf20Sopenharmony_ci 538c2ecf20Sopenharmony_ci If set, the backing device requires that all pages comprising a write 548c2ecf20Sopenharmony_ci request must not be changed until writeout is complete. 55