Hi and thanks! > LRU, same as bcache. do you plan to change this , since LRU is not very efficient (in comparison to other), maybe 2Q or ARC[1-4] > [...] > And you can pin specific files/folders to a device, by setting foreground target > to that device and setting background target and promote target to nothing. ok thank you very much! That must be documented somewhere ;-) [1] https://en.ru.is/media/skjol-td/cache_comparison.pdf [2] https://dbs.uni-leipzig.de/file/ARC.pdf [3] http://people.cs.vt.edu/~butta/docs/sigmetrics05_kernelPrefetch.pdf [4] http://www.vldb.org/conf/1994/P439.PDF On Thursday, July 9, 2020 12:37:29 AM CEST kent.overstreet@xxxxxxxxx wrote: > On Wed, Jul 08, 2020 at 11:46:00PM +0200, Stefan K wrote: > > Hello, > > > > short question: how does the caching works with bcachefs? Is it like "first > > in first out" or is it more complex like the ARC system in zfs? > > LRU, same as bcache. > > > The same with the write-cache, will be everything written to the SSD/NVMe > > (Cache) and then to the HDD? When will will the filesystem say "its written to > > disk"? And what happens with the data on the write cache if we have a > > powerfail? > > Disks that are used as caches are treated no differently from other disks by the > filesystem. If you want bcachefs to not rely on a specific disk, you can set its > durability to 0, and then it'll basically only be used as a writethrough cache. > > > > > And can I say have this file/folder always in the cache, while it works "normal" ? > > Yes. > > So caching is configured differently, specifically so that it can be configured > on a per file/directory basis. Instead of having a notion of "cache device", > there are options for > - foregroud target: which device or group of devices are used for foreground > writes > - background target: if enabled, the rebalance thread will in the background > move data to this target in the background, leaving a cached copy on the > foreground target > - promote target: if enabled, when data is read and it doesn't exist in this > target, a cached copy will be added there > > So these options can be set to get you writeback mode, by setting foreground > target and promote target to your SSD and background target to your HDD. > > And you can pin specific files/folders to a device, by setting foreground target > to that device and setting background target and promote target to nothing. >
