>>>>> "Eric" == Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> writes: Eric, Eric> However, just because FADV_SEQUENTIAL is flagged doesn't mean the Eric> cache should bypass. Filesystems can fragment, and while the file Eric> being read may be read sequentially, the blocks on which it Eric> resides may not be. Same thing for higher-level block devices Eric> such as dm-thinp where one might sequentially read a thin volume Eric> but its _tdata might not be in linear order. This may imply that Eric> we need a new way to flag cache bypass from userspace that is Eric> neither io-priority nor fadvise driven. Why conflate the two? Something being a background task is orthogonal to whether it is being read sequentially or not. Eric> So what are our options? What might be the best way to do this? For the SCSI I/O hints I use the idle I/O priority to classify backups. Works fine. Eric> Are FADV_NOREUSE/FADV_DONTNEED reasonable candidates? FADV_DONTNEED was intended for this. There have been patches posted in the past that tied the loop between the fadvise flags and the bio. I would like to see those revived. Eric> Perhaps ionice could be used used, but the concept of "priority" Eric> doesn't exactly encompass the concept of cache-bypass---so is Eric> something else needed? The idle class explicitly does not have a priority. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
