On 12/7/23 17:37, Damien Le Moal wrote:
On 12/8/23 09:03, Bart Van Assche wrote:+static bool dd_use_io_priority(struct deadline_data *dd, enum req_op op) +{ + return dd->prio_aging_expire != 0 && !op_needs_zoned_write_locking(op); +}Hard NACK on this. The reason is that this will disable IO priority also for sensible use cases that use libaio/io_uring with direct IOs, with an application that does the right thing for writes, namely assigning the same priority for all writes to a zone. There are some use cases like this in production. I do understand that there is a problem when IO priorities come from cgroups and the user go through a file system. But that should be handled by the file system. That is, for f2fs, all writes going to the same zone should have the same priority. Otherwise, priority inversion issues will lead to non sequential write patterns. Ideally, we should indeed have a generic solution for the cgroup case. But it seems that for now, the simplest thing to do is to not allow priorities through cgroups for writes to zoned devices, unless cgroups is made more intellignet about it and manage bio priorities per zone to avoid priority inversion within a zone.
Hi Damien, My understanding is that blkcg_set_ioprio() is called from inside submit_bio() and hence that the reported issue cannot be solved by modifying F2FS. How about modifying the blk-ioprio policy such that it ignores zoned writes? Thanks, Bart.
