On 2021/04/20 10:20, Douglas Gilbert wrote: > On 2021-04-19 2:45 a.m., Christoph Hellwig wrote: >> On Sat, Apr 17, 2021 at 11:33:23AM +0900, Damien Le Moal wrote: >>> Synchronous writes to sequential zone files cannot use zone append >>> operations if the underlying zoned device queue limit >>> max_zone_append_sectors is 0, indicating that the device does not >>> support this operation. In this case, fall back to using regular write >>> operations. >> >> Zone append is a mandatory feature of the zoned device API. > > So a hack required for ZNS and not needed by ZBC and ZAC becomes > a "mandatory feature" in a Linux API. Like many hacks, that one might > come back to bite you :-) Zone append is not a hack in ZNS. It is a write interface that fits very well with the multi-queue nature of NVMe. The "hack" is the emulation in scsi. We decided on having this mandatory for zoned devices (all types) to make sure that file systems do not have to implement different IO paths for sequential writing to zones. Zone append does simplify a lot of things and allows to get the best performance from ZNS drives. Zone write locking/serialization of writes per zones using regular writes is much harder to implement, make a mess of the file system code, and would kill write performance on ZNS. -- Damien Le Moal Western Digital Research
