On Fri, Nov 18, 2022 at 01:35:29PM +0900, Damien Le Moal wrote: > On 11/18/22 13:12, Ming Lei wrote: > [...] > >>> You can only assign it to zoned write request, but you still have to check > >>> the sequence inside each zone, right? Then why not just check LBAs in > >>> each zone simply? > >> > >> We would need to know the zone map, which is not otherwise required. > >> Then we would need to track the write pointer for each open zone for > >> each queue, so that we can stall writes that are not issued at the write > >> pointer. This is in effect all zones, because we cannot track when zones > >> are implicitly closed. Then, if different queues are issuing writes to > > > > Can you explain "implicitly closed" state a bit? > > > > From https://zonedstorage.io/docs/introduction/zoned-storage, only the > > following words are mentioned about closed state: > > > > ```Conversely, implicitly or explicitly opened zoned can be transitioned to the > > closed state using the CLOSE ZONE command.``` > > When a write is issued to an empty or closed zone, the drive will > automatically transition the zone into the implicit open state. This is > called implicit open because the host did not (explicitly) issue an open > zone command. > > When there are too many implicitly open zones, the drive may choose to > close one of the implicitly opened zone to implicitly open the zone that > is a target for a write command. > > Simple in a nutshell. This is done so that the drive can work with a > limited set of resources needed to handle open zones, that is, zones that > are being written. There are some more nasty details to all this with > limits on the number of open zones and active zones that a zoned drive may > have. OK, thanks for the clarification about implicitly closed, but I understand this close can't change the zone's write pointer. > > > > > zone info can be cached in the mapping(hash table)(zone sector is the key, and zone > > info is the value), which can be implemented as one LRU style. If any zone > > info isn't hit in the mapping table, ioctl(BLKREPORTZONE) can be called for > > obtaining the zone info. > > > >> the same zone, we need to sync across queues. Userspace may have > >> synchronization in place to issue writes with multiple threads while > >> still hitting the write pointer. > > > > You can trust mq-dealine, which guaranteed that write IO is sent to ->queue_rq() > > in order, no matter MQ or SQ. > > > > Yes, it could be issue from multiple queues for ublksrv, which doesn't sync > > among multiple queues. > > > > But per-zone re-order still can solve the issue, just need one lock > > for each zone to cover the MQ re-order. > > That lock is already there and using it, mq-deadline will never dispatch > more than one write per zone at any time. This is to avoid write > reordering. So multi queue or not, for any zone, there is no possibility > of having writes reordered. oops, I miss the single queue depth point per zone, so ublk won't break zoned write at all, and I agree order of batch IOs is one problem, but not hard to solve. Thanks, Ming
