Ming Lei <ming.lei@xxxxxxxxxx> writes: > CAUTION: This email originated from outside of Western Digital. Do not click on > links or open attachments unless you recognize the sender and know that the > content is safe. > > > 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. You are right, it does not matter if the zone is implicitly closed, I was mistaken. But we still have to track the write pointer of every zone in open or active state, otherwise we cannot know if a write that arrive to a zone with no outstanding IO is actually at the write pointer, or whether we need to hold it. > >> >> > >> > 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. The current implementation _does_ break zoned write because it reverses batched writes. But if it is an easy fix, that is cool :) Best regards, Andreas
