Re: Zoned storage and BLK_STS_RESOURCE

[Jens Axboe <axboe@kernel.dk>]

On 12/17/24 1:59 PM, Damien Le Moal wrote:
> On 2024/12/17 11:58, Jens Axboe wrote:
>> On 12/17/24 12:54 PM, Jens Axboe wrote:
>>> io_uring does support ordering writes - not because of zoning, but to
>>> avoid buffered writes being spread over a bunch of threads and hence
>>> just hammering the inode mutex rather than doing actual useful work. You
>>> could potentially use that. Then all pending writes for that inode would
>>> be ordered, even if punted to io-wq.
>>
>> See io_uring/io_uring.c:io_prep_async_work(), which is called when an IO
>> is added for io-wq execution, io_wq_hash_work() makes sure it'll be
>> ordered. However, this will still not work if you're driving beyond the
>> limit of the device queue depth, or if you're doing IOs that may trigger
>> -EAGAIN spuriously for -EAGAIN as you can still have two issuers - the
>> task itself submitting IO, and the one io-wq worker tasked with doing
>> blocking writes on this zoned device.
> 
> Thanks for the pointer. Will have a look. It may be as simple as
> always using the io-wq worker for zone writes and have these ordered
> (__WQ_ORDERED). Maybe.

Right, that should work if you force everything to be served by io-wq
and ensure it's hashed.

-- 
Jens Axboe