Re: [PATCH v12 2/2] fuse: add default_request_timeout and max_request_timeout sysctls

Bernd Schubert
2025-01-23T18:06:54Z

On 1/23/25 18:48, Joanne Koong wrote:
> On Thu, Jan 23, 2025 at 9:19 AM Bernd Schubert
> <bernd.schubert@fastmail.fm> wrote:
>>
>> Hi Joanne,
>>
>>>>> Thanks, applied and pushed with some cleanups including Luis's clamp idea.
>>>>
>>>> Hi Miklos,
>>>>
>>>> I don't think the timeouts do work with io-uring yet, I'm not sure
>>>> yet if I have time to work on that today or tomorrow (on something
>>>> else right now, I can try, but no promises).
>>>
>>> Hi Bernd,
>>>
>>> What are your thoughts on what is missing on the io-uring side for
>>> timeouts? If a request times out, it will abort the connection and
>>> AFAICT, the abort logic should already be fine for io-uring, as users
>>> can currently abort the connection through the sysfs interface and
>>> there's no internal difference in aborting through sysfs vs timeouts.
>>>
>>
>> in fuse_check_timeout() it iterates over each fud and then fpq.
>> In dev_uring.c fpq is is per queue but unrelated to fud. In current
>> fuse-io-uring fud is not cloned anymore - using fud won't work.
>> And Requests are also not queued at all on the other list
>> fuse_check_timeout() is currently checking.
>
> In the io-uring case, there still can be fuds and their associated
> fpqs given that /dev/fuse can be used still, no? So wouldn't the
> io-uring case still need this logic in fuse_check_timeout() for
> checking requests going through /dev/fuse?

Yes, these need to be additionally checked.

>
>>
>> Also, with a ring per core, maybe better to use
>> a per queue check that is core bound? I.e. zero locking overhead?
>
> How do you envision a queue check that bypasses grabbing the
> queue->lock? The timeout handler could be triggered on any core, so
> I'm not seeing how it could be core bound.

I don't want to bypass it, but maybe each queue could have its own
workq and timeout checker? And then use queue_delayed_work_on()?

>
>> And I think we can also avoid iterating over hash lists (queue->fpq),
>> but can use the 'ent_in_userspace' list.
>>
>> We need to iterate over these other entry queues anyway:
>>
>> ent_w_req_queue
>> fuse_req_bg_queue
>> ent_commit_queue
>>
>
> Why do we need to iterate through the ent lists (ent_w_req_queue and
> ent_commit_queue)? AFAICT, in io-uring a request is either on the
> fuse_req_queue/fuse_req_bg_queue or on the fpq->processing list. Even
> when an entry has been queued to ent_w_req_queue or ent_commit_queue,
> the request itself is still queued on
> fuse_req_queue/fuse_req_bg_queue/fpq->processing. I'm not sure I
> understand why we still need to look at the ent lists?

Yeah you are right, we could avoid ent_w_req_queue and ent_commit_queue
if we use fpq->processing, but processing consists of 256 lists -
overhead is much smaller by using the entry lists?

>
>>
>> And we also need to iterate over
>>
>> fuse_req_queue
>> fuse_req_bg_queue
>
> Why do we need to iterate through fuse_req_queue and
> fuse_req_bg_queue? fuse_uring_request_expired() checks the head of
> fuse_req_queue and fuse_req_bg_queue and given that requests are added
> to fuse_req_queue/fuse_req_bg_queue sequentially (eg added to the tail
> of these lists), why isn't this enough?

I admit I'm a bit lost with that question. Aren't you pointing out
the same lists as I do?

>
>
> If it's helpful, I can resubmit this patch series so that the io-uring
> changes are isolated to its own patch (eg have patch 1 and 2 from the
> original series and then have patch 3 be the io-uring changes).

Sounds good to me.

Thanks,
Bernd