Re: [PATCHSET v2 0/2] io_uring: handle short reads internally

Stefan Metzmacher
2020-08-18T07:40:51Z

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Hi Jens,

>>>> Will this be backported?
>>>
>>> I can, but not really in an efficient manner. It depends on the async
>>> buffered work to make progress, and the task_work handling retry. The
>>> latter means it's 5.7+, while the former is only in 5.9+...
>>>
>>> We can make it work for earlier kernels by just using the thread offload
>>> for that, and that may be worth doing. That would enable it in
>>> 5.7-stable and 5.8-stable. For that, you just need these two patches.
>>> Patch 1 would work as-is, while patch 2 would need a small bit of
>>> massaging since io_read() doesn't have the retry parts.
>>>
>>> I'll give it a whirl just out of curiosity, then we can debate it after
>>> that.
>>
>> Here are the two patches against latest 5.7-stable (the rc branch, as
>> we had quite a few queued up after 5.9-rc1). Totally untested, just
>> wanted to see if it was doable.
>>
>> First patch is mostly just applied, with various bits removed that we
>> don't have in 5.7. The second patch just does -EAGAIN punt for the
>> short read case, which will queue the remainder with io-wq for
>> async execution.
>>
>> Obviously needs quite a bit of testing before it can go anywhere else,
>> but wanted to throw this out there in case you were interested in
>> giving it a go...
>
> Actually passes basic testing, and doesn't return short reads. So at
> least it's not half bad, and it should be safe for you to test.
>
> I quickly looked at 5.8 as well, and the good news is that the same
> patches will apply there without changes.

Thanks, but I was just curios and I currently don't have the environment to test, sorry.

Anoop: you helped a lot reproducing the problem with 5.6, would you be able to
test the kernel patches against 5.7 or 5.8, while reverting the samba patches?
See https://lore.kernel.org/io-uring/e22220a8-669a-d302-f454-03a35c9582b4@kernel.dk/T/#t for the
whole discussion?

metze

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