Re: [PATCH v2] io_uring/net: use REQ_F_IMPORT_BUFFER for send_zc

[Jens Axboe]

On 3/26/25 11:23 AM, Caleb Sander Mateos wrote:
> On Wed, Mar 26, 2025 at 10:05?AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>>
>> On 3/26/25 11:01 AM, Caleb Sander Mateos wrote:
>>> On Wed, Mar 26, 2025 at 2:59?AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote:
>>>>
>>>> On 3/25/25 14:39, Caleb Sander Mateos wrote:
>>>>> Instead of a bool field in struct io_sr_msg, use REQ_F_IMPORT_BUFFER to
>>>>> track whether io_send_zc() has already imported the buffer. This flag
>>>>> already serves a similar purpose for sendmsg_zc and {read,write}v_fixed.
>>>>
>>>> It didn't apply cleanly to for-6.15/io_uring-reg-vec, but otherwise
>>>> looks good.
>>>
>>> It looks like Jens dropped my earlier patch "io_uring/net: import
>>> send_zc fixed buffer before going async":
>>> https://lore.kernel.org/io-uring/20250321184819.3847386-3-csander@xxxxxxxxxxxxxxx/T/#u
>>> .
>>> Not sure why it was dropped. But this change is independent, I can
>>> rebase it onto the current for-6.15/io_uring-reg-vec if desired.
>>
>> Mostly just around the discussion on what we want to guarantee here. I
>> do think that patch makes sense, fwiw!
> 
> I hope the approach I took for the revised NVMe passthru patch [1] is
> an acceptable compromise: the order in which io_uring issues
> operations isn't guaranteed, but userspace may opportunistically
> submit operations in parallel with a fallback path in case of failure.
> Viewed this way, I think it makes sense for the kernel to allow the
> operation using the fixed buffer to succeed even if it goes async,
> provided that it doesn't impose any burden on the io_uring
> implementation. I dropped the "Fixes" tag and added a paragraph to the
> commit message clarifying that io_uring doesn't guarantee this
> behavior, it's just an optimization.
> 
> [1]: https://lore.kernel.org/io-uring/20250324200540.910962-4-csander@xxxxxxxxxxxxxxx/T/#u

It is, I already signed off on that one, I think it's just waiting for
Keith to get queued up. Always a bit tricky during the merge window,
particularly when it ends up depending on multiple branches. But should
go in for 6.15.

When you have time, resending the net one would be useful. I do think
that one makes sense too.

-- 
Jens Axboe