Re: AIO v2.5

Hi,

On 2025-03-25 12:39:56 -0700, Noah Misch wrote:
> On Tue, Mar 25, 2025 at 02:58:37PM -0400, Andres Freund wrote:
> > I don't know if that's an intentional or unintentional behavioral difference.
> >
> > There are 2 1/2 ways around this:
> >
> > 1) Stop using IOSQE_ASYNC heuristic
> > 2a) Wait for all in-flight IOs when any FD gets closed
> > 2b) Wait for all in-flight IOs using FD when it gets closed
> >
> > Given that we have clear evidence that io_uring doesn't completely support
> > closing FDs while IOs are in flight, be it a bug or intentional, it seems
> > clearly better to go for 2a or 2b.
>
> Agreed. If a workload spends significant time on fd.c closing files, I
> suspect that workload already won't have impressive benchmark numbers.
> Performance-seeking workloads will already want to tune FD usage high enough
> to keep FDs long-lived. So (1) clearly loses, and neither (2a) nor (2b)
> clearly beats the other. I'd try (2b) first but, if complicated, quickly
> abandon it in favor of (2a). What other considerations could be important?

The only other consideration I can think of is whether this should happen for
all io_methods or not.

I'm inclined to do it via a bool in IoMethodOps, but I guess one could argue
it's a bit weird to have a bool in a struct called *Ops.

Greetings,

Andres Freund