Re: AIO v2.5

On Tue, Mar 18, 2025 at 9:12 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> Attached is v2.10, with the following changes:
>
> - committed core AIO infrastructure patch

Hi, yay, It's happening.jpg ;)

Some thoughts about 2.10-0004:
What do you think about putting there into (io_uring patch) info
about the need to ensure that kernel.io_uring_disabled sysctl is on ?
(some distros might shut it down) E.g. in doc/src/sgml/config.sgml
after io_method = <listitems>... there could be

--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
<literal>io_uring</literal> (execute asynchronous I/O using
io_uring, if available)
[..]
and then add something like:
+ "At present io_method=io_uring is supported only on Linux and
requires Linux's sysctl kernel.io_uring_disabled (if present) to be at
value 0 (enabled) or 1 (with kernel.io_uring_group set to PostgreSQL's
GID)."

Rationale: it seems that at least RHEL 9.x will have this knob present
(but e.g. RHEL 8.10 even kernel-ml 6.4.2 doesn't, as this seems to
come with 6.6+ but saw somewhere that somebody had issues with this on
probably backported kernel in Rocky 9.x ). Also further googling for I
have found also that mysql can throw - when executed from
podmap/docker: "mysqld: io_uring_queue_init() failed with ENOSYS:
check seccomp filters, and the kernel version (newer than 5.1
required)"

and this leaves this with two probable follow-up questions when
adjusting this sentence:
a. shouldn't we add some sentence about containers/namespaces/seccomp
allowing this ?
b. and/or shouldn't we reference in docs a minimum kernel version
(this is somewhat wild, liburing could be installed and compiled
against, but runtime kernel would be < 5.1 ?)

-J.