Обсуждение: AioCtl Shared Memory size fix

On Mon, 15 Sept 2025 at 13:33, Madhukar . <madhukarprasad@google.com> wrote:
>
> Hi Folks,
>
> While reviewing AIO code, we found an issue with AioCtlShmemSize function. The function was not accounting for
io_handleswhich is used post shared memory alloc in AioShmemInit.
 

Good catch.

Presumably this was `PgAioHandle io_handles[]` at some point, but now
that it's a pointer it's a proper part of the struct's own size, and
should be treated as such for memory accounting.

> Please find a patch to account for io_handles member of PgAioCtl.
> The patch uses sizeof(PgAioCtl) instead of offsetof(PgAioCtl, io_handles) in AioCtlShmemSize.

LGTM.


Kind regards,

Matthias van de Meent
Databricks

On Mon, Sep 15, 2025 at 02:06:03PM +0200, Matthias van de Meent wrote:
> Presumably this was `PgAioHandle io_handles[]` at some point, but now
> that it's a pointer it's a proper part of the struct's own size, and
> should be treated as such for memory accounting.

I would bet on a FLEXIBLE_ARRAY_MEMBER from a previous version..

>> Please find a patch to account for io_handles member of PgAioCtl.
>> The patch uses sizeof(PgAioCtl) instead of offsetof(PgAioCtl, io_handles) in AioCtlShmemSize.
>
> LGTM.

Yep, will fix.  Thanks for the report, the patch and the review, to
both of you.
--
Michael

Hi,

On 2025-09-16 15:50:20 +0900, Michael Paquier wrote:
> On Mon, Sep 15, 2025 at 02:06:03PM +0200, Matthias van de Meent wrote:
> > Presumably this was `PgAioHandle io_handles[]` at some point, but now
> > that it's a pointer it's a proper part of the struct's own size, and
> > should be treated as such for memory accounting.
> 
> I would bet on a FLEXIBLE_ARRAY_MEMBER from a previous version..

Indeed. I don't remember for sure why I changed it, but I think it may have
been to make the different allocations more visible in pg_shmem_allocations.


> >> Please find a patch to account for io_handles member of PgAioCtl.
> >> The patch uses sizeof(PgAioCtl) instead of offsetof(PgAioCtl, io_handles) in AioCtlShmemSize.
> > 
> > LGTM.
> 
> Yep, will fix.  Thanks for the report, the patch and the review, to
> both of you.

Thanks for finding and fixing!

Greetings,

Andres Freund