Re: Fix unnecessary shared memory page allocation in CalculateShmemSize()

Hello Chao,

I'm interested and I'll look into this and get back to you.

With Regards,
Osama Abdul Qader

On Mon, 14 Sept, 2026, 12:49 pm Chao Li, <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:

> Hi,
>
> I just noticed this item when I went through my TODO list today. I
> remember finding this issue a few months ago, but at that time, only bugs
> new to PG19 were being processed, so I put it on my TODO list.
>
> This is a small issue, but it has been there for many years.
> CalculateShmemSize() has logic to round size to a multiple of a typical
> page size:
> ```
> /* might as well round it off to a multiple of a typical page size
> */
> size = add_size(size, 8192 - (size % 8192));
> ```
>
> When size is already a multiple of 8192, this add_size() call is not
> needed; it only results in an extra 8192 bytes being allocated in shared
> memory. The fix is simple:
> ```
> if (size % 8192 != 0)
> /* might as well round it off to a multiple of a typical
> page size */
> size = add_size(size, 8192 - (size % 8192));
> ```
>
> I put the comment within the if clause because I remember Tom once
> mentioning that this would be the preferred style.
>
> Best regards,
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
>
>
>
>
>