Re: Draft for basic NUMA observability

On 4/7/25 18:42, Andres Freund wrote:
> ...
>>>
>>> Of course that would mean that we'd always need to
>>> pg_numa_touch_mem_if_required(), not just the first time round, because we
>>> previously might not have for a page that is now valid. But compared to the
>>> cost of actually allocating pages, the cost for that seems small.
>>
>> I suppose by "range" you mean buffers on a given memory page
>
> Correct.
>
>> and "valid" means BufferIsValid.
>
> I was thinking of checking if the BufferDesc indicates BM_VALID or
> BM_TAG_VALID.
>
> BufferIsValid() just does a range check :(.
>

Well, I guess BufferIsValid() seems a tad confusing ...

>
>> Yeah, that probably means the memory page is allocated. But if the buffer is
>> invalid, it does not mean the memory is not allocated, right? So does it
>> make the buffer not interesting?
>
> Well, you don't have contents in it it can't really affect performance. But
> yea, I agree, it's not perfect either.
>
>
>> I think we need to decide whether the current patches are good enough
>> for PG18, with the current behavior, and then maybe improve that in
>> PG19.
>
> I think as long as the docs mention this with <note> or <warning> it's ok for
> now.
>

OK, I'll add a warning explaining this.

regards

--
Tomas Vondra