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