Re: Estimating HugePages Requirements?

At Fri, 3 Sep 2021 17:46:05 +0000, "Bossart, Nathan" <bossartn(at)amazon(dot)com> wrote in
> On 9/2/21, 10:12 PM, "Kyotaro Horiguchi" <horikyota(dot)ntt(at)gmail(dot)com> wrote:
> > By the way I noticed that postgres -C huge_page_size shows 0, which I
> > think should have the number used for the calculation if we show
> > huge_page_required.
>
> I would agree with this if huge_page_size was a runtime-computed GUC,
> but since it's intended for users to explicitly request the huge page
> size, it might be slightly confusing. Perhaps another option would be
> to create a new GUC for this. Or maybe it's enough to note that the
> value will be changed from 0 at runtime if huge pages are supported.
> In any case, it might be best to handle this separately.

(Sorry, I was confused, but) yeah, agreed.

> > I noticed that postgres -C shared_memory_size showed 137 (= 144703488)
> > whereas the error message above showed 148897792 bytes (142MB). So it
> > seems that something is forgotten while calculating
> > shared_memory_size. As the consequence, launching postgres setting
> > huge_pages_required (69 pages) as vm.nr_hugepages ended up in the
> > "could not map anonymous shared memory" error.
>
> Hm. I'm not seeing this with the v5 patch set, so maybe I
> inadvertently fixed it already. Can you check this again with v5?

Thanks! I confirmed that the numbers match with v5.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center