Date: Tue, 07 Sep 2021 15:24:21 +0900 (JST)
Message-Id: <20210907.152421.965153283301063555.horikyota.ntt@gmail.com>
To: bossartn@amazon.com
Cc: michael@paquier.xyz, pryzby@telsasoft.com, andres@anarazel.de,
 magnus@hagander.net, mark.dilger@enterprisedb.com, don@seiler.us,
 pgsql-hackers@postgresql.org
Subject: Re: Estimating HugePages Requirements?
From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
In-Reply-To: <C7F4DD29-549E-4EA3-87DA-D08D48B57B03@amazon.com>
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	<20210903.141206.103927759882272221.horikyota.ntt@gmail.com>
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At Fri, 3 Sep 2021 17:46:05 +0000, "Bossart, Nathan" <bossartn@amazon.com> wrote in 
> On 9/2/21, 10:12 PM, "Kyotaro Horiguchi" <horikyota.ntt@gmail.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