Date: Wed, 1 Sep 2021 15:53:52 +0900
From: Michael Paquier <michael@paquier.xyz>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	Andres Freund <andres@anarazel.de>,
	Magnus Hagander <magnus@hagander.net>,
	Mark Dilger <mark.dilger@enterprisedb.com>,
	Don Seiler <don@seiler.us>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Estimating HugePages Requirements?
Message-ID: <YS8jgN37QvlrKnzQ@paquier.xyz>
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On Tue, Aug 31, 2021 at 05:37:52AM +0000, Bossart, Nathan wrote:
> I moved the GUC calculation to ipci.c, adjusted the docs, and added a
> huge_pages_required GUC.  It's still a little rough around the edges,
> and I haven't tested it on Windows, but this seems like the direction
> the patch is headed.

Hmm.  I am not sure about the addition of huge_pages_required, knowing
that we would have shared_memory_size.  I'd rather let the calculation
part to the user with a scan of /proc/meminfo.

+#elif defined(WIN32)
+   hp_size = GetLargePageMinimum();
+#endif
+
+#if defined(MAP_HUGETLB) || defined(WIN32)
+   hp_required = (size_b / hp_size) + 1;
As of [1], there is the following description:
"If the processor does not support large pages, the return value is
zero."
So there is a problem here.

[1]: https://docs.microsoft.com/en-us/windows/win32/api/memoryapi/nf-memoryapi-getlargepageminimum
--
Michael

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