Horton

Re: Estimating HugePages Requirements?

Michael Paquier <michael@paquier.xyz>

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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>
Date: 2021-09-01T06:53:52Z
Lists: pgsql-hackers 
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

Commits

  1. Silence extra logging when using "postgres -C" on runtime-computed GUCs

  2. doc: Improve postgres command for shared_memory_size_in_huge_pages

  3. Introduce GUC shared_memory_size_in_huge_pages

  4. Support "postgres -C" with runtime-computed GUCs

  5. Make shared_memory_size a preset option

  6. Introduce GUC shared_memory_size

  7. Move the shared memory size calculation to its own function

  8. Add new GUC, max_worker_processes, limiting number of bgworkers.