On Mon, Sep 27, 2021 at 9:04 PM PG Doc comments form <nore...@postgresql.org> wrote: > The following documentation comment has been logged on the website: > > Page: https://www.postgresql.org/docs/13/kernel-resources.html > Description: > > It seems that the huge_pages parameter is ignored when shared_memory_type is > sysv. The server successfully starts with huge_pages=on, but actually > doesn't use huge pages (relying on /proc/meminfo). I think that this is > worth mentioning in the "Linux Huge Pages" section.
Yeah. The thread that added shared_memory_type=sysv had an unfinished follow-up patch that stalled[1]. The goal of that patch was to add huge page support for shared_memory_type=sysv on AIX, and it is still waiting for testing and polishing by an AIX-enabled hacker. That second patch included exactly such a documentation adjustment, and an error message too (the idea was to reject that combination on Linux but allow it on AIX). Here are those bits, extracted. https://www.postgresql.org/message-id/flat/HE1PR0202MB28126DB4E0B6621CC6A1A91286D90%40HE1PR0202MB2812.eurprd02.prod.outlook.com
From c27b1eae1a528f04ab09f60de80ccfa8fbaa7534 Mon Sep 17 00:00:00 2001 From: Thomas Munro <thomas.mu...@gmail.com> Date: Fri, 22 Oct 2021 16:49:22 +1300 Subject: [PATCH] Reject huge_pages=on if shared_memory_type=sysv. It doesn't work (it could, but hasn't been implemented). Back-patch to 12, where shared_memory_type arrived. Reported-by: Alexander Lakhin <exclus...@gmail.com> Discussion: https://postgr.es/m/163271880203.22789.1125998876173795...@wrigleys.postgresql.org --- doc/src/sgml/config.sgml | 4 +++- src/backend/port/sysv_shmem.c | 6 ++++++ 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 0bcc6fd322..1c13f995a5 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1664,7 +1664,9 @@ include_dir 'conf.d' <para> At present, this setting is supported only on Linux and Windows. The setting is ignored on other systems when set to - <literal>try</literal>. + <literal>try</literal>. On Linux, it is only supported when + <varname>shared_memory_type</varname> is set to <literal>mmap</literal> + (the default). </para> <para> diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c index cd385c4df6..e7474cee59 100644 --- a/src/backend/port/sysv_shmem.c +++ b/src/backend/port/sysv_shmem.c @@ -703,6 +703,12 @@ PGSharedMemoryCreate(Size size, errmsg("huge pages not supported on this platform"))); #endif + /* For now, we don't support huge pages in SysV memory */ + if (huge_pages == HUGE_PAGES_ON && shared_memory_type != SHMEM_TYPE_MMAP) + ereport(ERROR, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("huge pages not supported with the current shared_memory_type setting"))); + /* Room for a header? */ Assert(size > MAXALIGN(sizeof(PGShmemHeader))); -- 2.30.2
