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Add GUC parameter "huge_pages_status"
This is useful to show the allocation state of huge pages when setting up a server with "huge_pages = try", where allocating huge pages would be attempted but the server would continue its startup sequence even if the allocation fails. The effective status of huge pages is not easily visible without OS-level tools (or for instance, a lookup at /proc/N/smaps), and the environments where Postgres runs may not authorize that. Like the other GUCs related to huge pages, this works for Linux and Windows. This GUC can report as values: - "on", if huge pages were allocated. - "off", if huge pages were not allocated. - "unknown", a special state that could only be seen when using for example postgres -C because it is only possible to know if the shared memory allocation worked after we can check for the GUC values, even if checking a runtime-computed GUC. This value should never be seen when querying for the GUC on a running server. An assertion is added to check that. The discussion has also turned around having a new function to grab this status, but this would have required more tricks for -DEXEC_BACKEND, something that GUCs already handle. Noriyoshi Shinoda has initiated the thread that has led to the result of this commit. Author: Justin Pryzby Reviewed-by: Nathan Bossart, Kyotaro Horiguchi, Michael Paquier Discussion: https://postgr.es/m/TU4PR8401MB1152EBB0D271F827E2E37A01EECC9@TU4PR8401MB1152.NAMPRD84.PROD.OUTLOOK.COM
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‎doc/src/sgml/config.sgml

Lines changed: 22 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1727,7 +1727,9 @@ include_dir 'conf.d'
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server will try to request huge pages, but fall back to the default if
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that fails. With <literal>on</literal>, failure to request huge pages
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will prevent the server from starting up. With <literal>off</literal>,
1730-
huge pages will not be requested.
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huge pages will not be requested. The actual state of huge pages is
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indicated by the server variable
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<xref linkend="guc-huge-pages-status"/>.
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</para>
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<para>
@@ -10738,6 +10740,25 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
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</listitem>
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</varlistentry>
1074010742

10743+
<varlistentry id="guc-huge-pages-status" xreflabel="huge_pages_status">
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<term><varname>huge_pages_status</varname> (<type>enum</type>)
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<indexterm>
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<primary><varname>huge_pages_status</varname> configuration parameter</primary>
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</indexterm>
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</term>
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<listitem>
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<para>
10751+
Reports the state of huge pages in the current instance:
10752+
<literal>on</literal>, <literal>off</literal>, or
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<literal>unknown</literal> (if displayed with
10754+
<literal>postgres -C</literal>).
10755+
This parameter is useful to determine whether allocation of huge pages
10756+
was successful under <literal>huge_pages=try</literal>.
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See <xref linkend="guc-huge-pages"/> for more information.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="guc-integer-datetimes" xreflabel="integer_datetimes">
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<term><varname>integer_datetimes</varname> (<type>boolean</type>)
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<indexterm>

‎src/backend/port/sysv_shmem.c

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -627,6 +627,14 @@ CreateAnonymousSegment(Size *size)
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}
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#endif
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630+
/*
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* Report whether huge pages are in use. This needs to be tracked before
632+
* the second mmap() call if attempting to use huge pages failed
633+
* previously.
634+
*/
635+
SetConfigOption("huge_pages_status", (ptr == MAP_FAILED) ? "off" : "on",
636+
PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
637+
630638
if (ptr == MAP_FAILED && huge_pages != HUGE_PAGES_ON)
631639
{
632640
/*
@@ -737,8 +745,14 @@ PGSharedMemoryCreate(Size size,
737745
sysvsize = sizeof(PGShmemHeader);
738746
}
739747
else
748+
{
740749
sysvsize = size;
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751+
/* huge pages are only available with mmap */
752+
SetConfigOption("huge_pages_status", "off",
753+
PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
754+
}
755+
742756
/*
743757
* Loop till we find a free IPC key. Trust CreateDataDirLockFile() to
744758
* ensure no more than one postmaster per data directory can enter this

‎src/backend/port/win32_shmem.c

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -401,6 +401,11 @@ PGSharedMemoryCreate(Size size,
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on_shmem_exit(pgwin32_SharedMemoryDelete, PointerGetDatum(hmap2));
402402

403403
*shim = hdr;
404+
405+
/* Report whether huge pages are in use */
406+
SetConfigOption("huge_pages_status", (flProtect & SEC_LARGE_PAGES) ?
407+
"on" : "off", PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
408+
404409
return hdr;
405410
}
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‎src/backend/storage/ipc/ipci.c

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -190,6 +190,13 @@ CreateSharedMemoryAndSemaphores(void)
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*/
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seghdr = PGSharedMemoryCreate(size, &shim);
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193+
/*
194+
* Make sure that huge pages are never reported as "unknown" while the
195+
* server is running.
196+
*/
197+
Assert(strcmp("unknown",
198+
GetConfigOption("huge_pages_status", false, false)) != 0);
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193200
InitShmemAccess(seghdr);
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/*

‎src/backend/utils/misc/guc_tables.c

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -365,6 +365,13 @@ static const struct config_enum_entry huge_pages_options[] = {
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{NULL, 0, false}
366366
};
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368+
static const struct config_enum_entry huge_pages_status_options[] = {
369+
{"off", HUGE_PAGES_OFF, false},
370+
{"on", HUGE_PAGES_ON, false},
371+
{"unknown", HUGE_PAGES_UNKNOWN, false},
372+
{NULL, 0, false}
373+
};
374+
368375
static const struct config_enum_entry recovery_prefetch_options[] = {
369376
{"off", RECOVERY_PREFETCH_OFF, false},
370377
{"on", RECOVERY_PREFETCH_ON, false},
@@ -550,6 +557,7 @@ int ssl_renegotiation_limit;
550557
*/
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int huge_pages = HUGE_PAGES_TRY;
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int huge_page_size;
560+
int huge_pages_status = HUGE_PAGES_UNKNOWN;
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/*
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* These variables are all dummies that don't do anything, except in some
@@ -4876,6 +4884,17 @@ struct config_enum ConfigureNamesEnum[] =
48764884
NULL, NULL, NULL
48774885
},
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4887+
{
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{"huge_pages_status", PGC_INTERNAL, PRESET_OPTIONS,
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gettext_noop("Indicates the status of huge pages."),
4890+
NULL,
4891+
GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
4892+
},
4893+
&huge_pages_status,
4894+
HUGE_PAGES_UNKNOWN, huge_pages_status_options,
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NULL, NULL, NULL
4896+
},
4897+
48794898
{
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{"recovery_prefetch", PGC_SIGHUP, WAL_RECOVERY,
48814900
gettext_noop("Prefetch referenced blocks during recovery."),

‎src/include/storage/pg_shmem.h

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -46,12 +46,13 @@ extern PGDLLIMPORT int shared_memory_type;
4646
extern PGDLLIMPORT int huge_pages;
4747
extern PGDLLIMPORT int huge_page_size;
4848

49-
/* Possible values for huge_pages */
49+
/* Possible values for huge_pages and huge_pages_status */
5050
typedef enum
5151
{
5252
HUGE_PAGES_OFF,
5353
HUGE_PAGES_ON,
54-
HUGE_PAGES_TRY
54+
HUGE_PAGES_TRY, /* only for huge_pages */
55+
HUGE_PAGES_UNKNOWN /* only for huge_pages_status */
5556
} HugePagesType;
5657

5758
/* Possible values for shared_memory_type */

‎src/test/authentication/t/003_peer.pl

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -100,6 +100,12 @@ sub test_role
100100
$node->safe_psql('postgres',
101101
q(select (string_to_array(SYSTEM_USER, ':'))[2]));
102102

103+
# While on it, check the status of huge pages, that can be either on
104+
# or off, but never unknown.
105+
my $huge_pages_status =
106+
$node->safe_psql('postgres', q(SHOW huge_pages_status;));
107+
isnt($huge_pages_status, 'unknown', "check huge_pages_status");
108+
103109
# Tests without the user name map.
104110
# Failure as connection is attempted with a database role not mapping
105111
# to an authorized system user.

‎src/test/authentication/t/005_sspi.pl

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,10 @@
2121
$node->append_conf('postgresql.conf', "log_connections = on\n");
2222
$node->start;
2323

24+
my $huge_pages_status =
25+
$node->safe_psql('postgres', q(SHOW huge_pages_status;));
26+
isnt($huge_pages_status, 'unknown', "check huge_pages_status");
27+
2428
# SSPI is set up by default. Make sure it interacts correctly with
2529
# require_auth.
2630
$node->connect_ok("require_auth=sspi",

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