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Add shared_memory_type GUC.

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Since 9.3 we have used anonymous shared mmap for our main shared memory
region, except in EXEC_BACKEND builds.  Provide a GUC so that users
can opt for System V shared memory once again, like in 9.2 and earlier.

A later patch proposes to add huge/large page support for AIX, which
requires System V shared memory and provided the motivation to revive
this possibility.  It may also be useful on some BSDs.

Author: Andres Freund (revived and documented by Thomas Munro)
Discussion: https://postgr.es/m/HE1PR0202MB28126DB4E0B6621CC6A1A91286D90%40HE1PR0202MB2812.eurprd02.prod.outlook.com
Discussion: https://postgr.es/m/2AE143D2-87D3-4AD1-AC78-CE2258230C05%40FreeBSD.org
This commit is contained in:
Thomas Munro
2019-02-03 09:55:39 +01:00
parent 0d1fe9f74e
commit f1bebef60e
7 changed files with 101 additions and 33 deletions
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42
src/backend/port/sysv_shmem.c
View File

@ -62,10 +62,11 @@
* to a process after exec(). Since EXEC_BACKEND is intended only for
* developer use, this shouldn't be a big problem. Because of this, we do
* not worry about supporting anonymous shmem in the EXEC_BACKEND cases below.
*
* As of PostgreSQL 12, we regained the ability to use a large System V shared
* memory region even in non-EXEC_BACKEND builds, if shared_memory_type is set
* to sysv (though this is not the default).
*/
#ifndef EXEC_BACKEND
#define USE_ANONYMOUS_SHMEM
#endif
typedef key_t IpcMemoryKey; /* shared memory key passed to shmget(2) */
@ -75,10 +76,8 @@ typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */
unsigned long UsedShmemSegID = 0;
void *UsedShmemSegAddr = NULL;
#ifdef USE_ANONYMOUS_SHMEM
static Size AnonymousShmemSize;
static void *AnonymousShmem = NULL;
#endif
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
@ -370,8 +369,6 @@ PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
return true;
}
#ifdef USE_ANONYMOUS_SHMEM
#ifdef MAP_HUGETLB
/*
@ -534,8 +531,6 @@ AnonymousShmemDetach(int status, Datum arg)
}
}
#endif /* USE_ANONYMOUS_SHMEM */
/*
* PGSharedMemoryCreate
*
@ -566,7 +561,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
Size sysvsize;
/* Complain if hugepages demanded but we can't possibly support them */
#if !defined(USE_ANONYMOUS_SHMEM) || !defined(MAP_HUGETLB)
#if !defined(MAP_HUGETLB)
if (huge_pages == HUGE_PAGES_ON)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@ -576,18 +571,19 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
#ifdef USE_ANONYMOUS_SHMEM
AnonymousShmem = CreateAnonymousSegment(&size);
AnonymousShmemSize = size;
if (shared_memory_type == SHMEM_TYPE_MMAP)
{
AnonymousShmem = CreateAnonymousSegment(&size);
AnonymousShmemSize = size;
/* Register on-exit routine to unmap the anonymous segment */
on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
/* Register on-exit routine to unmap the anonymous segment */
on_shmem_exit(AnonymousShmemDetach, (Datum) 0);
/* Now we need only allocate a minimal-sized SysV shmem block. */
sysvsize = sizeof(PGShmemHeader);
#else
sysvsize = size;
#endif
/* Now we need only allocate a minimal-sized SysV shmem block. */
sysvsize = sizeof(PGShmemHeader);
}
else
sysvsize = size;
/* Make sure PGSharedMemoryAttach doesn't fail without need */
UsedShmemSegAddr = NULL;
@ -687,14 +683,10 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port,
* block. Otherwise, the System V shared memory block is only a shim, and
* we must return a pointer to the real block.
*/
#ifdef USE_ANONYMOUS_SHMEM
if (AnonymousShmem == NULL)
return hdr;
memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
return (PGShmemHeader *) AnonymousShmem;
#else
return hdr;
#endif
}
#ifdef EXEC_BACKEND
@ -801,7 +793,6 @@ PGSharedMemoryDetach(void)
UsedShmemSegAddr = NULL;
}
#ifdef USE_ANONYMOUS_SHMEM
if (AnonymousShmem != NULL)
{
if (munmap(AnonymousShmem, AnonymousShmemSize) < 0)
@ -809,7 +800,6 @@ PGSharedMemoryDetach(void)
AnonymousShmem, AnonymousShmemSize);
AnonymousShmem = NULL;
}
#endif
}