* These routines represent a fairly thin layer on top of SysV shared
* memory functionality.
*
- * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.53 2008/01/01 19:45:51 momjian Exp $
+ * src/backend/port/sysv_shmem.c
*
*-------------------------------------------------------------------------
*/
#include <signal.h>
#include <unistd.h>
#include <sys/file.h>
+#include <sys/mman.h>
#include <sys/stat.h>
#ifdef HAVE_SYS_IPC_H
#include <sys/ipc.h>
#ifdef HAVE_SYS_SHM_H
#include <sys/shm.h>
#endif
-#ifdef HAVE_KERNEL_OS_H
-#include <kernel/OS.h>
-#endif
#include "miscadmin.h"
+#include "portability/mem.h"
+#include "storage/dsm.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
+#include "utils/guc.h"
typedef key_t IpcMemoryKey; /* shared memory key passed to shmget(2) */
typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */
-#define IPCProtection (0600) /* access/modify by user only */
-
-#ifdef SHM_SHARE_MMU /* use intimate shared memory on Solaris */
-#define PG_SHMAT_FLAGS SHM_SHARE_MMU
-#else
-#define PG_SHMAT_FLAGS 0
-#endif
-
unsigned long UsedShmemSegID = 0;
void *UsedShmemSegAddr = NULL;
+static Size AnonymousShmemSize;
+static void *AnonymousShmem = NULL;
static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
static void IpcMemoryDetach(int status, Datum shmaddr);
if (shmid < 0)
{
+ int shmget_errno = errno;
+
/*
* Fail quietly if error indicates a collision with existing segment.
* One would expect EEXIST, given that we said IPC_EXCL, but perhaps
* we could get a permission violation instead? Also, EIDRM might
* occur if an old seg is slated for destruction but not gone yet.
*/
- if (errno == EEXIST || errno == EACCES
+ if (shmget_errno == EEXIST || shmget_errno == EACCES
#ifdef EIDRM
- || errno == EIDRM
+ || shmget_errno == EIDRM
#endif
)
return NULL;
/*
- * Else complain and abort
+ * Some BSD-derived kernels are known to return EINVAL, not EEXIST, if
+ * there is an existing segment but it's smaller than "size" (this is
+ * a result of poorly-thought-out ordering of error tests). To
+ * distinguish between collision and invalid size in such cases, we
+ * make a second try with size = 0. These kernels do not test size
+ * against SHMMIN in the preexisting-segment case, so we will not get
+ * EINVAL a second time if there is such a segment.
+ */
+ if (shmget_errno == EINVAL)
+ {
+ shmid = shmget(memKey, 0, IPC_CREAT | IPC_EXCL | IPCProtection);
+
+ if (shmid < 0)
+ {
+ /* As above, fail quietly if we verify a collision */
+ if (errno == EEXIST || errno == EACCES
+#ifdef EIDRM
+ || errno == EIDRM
+#endif
+ )
+ return NULL;
+ /* Otherwise, fall through to report the original error */
+ }
+ else
+ {
+ /*
+ * On most platforms we cannot get here because SHMMIN is
+ * greater than zero. However, if we do succeed in creating a
+ * zero-size segment, free it and then fall through to report
+ * the original error.
+ */
+ if (shmctl(shmid, IPC_RMID, NULL) < 0)
+ elog(LOG, "shmctl(%d, %d, 0) failed: %m",
+ (int) shmid, IPC_RMID);
+ }
+ }
+
+ /*
+ * Else complain and abort.
+ *
+ * Note: at this point EINVAL should mean that either SHMMIN or SHMMAX
+ * is violated. SHMALL violation might be reported as either ENOMEM
+ * (BSDen) or ENOSPC (Linux); the Single Unix Spec fails to say which
+ * it should be. SHMMNI violation is ENOSPC, per spec. Just plain
+ * not-enough-RAM is ENOMEM.
*/
+ errno = shmget_errno;
ereport(FATAL,
(errmsg("could not create shared memory segment: %m"),
- errdetail("Failed system call was shmget(key=%lu, size=%lu, 0%o).",
- (unsigned long) memKey, (unsigned long) size,
+ errdetail("Failed system call was shmget(key=%lu, size=%zu, 0%o).",
+ (unsigned long) memKey, size,
IPC_CREAT | IPC_EXCL | IPCProtection),
- (errno == EINVAL) ?
+ (shmget_errno == EINVAL) ?
errhint("This error usually means that PostgreSQL's request for a shared memory "
- "segment exceeded your kernel's SHMMAX parameter. You can either "
- "reduce the request size or reconfigure the kernel with larger SHMMAX. "
- "To reduce the request size (currently %lu bytes), reduce "
- "PostgreSQL's shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
- "If the request size is already small, it's possible that it is less than "
- "your kernel's SHMMIN parameter, in which case raising the request size or "
- "reconfiguring SHMMIN is called for.\n"
+ "segment exceeded your kernel's SHMMAX parameter, or possibly that "
+ "it is less than "
+ "your kernel's SHMMIN parameter.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- (unsigned long) size, NBuffers, MaxBackends) : 0,
- (errno == ENOMEM) ?
+ "memory configuration.") : 0,
+ (shmget_errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request for a shared "
- "memory segment exceeded available memory or swap space. "
- "To reduce the request size (currently %lu bytes), reduce "
- "PostgreSQL's shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
+ "memory segment exceeded your kernel's SHMALL parameter. You might need "
+ "to reconfigure the kernel with larger SHMALL.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- (unsigned long) size, NBuffers, MaxBackends) : 0,
- (errno == ENOSPC) ?
- errhint("This error does *not* mean that you have run out of disk space. "
+ "memory configuration.") : 0,
+ (shmget_errno == ENOSPC) ?
+ errhint("This error does *not* mean that you have run out of disk space. "
"It occurs either if all available shared memory IDs have been taken, "
"in which case you need to raise the SHMMNI parameter in your kernel, "
"or because the system's overall limit for shared memory has been "
- "reached. If you cannot increase the shared memory limit, "
- "reduce PostgreSQL's shared memory request (currently %lu bytes), "
- "by reducing its shared_buffers parameter (currently %d) and/or "
- "its max_connections parameter (currently %d).\n"
+ "reached.\n"
"The PostgreSQL documentation contains more information about shared "
- "memory configuration.",
- (unsigned long) size, NBuffers, MaxBackends) : 0));
+ "memory configuration.") : 0));
}
/* Register on-exit routine to delete the new segment */
/* Register on-exit routine to detach new segment before deleting */
on_shmem_exit(IpcMemoryDetach, PointerGetDatum(memAddress));
- /* Record key and ID in lockfile for data directory. */
- RecordSharedMemoryInLockFile((unsigned long) memKey,
- (unsigned long) shmid);
+ /*
+ * Store shmem key and ID in data directory lockfile. Format to try to
+ * keep it the same length always (trailing junk in the lockfile won't
+ * hurt, but might confuse humans).
+ */
+ {
+ char line[64];
+
+ sprintf(line, "%9lu %9lu",
+ (unsigned long) memKey, (unsigned long) shmid);
+ AddToDataDirLockFile(LOCK_FILE_LINE_SHMEM_KEY, line);
+ }
return memAddress;
}
static void
IpcMemoryDetach(int status, Datum shmaddr)
{
+ /* Detach System V shared memory block. */
if (shmdt(DatumGetPointer(shmaddr)) < 0)
elog(LOG, "shmdt(%p) failed: %m", DatumGetPointer(shmaddr));
+ /* Release anonymous shared memory block, if any. */
+ if (AnonymousShmem != NULL
+ && munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+ elog(LOG, "munmap(%p) failed: %m", AnonymousShmem);
}
/****************************************************************************/
* Is a previously-existing shmem segment still existing and in use?
*
* The point of this exercise is to detect the case where a prior postmaster
- * crashed, but it left child backends that are still running. Therefore
+ * crashed, but it left child backends that are still running. Therefore
* we only care about shmem segments that are associated with the intended
* DataDir. This is an important consideration since accidental matches of
* shmem segment IDs are reasonably common.
return true;
}
+/*
+ * Creates an anonymous mmap()ed shared memory segment.
+ *
+ * Pass the requested size in *size. This function will modify *size to the
+ * actual size of the allocation, if it ends up allocating a segment that is
+ * larger than requested.
+ */
+#ifndef EXEC_BACKEND
+static void *
+CreateAnonymousSegment(Size *size)
+{
+ Size allocsize = *size;
+ void *ptr = MAP_FAILED;
+ int mmap_errno = 0;
+
+#ifndef MAP_HUGETLB
+ if (huge_pages == HUGE_PAGES_ON)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("huge TLB pages not supported on this platform")));
+#else
+ if (huge_pages == HUGE_PAGES_ON || huge_pages == HUGE_PAGES_TRY)
+ {
+ /*
+ * Round up the request size to a suitable large value.
+ *
+ * Some Linux kernel versions are known to have a bug, which causes
+ * mmap() with MAP_HUGETLB to fail if the request size is not a
+ * multiple of any supported huge page size. To work around that, we
+ * round up the request size to nearest 2MB. 2MB is the most common
+ * huge page page size on affected systems.
+ *
+ * Aside from that bug, even with a kernel that does the allocation
+ * correctly, rounding it up ourselves avoids wasting memory. Without
+ * it, if we for example make an allocation of 2MB + 1 bytes, the
+ * kernel might decide to use two 2MB huge pages for that, and waste 2
+ * MB - 1 of memory. When we do the rounding ourselves, we can use
+ * that space for allocations.
+ */
+ int hugepagesize = 2 * 1024 * 1024;
+
+ if (allocsize % hugepagesize != 0)
+ allocsize += hugepagesize - (allocsize % hugepagesize);
+
+ ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+ PG_MMAP_FLAGS | MAP_HUGETLB, -1, 0);
+ mmap_errno = errno;
+ if (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED)
+ elog(DEBUG1, "mmap with MAP_HUGETLB failed, huge pages disabled: %m");
+ }
+#endif
+
+ if (huge_pages == HUGE_PAGES_OFF ||
+ (huge_pages == HUGE_PAGES_TRY && ptr == MAP_FAILED))
+ {
+ /*
+ * use the original size, not the rounded up value, when falling back
+ * to non-huge pages.
+ */
+ allocsize = *size;
+ ptr = mmap(NULL, allocsize, PROT_READ | PROT_WRITE,
+ PG_MMAP_FLAGS, -1, 0);
+ mmap_errno = errno;
+ }
+
+ if (ptr == MAP_FAILED)
+ {
+ errno = mmap_errno;
+ ereport(FATAL,
+ (errmsg("could not map anonymous shared memory: %m"),
+ (mmap_errno == ENOMEM) ?
+ errhint("This error usually means that PostgreSQL's request "
+ "for a shared memory segment exceeded available memory, "
+ "swap space or huge pages. To reduce the request size "
+ "(currently %zu bytes), reduce PostgreSQL's shared "
+ "memory usage, perhaps by reducing shared_buffers or "
+ "max_connections.",
+ *size) : 0));
+ }
+
+ *size = allocsize;
+ return ptr;
+}
+#endif
/*
* PGSharedMemoryCreate
* the storage.
*
* Dead Postgres segments are recycled if found, but we do not fail upon
- * collision with non-Postgres shmem segments. The idea here is to detect and
+ * collision with non-Postgres shmem segments. The idea here is to detect and
* re-use keys that may have been assigned by a crashed postmaster or backend.
*
* makePrivate means to always create a new segment, rather than attach to
* or recycle any existing segment.
*
* The port number is passed for possible use as a key (for SysV, we use
- * it to generate the starting shmem key). In a standalone backend,
+ * it to generate the starting shmem key). In a standalone backend,
* zero will be passed.
*/
PGShmemHeader *
-PGSharedMemoryCreate(Size size, bool makePrivate, int port)
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
+ PGShmemHeader **shim)
{
IpcMemoryKey NextShmemSegID;
void *memAddress;
PGShmemHeader *hdr;
IpcMemoryId shmid;
struct stat statbuf;
+ Size sysvsize;
+
+#if defined(EXEC_BACKEND) || !defined(MAP_HUGETLB)
+ if (huge_pages == HUGE_PAGES_ON)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("huge pages not supported on this platform")));
+#endif
/* Room for a header? */
Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
+ /*
+ * As of PostgreSQL 9.3, we normally allocate only a very small amount of
+ * System V shared memory, and only for the purposes of providing an
+ * interlock to protect the data directory. The real shared memory block
+ * is allocated using mmap(). This works around the problem that many
+ * systems have very low limits on the amount of System V shared memory
+ * that can be allocated. Even a limit of a few megabytes will be enough
+ * to run many copies of PostgreSQL without needing to adjust system
+ * settings.
+ *
+ * We assume that no one will attempt to run PostgreSQL 9.3 or later on
+ * systems that are ancient enough that anonymous shared memory is not
+ * supported, such as pre-2.4 versions of Linux. If that turns out to be
+ * false, we might need to add a run-time test here and do this only if
+ * the running kernel supports it.
+ *
+ * However, we disable this logic in the EXEC_BACKEND case, and fall back
+ * to the old method of allocating the entire segment using System V
+ * shared memory, because there's no way to attach an mmap'd segment to a
+ * process after exec(). Since EXEC_BACKEND is intended only for
+ * developer use, this shouldn't be a big problem.
+ */
+#ifndef EXEC_BACKEND
+ AnonymousShmem = CreateAnonymousSegment(&size);
+ AnonymousShmemSize = size;
+
+ /* Now we need only allocate a minimal-sized SysV shmem block. */
+ sysvsize = sizeof(PGShmemHeader);
+#else
+ sysvsize = size;
+#endif
+
/* Make sure PGSharedMemoryAttach doesn't fail without need */
UsedShmemSegAddr = NULL;
for (NextShmemSegID++;; NextShmemSegID++)
{
/* Try to create new segment */
- memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
+ memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
if (memAddress)
break; /* successful create and attach */
/*
* The segment appears to be from a dead Postgres process, or from a
- * previous cycle of life in this same process. Zap it, if possible.
- * This probably shouldn't fail, but if it does, assume the segment
- * belongs to someone else after all, and continue quietly.
+ * previous cycle of life in this same process. Zap it, if possible,
+ * and any associated dynamic shared memory segments, as well. This
+ * probably shouldn't fail, but if it does, assume the segment belongs
+ * to someone else after all, and continue quietly.
*/
+ if (hdr->dsm_control != 0)
+ dsm_cleanup_using_control_segment(hdr->dsm_control);
shmdt(memAddress);
if (shmctl(shmid, IPC_RMID, NULL) < 0)
continue;
/*
* Now try again to create the segment.
*/
- memAddress = InternalIpcMemoryCreate(NextShmemSegID, size);
+ memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
if (memAddress)
break; /* successful create and attach */
hdr = (PGShmemHeader *) memAddress;
hdr->creatorPID = getpid();
hdr->magic = PGShmemMagic;
+ hdr->dsm_control = 0;
/* Fill in the data directory ID info, too */
if (stat(DataDir, &statbuf) < 0)
*/
hdr->totalsize = size;
hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
+ *shim = hdr;
/* Save info for possible future use */
UsedShmemSegAddr = memAddress;
UsedShmemSegID = (unsigned long) NextShmemSegID;
- return hdr;
+ /*
+ * If AnonymousShmem is NULL here, then we're not using anonymous shared
+ * memory, and should return a pointer to the System V shared memory
+ * block. Otherwise, the System V shared memory block is only a shim, and
+ * we must return a pointer to the real block.
+ */
+ if (AnonymousShmem == NULL)
+ return hdr;
+ memcpy(AnonymousShmem, hdr, sizeof(PGShmemHeader));
+ return (PGShmemHeader *) AnonymousShmem;
}
#ifdef EXEC_BACKEND
/*
* PGSharedMemoryReAttach
*
- * Re-attach to an already existing shared memory segment. In the non
+ * Re-attach to an already existing shared memory segment. In the non
* EXEC_BACKEND case this is not used, because postmaster children inherit
* the shared memory segment attachment via fork().
*
if (hdr != origUsedShmemSegAddr)
elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
hdr, origUsedShmemSegAddr);
+ dsm_set_control_handle(((PGShmemHeader *) hdr)->dsm_control);
UsedShmemSegAddr = hdr; /* probably redundant */
}
*
* Detach from the shared memory segment, if still attached. This is not
* intended for use by the process that originally created the segment
- * (it will have an on_shmem_exit callback registered to do that). Rather,
+ * (it will have an on_shmem_exit callback registered to do that). Rather,
* this is for subprocesses that have inherited an attachment and want to
* get rid of it.
*/
elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
UsedShmemSegAddr = NULL;
}
+
+ /* Release anonymous shared memory block, if any. */
+ if (AnonymousShmem != NULL
+ && munmap(AnonymousShmem, AnonymousShmemSize) < 0)
+ elog(LOG, "munmap(%p) failed: %m", AnonymousShmem);
}
projects / postgresql / blobdiff