diff options
| -rw-r--r-- | src/backend/port/sysv_shmem.c | 89 |
1 files changed, 86 insertions, 3 deletions
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c index b28766c652e..4bbd0ec6495 100644 --- a/src/backend/port/sysv_shmem.c +++ b/src/backend/port/sysv_shmem.c @@ -19,6 +19,7 @@ #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> @@ -43,9 +44,22 @@ typedef int IpcMemoryId; /* shared memory ID returned by shmget(2) */ #define PG_SHMAT_FLAGS 0 #endif +/* Linux prefers MAP_ANONYMOUS, but the flag is called MAP_ANON on other systems. */ +#ifndef MAP_ANONYMOUS +#define MAP_ANONYMOUS MAP_ANON +#endif + +/* BSD-derived systems have MAP_HASSEMAPHORE, but it's not present (or needed) on Linux. */ +#ifndef MAP_HASSEMAPHORE +#define MAP_HASSEMAPHORE 0 +#endif + +#define PG_MMAP_FLAGS (MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE) unsigned long UsedShmemSegID = 0; void *UsedShmemSegAddr = NULL; +static Size AnonymousShmemSize; +static PGShmemHeader *AnonymousShmem; static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size); static void IpcMemoryDetach(int status, Datum shmaddr); @@ -218,8 +232,13 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size) 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); } /****************************************************************************/ @@ -357,10 +376,59 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port) PGShmemHeader *hdr; IpcMemoryId shmid; struct stat statbuf; + Size allocsize = size; /* 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. + * + * 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 + { + long pagesize = sysconf(_SC_PAGE_SIZE); + + /* + * pagesize will, for practical purposes, always be a power of two. + * But just in case it isn't, we do it this way instead of using + * TYPEALIGN(). + */ + AnonymousShmemSize = size; + if (size % pagesize != 0) + AnonymousShmemSize += pagesize - (size % pagesize); + + /* + * 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. + */ + AnonymousShmem = mmap(NULL, size, PROT_READ|PROT_WRITE, PG_MMAP_FLAGS, + -1, 0); + if (AnonymousShmem == NULL) + ereport(FATAL, + (errmsg("could not map %lu bytes of anonymous shared memory: %m", + (unsigned long) AnonymousShmemSize))); + + /* Now we can allocate a minimal SHM block. */ + allocsize = sizeof(PGShmemHeader); + } +#endif + /* Make sure PGSharedMemoryAttach doesn't fail without need */ UsedShmemSegAddr = NULL; @@ -370,7 +438,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port) for (NextShmemSegID++;; NextShmemSegID++) { /* Try to create new segment */ - memAddress = InternalIpcMemoryCreate(NextShmemSegID, size); + memAddress = InternalIpcMemoryCreate(NextShmemSegID, allocsize); if (memAddress) break; /* successful create and attach */ @@ -409,7 +477,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port) /* * Now try again to create the segment. */ - memAddress = InternalIpcMemoryCreate(NextShmemSegID, size); + memAddress = InternalIpcMemoryCreate(NextShmemSegID, allocsize); if (memAddress) break; /* successful create and attach */ @@ -448,7 +516,17 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port) 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 AnonymousShmem; + } #ifdef EXEC_BACKEND @@ -516,6 +594,11 @@ PGSharedMemoryDetach(void) 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); } |