Move the shared memory size calculation to its own function

This change refactors the shared memory size calculation in
CreateSharedMemoryAndSemaphores() to its own function.  This is intended
for use in a future change related to the setup of huge pages and shared
memory with some GUCs, while useful on its own for extensions.

Author: Nathan Bossart
Discussion: https://postgr.es/m/F2772387-CE0F-46BF-B5F1-CC55516EB885@amazon.com

diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 3e4ec53a97e8d78843d4f0f8ff4cfc553acb61c0..64bc16fa8480dd8c59efc7df24012c79c8a1af3c 100644 (file)
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -75,6 +75,87 @@ RequestAddinShmemSpace(Size size)
        total_addin_request = add_size(total_addin_request, size);
 }
 
+/*
+ * CalculateShmemSize
+ *             Calculates the amount of shared memory and number of semaphores needed.
+ *
+ * If num_semaphores is not NULL, it will be set to the number of semaphores
+ * required.
+ *
+ * Note that this function freezes the additional shared memory request size
+ * from loadable modules.
+ */
+Size
+CalculateShmemSize(int *num_semaphores)
+{
+       Size            size;
+       int                     numSemas;
+
+       /* Compute number of semaphores we'll need */
+       numSemas = ProcGlobalSemas();
+       numSemas += SpinlockSemas();
+
+       /* Return the number of semaphores if requested by the caller */
+       if (num_semaphores)
+               *num_semaphores = numSemas;
+
+       /*
+        * Size of the Postgres shared-memory block is estimated via moderately-
+        * accurate estimates for the big hogs, plus 100K for the stuff that's too
+        * small to bother with estimating.
+        *
+        * We take some care to ensure that the total size request doesn't
+        * overflow size_t.  If this gets through, we don't need to be so careful
+        * during the actual allocation phase.
+        */
+       size = 100000;
+       size = add_size(size, PGSemaphoreShmemSize(numSemas));
+       size = add_size(size, SpinlockSemaSize());
+       size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
+                                                                                        sizeof(ShmemIndexEnt)));
+       size = add_size(size, dsm_estimate_size());
+       size = add_size(size, BufferShmemSize());
+       size = add_size(size, LockShmemSize());
+       size = add_size(size, PredicateLockShmemSize());
+       size = add_size(size, ProcGlobalShmemSize());
+       size = add_size(size, XLOGShmemSize());
+       size = add_size(size, CLOGShmemSize());
+       size = add_size(size, CommitTsShmemSize());
+       size = add_size(size, SUBTRANSShmemSize());
+       size = add_size(size, TwoPhaseShmemSize());
+       size = add_size(size, BackgroundWorkerShmemSize());
+       size = add_size(size, MultiXactShmemSize());
+       size = add_size(size, LWLockShmemSize());
+       size = add_size(size, ProcArrayShmemSize());
+       size = add_size(size, BackendStatusShmemSize());
+       size = add_size(size, SInvalShmemSize());
+       size = add_size(size, PMSignalShmemSize());
+       size = add_size(size, ProcSignalShmemSize());
+       size = add_size(size, CheckpointerShmemSize());
+       size = add_size(size, AutoVacuumShmemSize());
+       size = add_size(size, ReplicationSlotsShmemSize());
+       size = add_size(size, ReplicationOriginShmemSize());
+       size = add_size(size, WalSndShmemSize());
+       size = add_size(size, WalRcvShmemSize());
+       size = add_size(size, PgArchShmemSize());
+       size = add_size(size, ApplyLauncherShmemSize());
+       size = add_size(size, SnapMgrShmemSize());
+       size = add_size(size, BTreeShmemSize());
+       size = add_size(size, SyncScanShmemSize());
+       size = add_size(size, AsyncShmemSize());
+#ifdef EXEC_BACKEND
+       size = add_size(size, ShmemBackendArraySize());
+#endif
+
+       /* freeze the addin request size and include it */
+       addin_request_allowed = false;
+       size = add_size(size, total_addin_request);
+
+       /* might as well round it off to a multiple of a typical page size */
+       size = add_size(size, 8192 - (size % 8192));
+
+       return size;
+}
 
 /*
  * CreateSharedMemoryAndSemaphores
@@ -102,65 +183,8 @@ CreateSharedMemoryAndSemaphores(void)
                Size            size;
                int                     numSemas;
 
-               /* Compute number of semaphores we'll need */
-               numSemas = ProcGlobalSemas();
-               numSemas += SpinlockSemas();
-
-               /*
-                * Size of the Postgres shared-memory block is estimated via
-                * moderately-accurate estimates for the big hogs, plus 100K for the
-                * stuff that's too small to bother with estimating.
-                *
-                * We take some care during this phase to ensure that the total size
-                * request doesn't overflow size_t.  If this gets through, we don't
-                * need to be so careful during the actual allocation phase.
-                */
-               size = 100000;
-               size = add_size(size, PGSemaphoreShmemSize(numSemas));
-               size = add_size(size, SpinlockSemaSize());
-               size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
-                                                                                                sizeof(ShmemIndexEnt)));
-               size = add_size(size, dsm_estimate_size());
-               size = add_size(size, BufferShmemSize());
-               size = add_size(size, LockShmemSize());
-               size = add_size(size, PredicateLockShmemSize());
-               size = add_size(size, ProcGlobalShmemSize());
-               size = add_size(size, XLOGShmemSize());
-               size = add_size(size, CLOGShmemSize());
-               size = add_size(size, CommitTsShmemSize());
-               size = add_size(size, SUBTRANSShmemSize());
-               size = add_size(size, TwoPhaseShmemSize());
-               size = add_size(size, BackgroundWorkerShmemSize());
-               size = add_size(size, MultiXactShmemSize());
-               size = add_size(size, LWLockShmemSize());
-               size = add_size(size, ProcArrayShmemSize());
-               size = add_size(size, BackendStatusShmemSize());
-               size = add_size(size, SInvalShmemSize());
-               size = add_size(size, PMSignalShmemSize());
-               size = add_size(size, ProcSignalShmemSize());
-               size = add_size(size, CheckpointerShmemSize());
-               size = add_size(size, AutoVacuumShmemSize());
-               size = add_size(size, ReplicationSlotsShmemSize());
-               size = add_size(size, ReplicationOriginShmemSize());
-               size = add_size(size, WalSndShmemSize());
-               size = add_size(size, WalRcvShmemSize());
-               size = add_size(size, PgArchShmemSize());
-               size = add_size(size, ApplyLauncherShmemSize());
-               size = add_size(size, SnapMgrShmemSize());
-               size = add_size(size, BTreeShmemSize());
-               size = add_size(size, SyncScanShmemSize());
-               size = add_size(size, AsyncShmemSize());
-#ifdef EXEC_BACKEND
-               size = add_size(size, ShmemBackendArraySize());
-#endif
-
-               /* freeze the addin request size and include it */
-               addin_request_allowed = false;
-               size = add_size(size, total_addin_request);
-
-               /* might as well round it off to a multiple of a typical page size */
-               size = add_size(size, 8192 - (size % 8192));
-
+               /* Compute the size of the shared-memory block */
+               size = CalculateShmemSize(&numSemas);
                elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
 
                /*

diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 753a6dd4d7e9773425718791d2e1dad8165d9338..80e191d407db97b6f26a3a363b519cf5c1092551 100644 (file)
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -77,6 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
 /* ipci.c */
 extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
 
+extern Size CalculateShmemSize(int *num_semaphores);
 extern void CreateSharedMemoryAndSemaphores(void);
 
 #endif                                                 /* IPC_H */