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 */