diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index c392d4f..ece9674 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -48,6 +48,11 @@ shmem_startup_hook_type shmem_startup_hook = NULL;
 static Size total_addin_request = 0;
 static bool addin_request_allowed = true;
 
+/*
+ * Signals whether shared memory is currently being initialized, while the
+ * postmaster hasn't forked any children yet.
+ */
+bool ShmemInitInProgress = false;
 
 /*
  * RequestAddinShmemSpace
@@ -97,6 +102,12 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		int			numSemas;
 
 		/*
+		 * We're now initializing shared memory, and we won't have forked
+		 * children yet.
+		 */
+		ShmemInitInProgress = true;
+
+		/*
 		 * 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.
@@ -261,4 +272,7 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 	 */
 	if (shmem_startup_hook)
 		shmem_startup_hook();
+
+	if(!IsUnderPostmaster)
+		ShmemInitInProgress = false;
 }
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 82ef440..0365f9b 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -355,9 +355,11 @@ CreateLWLocks(void)
  * LWLockAssign - assign a dynamically-allocated LWLock number
  *
  * We interlock this using the same spinlock that is used to protect
- * ShmemAlloc().  Interlocking is not really necessary during postmaster
- * startup, but it is needed if any user-defined code tries to allocate
- * LWLocks after startup.
+ * ShmemAlloc().  Interlocking is not necessary while we're initializing
+ * shared memory, but it is needed for any code allocating LWLocks after
+ * startup.  Since we allocate large amounts of LWLocks for the buffer pool
+ * during startup, we avoid taking the spinlock when not needed, as it has
+ * shown to slowdown startup considerably.
  */
 LWLock *
 LWLockAssign(void)
@@ -368,14 +370,17 @@ LWLockAssign(void)
 	volatile int *LWLockCounter;
 
 	LWLockCounter = (int *) ((char *) MainLWLockArray - 3 * sizeof(int));
-	SpinLockAcquire(ShmemLock);
+	if (!ShmemInitInProgress)
+		SpinLockAcquire(ShmemLock);
 	if (LWLockCounter[0] >= LWLockCounter[1])
 	{
-		SpinLockRelease(ShmemLock);
+		if (!ShmemInitInProgress)
+			SpinLockRelease(ShmemLock);
 		elog(ERROR, "no more LWLocks available");
 	}
 	result = &MainLWLockArray[LWLockCounter[0]++].lock;
-	SpinLockRelease(ShmemLock);
+	if (!ShmemInitInProgress)
+		SpinLockRelease(ShmemLock);
 	return result;
 }
 
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 37eca7a..0f1e00a 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -63,6 +63,7 @@ typedef void (*shmem_startup_hook_type) (void);
 
 /* ipc.c */
 extern bool proc_exit_inprogress;
+extern bool ShmemInitInProgress;
 
 extern void proc_exit(int code) __attribute__((noreturn));
 extern void shmem_exit(int code);