diff --git a/CHANGELOG.md b/CHANGELOG.md
index ec7581b3e..43c166dde 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,12 @@ A new flag `ACCEL_FLAG_PERSISTENT` was added to indicate the target memory is PM
 Added `bdev_nvme_add_error_injection` and `bdev_nvme_remove_error_injection` RPCs to add and
 remove NVMe error injections.
 
+### event
+
+Added `msg_mempool_size` parameter to `spdk_reactors_init` and `spdk_thread_lib_init_ext`.
+The size of `g_spdk_msg_mempool` can now be controlled through the same-named
+user option of `spdk_app_opts` structure.
+
 ### nvmf
 
 Removed deprecated max_qpairs_per_ctrlr parameter from nvmf_create_transport RPC. Use
diff --git a/examples/nvmf/nvmf/nvmf.c b/examples/nvmf/nvmf/nvmf.c
index ebd88cb32..d39259272 100644
--- a/examples/nvmf/nvmf/nvmf.c
+++ b/examples/nvmf/nvmf/nvmf.c
@@ -334,7 +334,7 @@ nvmf_init_threads(void)
 	 * framework. The size of the extra memory allocated is the second parameter.
 	 */
 	spdk_thread_lib_init_ext(nvmf_reactor_thread_op, nvmf_reactor_thread_op_supported,
-				 sizeof(struct nvmf_lw_thread));
+				 sizeof(struct nvmf_lw_thread), SPDK_DEFAULT_MSG_MEMPOOL_SIZE);
 
 	/* Spawn one system thread per CPU core. The system thread is called a reactor.
 	 * SPDK will spawn lightweight threads that must be mapped to reactors in
diff --git a/include/spdk/event.h b/include/spdk/event.h
index c98ce6a2f..444dea778 100644
--- a/include/spdk/event.h
+++ b/include/spdk/event.h
@@ -147,6 +147,13 @@ struct spdk_app_opts {
 	 * Default is `false`.
 	 */
 	bool disable_signal_handlers;
+
+	/**
+	 * The allocated size for the message pool used by the threading library.
+	 *
+	 * Default is `SPDK_DEFAULT_MSG_MEMPOOL_SIZE`.
+	 */
+	size_t msg_mempool_size;
 };
 
 /**
diff --git a/include/spdk/thread.h b/include/spdk/thread.h
index e82b35484..c260fcc7a 100644
--- a/include/spdk/thread.h
+++ b/include/spdk/thread.h
@@ -213,6 +213,9 @@ typedef void (*spdk_channel_for_each_cpl)(struct spdk_io_channel_iter *i, int st
 
 #define SPDK_IO_CHANNEL_STRUCT_SIZE	96
 
+/* Power of 2 minus 1 is optimal for memory consumption */
+#define SPDK_DEFAULT_MSG_MEMPOOL_SIZE (262144 - 1)
+
 /**
  * Initialize the threading library. Must be called once prior to allocating any threads.
  *
@@ -236,12 +239,13 @@ int spdk_thread_lib_init(spdk_new_thread_fn new_thread_fn, size_t ctx_sz);
  * \param thread_op_supported_fn Called to check whether the SPDK thread operation is supported.
  * \param ctx_sz For each thread allocated, for use by the thread scheduler. A pointer
  * to this region may be obtained by calling spdk_thread_get_ctx().
+ * \param msg_mempool_size Size of the allocated spdk_msg_mempool.
  *
  * \return 0 on success. Negated errno on failure.
  */
 int spdk_thread_lib_init_ext(spdk_thread_op_fn thread_op_fn,
 			     spdk_thread_op_supported_fn thread_op_supported_fn,
-			     size_t ctx_sz);
+			     size_t ctx_sz, size_t msg_mempool_size);
 
 /**
  * Release all resources associated with this library.
diff --git a/include/spdk_internal/event.h b/include/spdk_internal/event.h
index 1df224421..77c781e70 100644
--- a/include/spdk_internal/event.h
+++ b/include/spdk_internal/event.h
@@ -116,7 +116,7 @@ struct spdk_reactor {
 	int						resched_fd;
 } __attribute__((aligned(SPDK_CACHE_LINE_SIZE)));
 
-int spdk_reactors_init(void);
+int spdk_reactors_init(size_t msg_mempool_size);
 void spdk_reactors_fini(void);
 
 void spdk_reactors_start(void);
diff --git a/lib/event/app.c b/lib/event/app.c
index b626b1c69..c70d2d7cf 100644
--- a/lib/event/app.c
+++ b/lib/event/app.c
@@ -225,6 +225,7 @@ spdk_app_opts_init(struct spdk_app_opts *opts, size_t opts_size)
 	SET_FIELD(num_entries, SPDK_APP_DEFAULT_NUM_TRACE_ENTRIES);
 	SET_FIELD(delay_subsystem_init, false);
 	SET_FIELD(disable_signal_handlers, false);
+	SET_FIELD(msg_mempool_size, SPDK_DEFAULT_MSG_MEMPOOL_SIZE);
 #undef SET_FIELD
 }
 
@@ -520,10 +521,11 @@ app_copy_opts(struct spdk_app_opts *opts, struct spdk_app_opts *opts_user, size_
 	SET_FIELD(log);
 	SET_FIELD(base_virtaddr);
 	SET_FIELD(disable_signal_handlers);
+	SET_FIELD(msg_mempool_size);
 
 	/* You should not remove this statement, but need to update the assert statement
 	 * if you add a new field, and also add a corresponding SET_FIELD statement */
-	SPDK_STATIC_ASSERT(sizeof(struct spdk_app_opts) == 192, "Incorrect size");
+	SPDK_STATIC_ASSERT(sizeof(struct spdk_app_opts) == 200, "Incorrect size");
 
 #undef SET_FIELD
 }
@@ -600,7 +602,7 @@ spdk_app_start(struct spdk_app_opts *opts_user, spdk_msg_fn start_fn,
 	spdk_log_open(opts->log);
 	SPDK_NOTICELOG("Total cores available: %d\n", spdk_env_get_core_count());
 
-	if ((rc = spdk_reactors_init()) != 0) {
+	if ((rc = spdk_reactors_init(opts->msg_mempool_size)) != 0) {
 		SPDK_ERRLOG("Reactor Initialization failed: rc = %d\n", rc);
 		return 1;
 	}
diff --git a/lib/event/reactor.c b/lib/event/reactor.c
index 0e1b1e9a9..b3c8dea03 100644
--- a/lib/event/reactor.c
+++ b/lib/event/reactor.c
@@ -233,7 +233,7 @@ static int reactor_thread_op(struct spdk_thread *thread, enum spdk_thread_op op)
 static bool reactor_thread_op_supported(enum spdk_thread_op op);
 
 int
-spdk_reactors_init(void)
+spdk_reactors_init(size_t msg_mempool_size)
 {
 	struct spdk_reactor *reactor;
 	int rc;
@@ -274,7 +274,7 @@ spdk_reactors_init(void)
 	memset(g_reactors, 0, (g_reactor_count) * sizeof(struct spdk_reactor));
 
 	spdk_thread_lib_init_ext(reactor_thread_op, reactor_thread_op_supported,
-				 sizeof(struct spdk_lw_thread));
+				 sizeof(struct spdk_lw_thread), msg_mempool_size);
 
 	SPDK_ENV_FOREACH_CORE(i) {
 		reactor_construct(&g_reactors[i], i);
diff --git a/lib/thread/thread.c b/lib/thread/thread.c
index 841c8be52..f339591d8 100644
--- a/lib/thread/thread.c
+++ b/lib/thread/thread.c
@@ -266,19 +266,21 @@ _get_thread(void)
 }
 
 static int
-_thread_lib_init(size_t ctx_sz)
+_thread_lib_init(size_t ctx_sz, size_t msg_mempool_sz)
 {
 	char mempool_name[SPDK_MAX_MEMZONE_NAME_LEN];
 
 	g_ctx_sz = ctx_sz;
 
 	snprintf(mempool_name, sizeof(mempool_name), "msgpool_%d", getpid());
-	g_spdk_msg_mempool = spdk_mempool_create(mempool_name,
-			     262144 - 1, /* Power of 2 minus 1 is optimal for memory consumption */
+	g_spdk_msg_mempool = spdk_mempool_create(mempool_name, msg_mempool_sz,
 			     sizeof(struct spdk_msg),
 			     0, /* No cache. We do our own. */
 			     SPDK_ENV_SOCKET_ID_ANY);
 
+	SPDK_DEBUGLOG(thread, "spdk_msg_mempool was created with size: %zu\n",
+		      msg_mempool_sz);
+
 	if (!g_spdk_msg_mempool) {
 		SPDK_ERRLOG("spdk_msg_mempool creation failed\n");
 		return -1;
@@ -299,13 +301,13 @@ spdk_thread_lib_init(spdk_new_thread_fn new_thread_fn, size_t ctx_sz)
 		g_new_thread_fn = new_thread_fn;
 	}
 
-	return _thread_lib_init(ctx_sz);
+	return _thread_lib_init(ctx_sz, SPDK_DEFAULT_MSG_MEMPOOL_SIZE);
 }
 
 int
 spdk_thread_lib_init_ext(spdk_thread_op_fn thread_op_fn,
 			 spdk_thread_op_supported_fn thread_op_supported_fn,
-			 size_t ctx_sz)
+			 size_t ctx_sz, size_t msg_mempool_sz)
 {
 	assert(g_new_thread_fn == NULL);
 	assert(g_thread_op_fn == NULL);
@@ -323,7 +325,7 @@ spdk_thread_lib_init_ext(spdk_thread_op_fn thread_op_fn,
 		g_thread_op_supported_fn = thread_op_supported_fn;
 	}
 
-	return _thread_lib_init(ctx_sz);
+	return _thread_lib_init(ctx_sz, msg_mempool_sz);
 }
 
 void
diff --git a/test/unit/lib/event/app.c/app_ut.c b/test/unit/lib/event/app.c/app_ut.c
index d6485fdfa..df5ffcde1 100644
--- a/test/unit/lib/event/app.c/app_ut.c
+++ b/test/unit/lib/event/app.c/app_ut.c
@@ -56,7 +56,7 @@ DEFINE_STUB_V(spdk_subsystem_init_from_json_config, (const char *json_config_fil
 		spdk_subsystem_init_fn cb_fn, void *cb_arg, bool stop_on_error));
 DEFINE_STUB_V(spdk_reactors_start, (void));
 DEFINE_STUB_V(spdk_reactors_stop, (void *arg1));
-DEFINE_STUB(spdk_reactors_init, int, (void), 0);
+DEFINE_STUB(spdk_reactors_init, int, (size_t msg_mempool_size), 0);
 DEFINE_STUB_V(spdk_reactors_fini, (void));
 DEFINE_STUB_V(_spdk_scheduler_set_period, (uint64_t period));
 bool g_scheduling_in_progress;
diff --git a/test/unit/lib/event/reactor.c/reactor_ut.c b/test/unit/lib/event/reactor.c/reactor_ut.c
index 4089212aa..8ead75e0f 100644
--- a/test/unit/lib/event/reactor.c/reactor_ut.c
+++ b/test/unit/lib/event/reactor.c/reactor_ut.c
@@ -83,7 +83,7 @@ test_init_reactors(void)
 
 	allocate_cores(3);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	CU_ASSERT(g_reactor_state == SPDK_REACTOR_STATE_INITIALIZED);
 	for (core = 0; core < 3; core++) {
@@ -118,7 +118,7 @@ test_event_call(void)
 
 	allocate_cores(1);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	evt = spdk_event_allocate(0, ut_event_fn, &test1, &test2);
 	CU_ASSERT(evt != NULL);
@@ -155,7 +155,7 @@ test_schedule_thread(void)
 
 	allocate_cores(5);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_cpuset_set_cpu(&cpuset, 3, true);
 	g_next_core = 4;
@@ -207,7 +207,7 @@ test_reschedule_thread(void)
 
 	allocate_cores(3);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_cpuset_set_cpu(&g_reactor_core_mask, 0, true);
 	spdk_cpuset_set_cpu(&g_reactor_core_mask, 1, true);
@@ -309,7 +309,7 @@ test_for_each_reactor(void)
 
 	allocate_cores(5);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_for_each_reactor(for_each_reactor_cb, &count, &done, for_each_reactor_done);
 
@@ -404,7 +404,7 @@ test_reactor_stats(void)
 
 	allocate_cores(1);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_cpuset_set_cpu(&cpuset, 0, true);
 
@@ -577,7 +577,7 @@ test_scheduler(void)
 
 	allocate_cores(3);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_scheduler_set("dynamic");
 
@@ -816,7 +816,7 @@ test_governor(void)
 
 	allocate_cores(2);
 
-	CU_ASSERT(spdk_reactors_init() == 0);
+	CU_ASSERT(spdk_reactors_init(SPDK_DEFAULT_MSG_MEMPOOL_SIZE) == 0);
 
 	spdk_scheduler_set("dynamic");
 	spdk_governor_set("dpdk_governor");
diff --git a/test/unit/lib/thread/thread.c/thread_ut.c b/test/unit/lib/thread/thread.c/thread_ut.c
index 59728c9fa..7bb69e4ae 100644
--- a/test/unit/lib/thread/thread.c/thread_ut.c
+++ b/test/unit/lib/thread/thread.c/thread_ut.c
@@ -109,7 +109,8 @@ thread_alloc(void)
 	spdk_thread_lib_fini();
 
 	/* Scheduling callback exists with extended thread library initialization. */
-	spdk_thread_lib_init_ext(_thread_op, _thread_op_supported, 0);
+	spdk_thread_lib_init_ext(_thread_op, _thread_op_supported, 0,
+				 SPDK_DEFAULT_MSG_MEMPOOL_SIZE);
 
 	/* Scheduling succeeds */
 	g_sched_rc = 0;