Remove the extra memory context with own arena for sending

The changes in this MR prevent the memory used for sending the outgoing
TCP requests to spike so much.  That strictly remove the extra need for
own memory context, and thus since we generally prefer simplicity,
remove the extra memory context with own jemalloc arenas just for the
outgoing send buffers.

lib/ns/client.c

@@ -387,7 +387,7 @@ client_put_tcp_buffer(ns_client_t *client) {
 	}
 
 	if (client->tcpbuf != client->manager->tcp_buffer) {
-		isc_mem_put(client->manager->send_mctx, client->tcpbuf,
+		isc_mem_put(client->manager->mctx, client->tcpbuf,
 			    client->tcpbuf_size);
 	}
 
@@ -452,7 +452,7 @@ client_sendpkg(ns_client_t *client, isc_buffer_t *buffer) {
 			 * correct size and freeing the big buffer.
 			 */
 			unsigned char *new_tcpbuf =
-				isc_mem_get(client->manager->send_mctx, used);
+				isc_mem_get(client->manager->mctx, used);
 			memmove(new_tcpbuf, buffer->base, used);
 
 			/*
@@ -2498,8 +2498,6 @@ clientmgr_destroy_cb(void *arg) {
 
 	dns_message_destroypools(&manager->rdspool, &manager->namepool);
 
-	isc_mem_detach(&manager->send_mctx);
-
 	isc_mem_putanddetach(&manager->mctx, manager, sizeof(*manager));
 }
 
@@ -2534,61 +2532,6 @@ ns_clientmgr_create(ns_server_t *sctx, isc_loopmgr_t *loopmgr,
 
 	dns_message_createpools(mctx, &manager->namepool, &manager->rdspool);
 
-	/*
-	 * We create specialised per-worker memory context specifically
-	 * dedicated and tuned for allocating send buffers as it is a very
-	 * common operation. Not doing so may result in excessive memory
-	 * use in certain workloads.
-	 *
-	 * Please see this thread for more details:
-	 *
-	 * https://github.com/jemalloc/jemalloc/issues/2483
-	 *
-	 * In particular, this information from the jemalloc developers is
-	 * of the most interest:
-	 *
-	 * https://github.com/jemalloc/jemalloc/issues/2483#issuecomment-1639019699
-	 * https://github.com/jemalloc/jemalloc/issues/2483#issuecomment-1698173849
-	 *
-	 * In essence, we use the following memory management strategy:
-	 *
-	 * 1. We use a per-worker memory arena for send buffers memory
-	 * allocation to reduce lock contention (In reality, we create a
-	 * per-client manager arena, but we have one client manager per
-	 * worker).
-	 *
-	 * 2. The automatically created arenas settings remain unchanged
-	 * and may be controlled by users (e.g. by setting the
-	 * "MALLOC_CONF" variable).
-	 *
-	 * 3. We attune the arenas to not use dirty pages cache as the
-	 * cache would have a poor reuse rate, and that is known to
-	 * significantly contribute to excessive memory use.
-	 *
-	 * 4. There is no strict need for the dirty cache, as there is a
-	 * per arena bin for each allocation size, so because we initially
-	 * allocate strictly 64K per send buffer (enough for a DNS
-	 * message), allocations would get directed to one bin (an "object
-	 * pool" or a "slab") maintained within an arena. That is, there
-	 * is an object pool already, specifically to optimise for the
-	 * case of frequent allocations of objects of the given size. The
-	 * object pool should suffice our needs, as we will end up
-	 * recycling the objects from there without the need to back it by
-	 * an additional layer of dirty pages cache. The dirty pages cache
-	 * would have worked better in the case when there are more
-	 * allocation bins involved due to a higher reuse rate (the case
-	 * of a more "generic" memory management).
-	 */
-	isc_mem_create_arena(&manager->send_mctx);
-	isc_mem_setname(manager->send_mctx, "sendbufs");
-	(void)isc_mem_arena_set_dirty_decay_ms(manager->send_mctx, 0);
-	/*
-	 * Disable muzzy pages cache too, as versions < 5.2.0 have it
-	 * enabled by default. The muzzy pages cache goes right below the
-	 * dirty pages cache and backs it.
-	 */
-	(void)isc_mem_arena_set_muzzy_decay_ms(manager->send_mctx, 0);
-
 	manager->magic = MANAGER_MAGIC;
 
 	MTRACE("create");

lib/ns/include/ns/client.h

@@ -144,7 +144,6 @@ struct ns_clientmgr {
 	unsigned int magic;
 
 	isc_mem_t     *mctx;
-	isc_mem_t     *send_mctx;
 	isc_mempool_t *namepool;
 	isc_mempool_t *rdspool;