drbd: TCP: use sk_set_memalloc and sk_allocation ATOMIC

We used to "only" set NOIO. But we are a block device, we are
in the write-out path, we may need to tap into the "reserves"
to facilitate memory reclaim.

If you expect to have serious memory pressure,
we recommend to generously increase sysctl min_free_kbytes.

drbd/drbd_transport_lb-tcp.c

@@ -1094,7 +1094,13 @@ static void dtl_setup_socket(struct dtl_transport *dtl_transport, struct socket
 	long timeout = HZ;
 
 	socket->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
-	socket->sk->sk_allocation = GFP_NOIO;
+	/* We are a block device, we are in the write-out path,
+	 * we may need memory to facilitate memory reclaim
+	 */
+	socket->sk->sk_use_task_frag = false;
+	socket->sk->sk_allocation = GFP_ATOMIC;
+	sk_set_memalloc(socket->sk);
+
 	socket->sk->sk_priority = use_for_data ? TC_PRIO_INTERACTIVE_BULK : TC_PRIO_INTERACTIVE;
 	tcp_sock_set_nodelay(socket->sk);
 

drbd/drbd_transport_tcp.c

@@ -1322,12 +1322,18 @@ static int dtt_connect(struct drbd_transport *transport)
 	dsocket->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
 	csocket->sk->sk_reuse = SK_CAN_REUSE; /* SO_REUSEADDR */
 
-	dsocket->sk->sk_allocation = GFP_NOIO;
-	csocket->sk->sk_allocation = GFP_NOIO;
+	/* We are a block device, we are in the write-out path,
+	 * we may need memory to facilitate memory reclaim
+	 */
+	dsocket->sk->sk_allocation = GFP_ATOMIC;
+	csocket->sk->sk_allocation = GFP_ATOMIC;
 
 	dsocket->sk->sk_use_task_frag = false;
 	csocket->sk->sk_use_task_frag = false;
 
+	sk_set_memalloc(dsocket->sk);
+	sk_set_memalloc(csocket->sk);
+
 	dsocket->sk->sk_priority = TC_PRIO_INTERACTIVE_BULK;
 	csocket->sk->sk_priority = TC_PRIO_INTERACTIVE;