RDS: add stat for socket recv memory usage

Tracks the receive side memory added to scokets and removed from sockets.
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>

net/rds/rds.h

@@ -631,6 +631,9 @@ struct rds_statistics {
 	uint64_t	s_cong_update_received;
 	uint64_t	s_cong_send_error;
 	uint64_t	s_cong_send_blocked;
+	uint64_t	s_recv_bytes_added_to_socket;
+	uint64_t	s_recv_bytes_removed_from_socket;
+
 };
 
 /* af_rds.c */

net/rds/recv.c

@@ -94,6 +94,10 @@ static void rds_recv_rcvbuf_delta(struct rds_sock *rs, struct sock *sk,
 		return;
 
 	rs->rs_rcv_bytes += delta;
+	if (delta > 0)
+		rds_stats_add(s_recv_bytes_added_to_socket, delta);
+	else
+		rds_stats_add(s_recv_bytes_removed_from_socket, -delta);
 	now_congested = rs->rs_rcv_bytes > rds_sk_rcvbuf(rs);
 
 	rdsdebug("rs %p (%pI4:%u) recv bytes %d buf %d "