rds: deliver zerocopy completion notification with data

This commit is an optimization over commit 01883eda72bd
("rds: support for zcopy completion notification") for PF_RDS sockets.

RDS applications are predominantly request-response transactions, so
it is more efficient to reduce the number of system calls and have
zerocopy completion notification delivered as ancillary data on the
POLLIN channel.

Cookies are passed up as ancillary data (at level SOL_RDS) in a
struct rds_zcopy_cookies when the returned value of recvmsg() is
greater than, or equal to, 0. A max of RDS_MAX_ZCOOKIES may be passed
with each message.

This commit removes support for zerocopy completion notification on
MSG_ERRQUEUE for PF_RDS sockets.

Signed-off-by: Sowmini Varadhan <[e-mail]>
Acked-by: Willem de Bruijn <[e-mail]>
Acked-by: Santosh Shilimkar <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/errqueue.h

···
 #define SO_EE_ORIGIN_ICMP6	3
 #define SO_EE_ORIGIN_TXSTATUS	4
 #define SO_EE_ORIGIN_ZEROCOPY	5
-#define SO_EE_ORIGIN_ZCOOKIE	6
 #define SO_EE_ORIGIN_TIMESTAMPING SO_EE_ORIGIN_TXSTATUS
 
 #define SO_EE_OFFENDER(ee)	((struct sockaddr*)((ee)+1))
 
 #define SO_EE_CODE_ZEROCOPY_COPIED	1
-#define	SO_EE_ORIGIN_MAX_ZCOOKIES	8
 
 /**
  *	struct scm_timestamping - timestamps exposed through cmsg

include/uapi/linux/rds.h

···
 #define RDS_CMSG_MASKED_ATOMIC_CSWP	9
 #define RDS_CMSG_RXPATH_LATENCY		11
 #define	RDS_CMSG_ZCOPY_COOKIE		12
+#define	RDS_CMSG_ZCOPY_COMPLETION	13
 
 #define RDS_INFO_FIRST			10000
 #define RDS_INFO_COUNTERS		10000
···
 #define RDS_RDMA_CANCELED	2
 #define RDS_RDMA_DROPPED	3
 #define RDS_RDMA_OTHER_ERROR	4
+
+#define	RDS_MAX_ZCOOKIES	8
+struct rds_zcopy_cookies {
+	__u32 num;
+	__u32 cookies[RDS_MAX_ZCOOKIES];
+};
 
 /*
  * Common set of flags for all RDMA related structs

net/rds/af_rds.c

···
 	rds_send_drop_to(rs, NULL);
 	rds_rdma_drop_keys(rs);
 	rds_notify_queue_get(rs, NULL);
+	__skb_queue_purge(&rs->rs_zcookie_queue);
 
 	spin_lock_bh(&rds_sock_lock);
 	list_del_init(&rs->rs_item);
···
  *  -	to signal that a previously congested destination may have become
  *	uncongested
  *  -	A notification has been queued to the socket (this can be a congestion
- *	update, or a RDMA completion).
+ *	update, or a RDMA completion, or a MSG_ZEROCOPY completion).
  *
  * EPOLLOUT is asserted if there is room on the send queue. This does not mean
  * however, that the next sendmsg() call will succeed. If the application tries
···
 		spin_unlock(&rs->rs_lock);
 	}
 	if (!list_empty(&rs->rs_recv_queue) ||
-	    !list_empty(&rs->rs_notify_queue))
+	    !list_empty(&rs->rs_notify_queue) ||
+	    !skb_queue_empty(&rs->rs_zcookie_queue))
 		mask |= (EPOLLIN | EPOLLRDNORM);
 	if (rs->rs_snd_bytes < rds_sk_sndbuf(rs))
 		mask |= (EPOLLOUT | EPOLLWRNORM);
···
 	INIT_LIST_HEAD(&rs->rs_recv_queue);
 	INIT_LIST_HEAD(&rs->rs_notify_queue);
 	INIT_LIST_HEAD(&rs->rs_cong_list);
+	skb_queue_head_init(&rs->rs_zcookie_queue);
 	spin_lock_init(&rs->rs_rdma_lock);
 	rs->rs_rdma_keys = RB_ROOT;
 	rs->rs_rx_traces = 0;

net/rds/message.c

···
 
 static inline bool skb_zcookie_add(struct sk_buff *skb, u32 cookie)
 {
-	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
-	int ncookies;
-	u32 *ptr;
+	struct rds_zcopy_cookies *ck = (struct rds_zcopy_cookies *)skb->cb;
+	int ncookies = ck->num;
 
-	if (serr->ee.ee_origin != SO_EE_ORIGIN_ZCOOKIE)
+	if (ncookies == RDS_MAX_ZCOOKIES)
 		return false;
-	ncookies = serr->ee.ee_data;
-	if (ncookies == SO_EE_ORIGIN_MAX_ZCOOKIES)
-		return false;
-	ptr = skb_put(skb, sizeof(u32));
-	*ptr = cookie;
-	serr->ee.ee_data = ++ncookies;
+	ck->cookies[ncookies] = cookie;
+	ck->num =  ++ncookies;
 	return true;
 }
 
 static void rds_rm_zerocopy_callback(struct rds_sock *rs,
 				     struct rds_znotifier *znotif)
 {
-	struct sock *sk = rds_rs_to_sk(rs);
 	struct sk_buff *skb, *tail;
-	struct sock_exterr_skb *serr;
 	unsigned long flags;
 	struct sk_buff_head *q;
 	u32 cookie = znotif->z_cookie;
+	struct rds_zcopy_cookies *ck;
 
-	q = &sk->sk_error_queue;
+	q = &rs->rs_zcookie_queue;
 	spin_lock_irqsave(&q->lock, flags);
 	tail = skb_peek_tail(q);
 
···
 		spin_unlock_irqrestore(&q->lock, flags);
 		mm_unaccount_pinned_pages(&znotif->z_mmp);
 		consume_skb(rds_skb_from_znotifier(znotif));
-		sk->sk_error_report(sk);
+		/* caller invokes rds_wake_sk_sleep() */
 		return;
 	}
 
 	skb = rds_skb_from_znotifier(znotif);
-	serr = SKB_EXT_ERR(skb);
-	memset(&serr->ee, 0, sizeof(serr->ee));
-	serr->ee.ee_errno = 0;
-	serr->ee.ee_origin = SO_EE_ORIGIN_ZCOOKIE;
-	serr->ee.ee_info = 0;
+	ck = (struct rds_zcopy_cookies *)skb->cb;
+	memset(ck, 0, sizeof(*ck));
 	WARN_ON(!skb_zcookie_add(skb, cookie));
 
 	__skb_queue_tail(q, skb);
 
 	spin_unlock_irqrestore(&q->lock, flags);
-	sk->sk_error_report(sk);
+	/* caller invokes rds_wake_sk_sleep() */
 
 	mm_unaccount_pinned_pages(&znotif->z_mmp);
 }
···
 		if (rm->data.op_mmp_znotifier) {
 			zcopy = true;
 			rds_rm_zerocopy_callback(rs, rm->data.op_mmp_znotifier);
+			rds_wake_sk_sleep(rs);
 			rm->data.op_mmp_znotifier = NULL;
 		}
 		sock_put(rds_rs_to_sk(rs));
···
 		int total_copied = 0;
 		struct sk_buff *skb;
 
-		skb = alloc_skb(SO_EE_ORIGIN_MAX_ZCOOKIES * sizeof(u32),
-				GFP_KERNEL);
+		skb = alloc_skb(0, GFP_KERNEL);
 		if (!skb)
 			return -ENOMEM;
+		BUILD_BUG_ON(sizeof(skb->cb) <
+			     max_t(int, sizeof(struct rds_znotifier),
+				   sizeof(struct rds_zcopy_cookies)));
 		rm->data.op_mmp_znotifier = RDS_ZCOPY_SKB(skb);
 		if (mm_account_pinned_pages(&rm->data.op_mmp_znotifier->z_mmp,
 					    length)) {

net/rds/rds.h

···
 	/* Socket receive path trace points*/
 	u8			rs_rx_traces;
 	u8			rs_rx_trace[RDS_MSG_RX_DGRAM_TRACE_MAX];
+
+	struct sk_buff_head	rs_zcookie_queue;
 };
 
 static inline struct rds_sock *rds_sk_to_rs(const struct sock *sk)

net/rds/recv.c

···
 	return ret;
 }
 
+static bool rds_recvmsg_zcookie(struct rds_sock *rs, struct msghdr *msg)
+{
+	struct sk_buff *skb;
+	struct sk_buff_head *q = &rs->rs_zcookie_queue;
+	struct rds_zcopy_cookies *done;
+
+	if (!msg->msg_control)
+		return false;
+
+	if (!sock_flag(rds_rs_to_sk(rs), SOCK_ZEROCOPY) ||
+	    msg->msg_controllen < CMSG_SPACE(sizeof(*done)))
+		return false;
+
+	skb = skb_dequeue(q);
+	if (!skb)
+		return false;
+	done = (struct rds_zcopy_cookies *)skb->cb;
+	if (put_cmsg(msg, SOL_RDS, RDS_CMSG_ZCOPY_COMPLETION, sizeof(*done),
+		     done)) {
+		skb_queue_head(q, skb);
+		return false;
+	}
+	consume_skb(skb);
+	return true;
+}
+
 int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		int msg_flags)
 {
···
 
 		if (!rds_next_incoming(rs, &inc)) {
 			if (nonblock) {
-				ret = -EAGAIN;
+				bool reaped = rds_recvmsg_zcookie(rs, msg);
+
+				ret = reaped ?  0 : -EAGAIN;
 				break;
 			}
 
···
 			ret = -EFAULT;
 			goto out;
 		}
+		rds_recvmsg_zcookie(rs, msg);
 
 		rds_stats_inc(s_recv_delivered);