NFSv4.1: Ping server when our session table limits are too high

If the server requests a lower target_highest_slotid, then ensure
that we ping it with at least one RPC call containing an
appropriate SEQUENCE op. This ensures that the server won't need to
send a recall callback in order to shrink the slot table.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4_fs.h

@@ -321,6 +321,7 @@ int nfs41_discover_server_trunking(struct nfs_client *clp,
 			struct nfs_client **, struct rpc_cred *);
 extern void nfs4_schedule_session_recovery(struct nfs4_session *, int);
 extern void nfs41_server_notify_target_slotid_update(struct nfs_client *clp);
+extern void nfs41_server_notify_highest_slotid_update(struct nfs_client *clp);
 
 #else
 static inline void nfs4_schedule_session_recovery(struct nfs4_session *session, int err)

fs/nfs/nfs4proc.c

@@ -389,6 +389,7 @@ static void nfs41_sequence_free_slot(struct nfs4_sequence_res *res)
 {
 	struct nfs4_session *session;
 	struct nfs4_slot_table *tbl;
+	bool send_new_highest_used_slotid = false;
 
 	if (!res->sr_slot) {
 		/* just wake up the next guy waiting since
@@ -400,12 +401,25 @@ static void nfs41_sequence_free_slot(struct nfs4_sequence_res *res)
 	session = tbl->session;
 
 	spin_lock(&tbl->slot_tbl_lock);
+	/* Be nice to the server: try to ensure that the last transmitted
+	 * value for highest_user_slotid <= target_highest_slotid
+	 */
+	if (tbl->highest_used_slotid > tbl->target_highest_slotid)
+		send_new_highest_used_slotid = true;
+
 	nfs4_free_slot(tbl, res->sr_slot);
-	if (!nfs4_session_draining(session))
-		rpc_wake_up_first(&tbl->slot_tbl_waitq,
-				nfs4_set_task_privileged, NULL);
+
+	if (tbl->highest_used_slotid != NFS4_NO_SLOT)
+		send_new_highest_used_slotid = false;
+	if (!nfs4_session_draining(session)) {
+		if (rpc_wake_up_first(&tbl->slot_tbl_waitq,
+				nfs4_set_task_privileged, NULL) != NULL)
+			send_new_highest_used_slotid = false;
+	}
 	spin_unlock(&tbl->slot_tbl_lock);
 	res->sr_slot = NULL;
+	if (send_new_highest_used_slotid)
+		nfs41_server_notify_highest_slotid_update(session->clp);
 }
 
 static int nfs41_sequence_done(struct rpc_task *task, struct nfs4_sequence_res *res)

fs/nfs/nfs4state.c

@@ -1961,6 +1961,11 @@ void nfs41_server_notify_target_slotid_update(struct nfs_client *clp)
 	nfs41_ping_server(clp);
 }
 
+void nfs41_server_notify_highest_slotid_update(struct nfs_client *clp)
+{
+	nfs41_ping_server(clp);
+}
+
 static void nfs4_reset_all_state(struct nfs_client *clp)
 {
 	if (test_and_set_bit(NFS4CLNT_LEASE_EXPIRED, &clp->cl_state) == 0) {