lib: Memory spike reduction for sh cmds at scale

The output buffer vty->obuf is a linked list where
each element is of 4KB.
Currently, when a huge sh command  like “show ip route json”
is executed on a large scale, all the vty_out’s are
processed and the entire data is accumulated.
After the entire vty execution, vtysh_flush proceeses
and puts this data in the socket (131KB at a time).

Problem here is the memory spike for such heavy duty
show commands.

The fix here is to chunkify the output on VTY shell by
flushing it intermediately for every 128 KB of output
accumulated and free the memory allocated for the buffer data.

This way, we achieve ~25-30% reduction in the memory spike.

Signed-off-by: Srujana <[email protected]>
Signed-off-by: Rajasekar Raja <[email protected]>
Signed-off-by: Srujana <[email protected]>

lib/vty.c

@@ -345,8 +345,16 @@ int vty_out(struct vty *vty, const char *format, ...)
 	case VTY_SHELL_SERV:
 	case VTY_FILE:
 	default:
+		vty->vty_buf_size_written += strlen(filtered);
 		/* print without crlf replacement */
 		buffer_put(vty->obuf, (uint8_t *)filtered, strlen(filtered));
+		/* For every 32 *4 KB invoke vtysh_flush where we
+		 * put the data of collective vty->obuf Linked List items on the
+		 * socket and free the vty->obuf data. This way, we are flushing
+		 * data every 128KB for the show command.
+		 */
+		if (vty->vty_buf_size_written >= 32 * 4096)
+			vtysh_flush(vty);
 		break;
 	}
 
@@ -2141,6 +2149,21 @@ static void vtysh_accept(struct event *thread)
 		close(sock);
 		return;
 	}
+	/* Setting the SND buffer size to 16MB to increase the buffer size
+	 * the socket can hold before sending it to VTY shell
+	 */
+	uint32_t sndbufsize = 4096*4096;
+	int ret;
+
+	ret = setsockopt(sock, SOL_SOCKET, SO_SNDBUF, (char *)&sndbufsize,
+			 sizeof(sndbufsize));
+	if (ret < 0) {
+		flog_err(EC_LIB_SOCKET,
+			 "Cannot set socket %d send buffer size, %s", sock,
+			 safe_strerror(errno));
+		close(sock);
+		return;
+	}
 	set_cloexec(sock);
 
 #ifdef VTYSH_DEBUG
@@ -2227,6 +2250,7 @@ static int vtysh_flush(struct vty *vty)
 		vty_close(vty);
 		return -1;
 	case BUFFER_EMPTY:
+		vty->vty_buf_size_written =0;
 		break;
 	}
 	return 0;

lib/vty.h

@@ -236,6 +236,7 @@ struct vty {
 	uintptr_t mgmt_req_pending_data;
 	bool mgmt_locked_candidate_ds;
 	bool mgmt_locked_running_ds;
+	uint64_t vty_buf_size_written;
 };
 
 static inline void vty_push_context(struct vty *vty, int node, uint64_t id)

vtysh/vtysh.c

@@ -4721,6 +4721,23 @@ static int vtysh_connect(struct vtysh_client *vclient)
 		close(sock);
 		return -1;
 	}
+	/* Setting the RCV buffer size to 16MB to increase the buffer size
+	 * the socket can hold after receving from other process
+	 */
+	uint32_t rcvbufsize = 4096 * 4096;
+
+	ret = setsockopt(sock, SOL_SOCKET, SO_RCVBUF, (char *)&rcvbufsize,
+			 sizeof(rcvbufsize));
+	if (ret < 0) {
+#ifdef DEBUG
+		fprintf(stderr,
+			"Cannot set socket %d rcv buffer size, %s\n",
+			sock, safe_strerror(errno));
+#endif /* DEBUG */
+		close(sock);
+		return -1;
+	}
+
 	vclient->fd = sock;
 
 	return 0;