cluster: don't silently drop messages when the write queue gets big

lib/child_process.js

@@ -117,11 +117,6 @@ function setupChannel(target, channel) {
 
     if (!target._channel) throw new Error("channel closed");
 
-    // For overflow protection don't write if channel queue is too deep.
-    if (channel.writeQueueSize > 1024 * 1024) {
-      return false;
-    }
-
     var buffer = Buffer(JSON.stringify(message) + '\n');
 
     if (sendHandle && setSimultaneousAccepts) {
@@ -137,7 +132,8 @@ function setupChannel(target, channel) {
 
     writeReq.oncomplete = nop;
 
-    return true;
+    /* If the master is > 2 read() calls behind, please stop sending. */
+    return channel.writeQueueSize < (65536 * 2);
   };
 
   channel.readStart();