diff --git a/transport/src/main/java/io/netty/channel/DefaultChannelHandlerInvoker.java b/transport/src/main/java/io/netty/channel/DefaultChannelHandlerInvoker.java
index 3d536b1d3e..624b405b4b 100644
--- a/transport/src/main/java/io/netty/channel/DefaultChannelHandlerInvoker.java
+++ b/transport/src/main/java/io/netty/channel/DefaultChannelHandlerInvoker.java
@@ -16,23 +16,14 @@
 
 package io.netty.channel;
 
-import io.netty.buffer.ByteBuf;
-import io.netty.buffer.ByteBufHolder;
 import io.netty.util.Recycler;
 import io.netty.util.ReferenceCountUtil;
 import io.netty.util.concurrent.EventExecutor;
-import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.OneTimeTask;
 import io.netty.util.internal.RecyclableMpscLinkedQueueNode;
+import io.netty.util.internal.SystemPropertyUtil;
 
-import java.lang.reflect.Field;
-import java.lang.reflect.Modifier;
 import java.net.SocketAddress;
-import java.nio.ByteBuffer;
-import java.util.HashSet;
-import java.util.Map;
-import java.util.Set;
-import java.util.WeakHashMap;
 
 import static io.netty.channel.ChannelHandlerInvokerUtil.*;
 import static io.netty.channel.DefaultChannelPipeline.*;
@@ -403,91 +394,13 @@ public class DefaultChannelHandlerInvoker implements ChannelHandlerInvoker {
     static final class WriteTask extends RecyclableMpscLinkedQueueNode<SingleThreadEventLoop.NonWakeupRunnable>
             implements SingleThreadEventLoop.NonWakeupRunnable {
 
-        private static final FastThreadLocal<Map<Class<?>, Integer>> CLASS_SIZES =
-                new FastThreadLocal<Map<Class<?>, Integer>>() {
-                    @Override
-                    protected Map<Class<?>, Integer> initialValue() throws Exception {
-                        Map<Class<?>, Integer> map = new WeakHashMap<Class<?>, Integer>();
-                        map.put(void.class, 0);
-                        map.put(byte.class, 1);
-                        map.put(char.class, 2);
-                        map.put(short.class, 2);
-                        map.put(boolean.class, 4); // Probably an integer.
-                        map.put(int.class, 4);
-                        map.put(float.class, 4);
-                        map.put(long.class, 8);
-                        map.put(double.class, 8);
-                        return map;
-                    }
-                };
+        private static final boolean ESTIMATE_TASK_SIZE_ON_SUBMIT =
+                SystemPropertyUtil.getBoolean("io.netty.transport.estimateSizeOnSubmit", true);
 
-        private static int estimateSize(Object o, Map<Class<?>, Integer> classSizes) {
-            int answer = 8 + estimateSize(o.getClass(), classSizes, null);
+        // Assuming a 64-bit JVM, 16 bytes object header, 3 reference fields and one int field, plus alignment
+        private static final int WRITE_TASK_OVERHEAD =
+                SystemPropertyUtil.getInt("io.netty.transport.writeTaskSizeOverhead", 48);
 
-            if (o instanceof ByteBuf) {
-                answer += ((ByteBuf) o).readableBytes();
-            } else if (o instanceof ByteBufHolder) {
-                answer += ((ByteBufHolder) o).content().readableBytes();
-            } else if (o instanceof FileRegion) {
-                // nothing to add.
-            } else if (o instanceof byte[]) {
-                answer += ((byte[]) o).length;
-            } else if (o instanceof ByteBuffer) {
-                answer += ((ByteBuffer) o).remaining();
-            } else if (o instanceof CharSequence) {
-                answer += ((CharSequence) o).length() << 1;
-            } else if (o instanceof Iterable<?>) {
-                for (Object m : (Iterable<?>) o) {
-                    answer += estimateSize(m, classSizes);
-                }
-            }
-
-            return align(answer);
-        }
-
-        private static int estimateSize(Class<?> clazz, Map<Class<?>, Integer> classSizes,
-                                        Set<Class<?>> visitedClasses) {
-            Integer objectSize = classSizes.get(clazz);
-            if (objectSize != null) {
-                return objectSize;
-            }
-
-            if (visitedClasses != null) {
-                if (visitedClasses.contains(clazz)) {
-                    return 0;
-                }
-            } else {
-                visitedClasses = new HashSet<Class<?>>();
-            }
-
-            visitedClasses.add(clazz);
-
-            int answer = 8; // Basic overhead.
-            for (Class<?> c = clazz; c != null; c = c.getSuperclass()) {
-                Field[] fields = c.getDeclaredFields();
-                for (Field f : fields) {
-                    if ((f.getModifiers() & Modifier.STATIC) != 0) {
-                        // Ignore static fields.
-                        continue;
-                    }
-
-                    answer += estimateSize(f.getType(), classSizes, visitedClasses);
-                }
-            }
-
-            visitedClasses.remove(clazz);
-
-            // Some alignment.
-            answer = align(answer);
-
-            // Put the final answer.
-            classSizes.put(clazz, answer);
-            return answer;
-        }
-
-        private static int align(int size) {
-            return size + 8 - (size & 7);
-        }
         private ChannelHandlerContext ctx;
         private Object msg;
         private ChannelPromise promise;
@@ -506,13 +419,21 @@ public class DefaultChannelHandlerInvoker implements ChannelHandlerInvoker {
             task.ctx = ctx;
             task.msg = msg;
             task.promise = promise;
-            task.size = ((AbstractChannel) ctx.channel()).estimatorHandle().size(msg)
-                    + estimateSize(task, CLASS_SIZES.get());
-            ChannelOutboundBuffer buffer = ctx.channel().unsafe().outboundBuffer();
-            // Check for null as it may be set to null if the channel is closed already
-            if (buffer != null) {
-                buffer.incrementPendingOutboundBytes(task.size);
+
+            if (ESTIMATE_TASK_SIZE_ON_SUBMIT) {
+                ChannelOutboundBuffer buffer = ctx.channel().unsafe().outboundBuffer();
+
+                // Check for null as it may be set to null if the channel is closed already
+                if (buffer != null) {
+                    task.size = ((AbstractChannel) ctx.channel()).estimatorHandle().size(msg) + WRITE_TASK_OVERHEAD;
+                    buffer.incrementPendingOutboundBytes(task.size);
+                } else {
+                    task.size = 0;
+                }
+            } else {
+                task.size = 0;
             }
+
             return task;
         }
 
@@ -525,7 +446,7 @@ public class DefaultChannelHandlerInvoker implements ChannelHandlerInvoker {
             try {
                 ChannelOutboundBuffer buffer = ctx.channel().unsafe().outboundBuffer();
                 // Check for null as it may be set to null if the channel is closed already
-                if (buffer != null) {
+                if (ESTIMATE_TASK_SIZE_ON_SUBMIT && buffer != null) {
                     buffer.decrementPendingOutboundBytes(size);
                 }
                 invokeWriteNow(ctx, msg, promise);