diff --git a/buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java b/buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java
index eceef5072e..2040fdaf3c 100644
--- a/buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java
@@ -230,6 +230,7 @@ public abstract class AbstractByteBuf extends ByteBuf {
         if (minWritableBytes <= writableBytes()) {
             return;
         }
+        final int writerIndex = writerIndex();
         if (checkBounds) {
             if (minWritableBytes > maxCapacity - writerIndex) {
                 throw new IndexOutOfBoundsException(String.format(
@@ -239,7 +240,14 @@ public abstract class AbstractByteBuf extends ByteBuf {
         }
 
         // Normalize the current capacity to the power of 2.
-        int newCapacity = alloc().calculateNewCapacity(writerIndex + minWritableBytes, maxCapacity);
+        int minNewCapacity = writerIndex + minWritableBytes;
+        int newCapacity = alloc().calculateNewCapacity(minNewCapacity, maxCapacity);
+
+        int fastCapacity = writerIndex + maxFastWritableBytes();
+        // Grow by a smaller amount if it will avoid reallocation
+        if (newCapacity > fastCapacity && minNewCapacity <= fastCapacity) {
+            newCapacity = fastCapacity;
+        }
 
         // Adjust to the new capacity.
         capacity(newCapacity);
@@ -266,7 +274,14 @@ public abstract class AbstractByteBuf extends ByteBuf {
         }
 
         // Normalize the current capacity to the power of 2.
-        int newCapacity = alloc().calculateNewCapacity(writerIndex + minWritableBytes, maxCapacity);
+        int minNewCapacity = writerIndex + minWritableBytes;
+        int newCapacity = alloc().calculateNewCapacity(minNewCapacity, maxCapacity);
+
+        int fastCapacity = writerIndex + maxFastWritableBytes();
+        // Grow by a smaller amount if it will avoid reallocation
+        if (newCapacity > fastCapacity && minNewCapacity <= fastCapacity) {
+            newCapacity = fastCapacity;
+        }
 
         // Adjust to the new capacity.
         capacity(newCapacity);
diff --git a/buffer/src/main/java/io/netty/buffer/ByteBuf.java b/buffer/src/main/java/io/netty/buffer/ByteBuf.java
index 993761f999..25afdf1f8e 100644
--- a/buffer/src/main/java/io/netty/buffer/ByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/ByteBuf.java
@@ -236,7 +236,6 @@ import java.nio.charset.UnsupportedCharsetException;
  * Please refer to {@link ByteBufInputStream} and
  * {@link ByteBufOutputStream}.
  */
-@SuppressWarnings("ClassMayBeInterface")
 public abstract class ByteBuf implements ReferenceCounted, Comparable<ByteBuf> {
 
     /**
@@ -413,6 +412,15 @@ public abstract class ByteBuf implements ReferenceCounted, Comparable<ByteBuf> {
      */
     public abstract int maxWritableBytes();
 
+    /**
+     * Returns the maximum number of bytes which can be written for certain without involving
+     * an internal reallocation or data-copy. The returned value will be &ge; {@link #writableBytes()}
+     * and &le; {@link #maxWritableBytes()}.
+     */
+    public int maxFastWritableBytes() {
+        return writableBytes();
+    }
+
     /**
      * Returns {@code true}
      * if and only if {@code (this.writerIndex - this.readerIndex)} is greater
diff --git a/buffer/src/main/java/io/netty/buffer/PooledByteBuf.java b/buffer/src/main/java/io/netty/buffer/PooledByteBuf.java
index d957a3f547..c842cb68eb 100644
--- a/buffer/src/main/java/io/netty/buffer/PooledByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/PooledByteBuf.java
@@ -81,6 +81,11 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
         return length;
     }
 
+    @Override
+    public int maxFastWritableBytes() {
+        return Math.min(maxLength, maxCapacity()) - writerIndex;
+    }
+
     @Override
     public final ByteBuf capacity(int newCapacity) {
         checkNewCapacity(newCapacity);
diff --git a/buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java b/buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java
index 1da1f12055..f16ae9087e 100644
--- a/buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java
@@ -149,6 +149,11 @@ public class SwappedByteBuf extends ByteBuf {
         return buf.maxWritableBytes();
     }
 
+    @Override
+    public int maxFastWritableBytes() {
+        return buf.maxFastWritableBytes();
+    }
+
     @Override
     public boolean isReadable() {
         return buf.isReadable();
diff --git a/buffer/src/main/java/io/netty/buffer/WrappedByteBuf.java b/buffer/src/main/java/io/netty/buffer/WrappedByteBuf.java
index 29d5919b66..c7c1eec63e 100644
--- a/buffer/src/main/java/io/netty/buffer/WrappedByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/WrappedByteBuf.java
@@ -151,6 +151,11 @@ class WrappedByteBuf extends ByteBuf {
         return buf.maxWritableBytes();
     }
 
+    @Override
+    public int maxFastWritableBytes() {
+        return buf.maxFastWritableBytes();
+    }
+
     @Override
     public final boolean isReadable() {
         return buf.isReadable();
diff --git a/buffer/src/main/java/io/netty/buffer/WrappedCompositeByteBuf.java b/buffer/src/main/java/io/netty/buffer/WrappedCompositeByteBuf.java
index 23a523a2c5..4f0bdd239b 100644
--- a/buffer/src/main/java/io/netty/buffer/WrappedCompositeByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/WrappedCompositeByteBuf.java
@@ -98,6 +98,11 @@ class WrappedCompositeByteBuf extends CompositeByteBuf {
         return wrapped.maxWritableBytes();
     }
 
+    @Override
+    public int maxFastWritableBytes() {
+        return wrapped.maxFastWritableBytes();
+    }
+
     @Override
     public int ensureWritable(int minWritableBytes, boolean force) {
         return wrapped.ensureWritable(minWritableBytes, force);
diff --git a/buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java b/buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java
index b88f3180c5..52e5e4efa5 100644
--- a/buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java
+++ b/buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java
@@ -4846,4 +4846,16 @@ public abstract class AbstractByteBufTest {
             buffer.release();
         }
     }
+
+    @Test
+    public void testMaxFastWritableBytes() {
+        ByteBuf buffer = newBuffer(150, 500).writerIndex(100);
+        assertEquals(50, buffer.writableBytes());
+        assertEquals(150, buffer.capacity());
+        assertEquals(500, buffer.maxCapacity());
+        assertEquals(400, buffer.maxWritableBytes());
+        // Default implementation has fast writable == writable
+        assertEquals(50, buffer.maxFastWritableBytes());
+        buffer.release();
+    }
 }
diff --git a/buffer/src/test/java/io/netty/buffer/AbstractPooledByteBufTest.java b/buffer/src/test/java/io/netty/buffer/AbstractPooledByteBufTest.java
index 902548d2f3..c3b2a104d0 100644
--- a/buffer/src/test/java/io/netty/buffer/AbstractPooledByteBufTest.java
+++ b/buffer/src/test/java/io/netty/buffer/AbstractPooledByteBufTest.java
@@ -21,6 +21,8 @@ import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 public abstract class AbstractPooledByteBufTest extends AbstractByteBufTest {
@@ -55,4 +57,61 @@ public abstract class AbstractPooledByteBufTest extends AbstractByteBufTest {
             buf.release();
         }
     }
+
+    @Override
+    @Test
+    public void testMaxFastWritableBytes() {
+        ByteBuf buffer = newBuffer(150, 500).writerIndex(100);
+        assertEquals(50, buffer.writableBytes());
+        assertEquals(150, buffer.capacity());
+        assertEquals(500, buffer.maxCapacity());
+        assertEquals(400, buffer.maxWritableBytes());
+
+        int chunkSize = pooledByteBuf(buffer).maxLength;
+        assertTrue(chunkSize >= 150);
+        int remainingInAlloc = Math.min(chunkSize - 100, 400);
+        assertEquals(remainingInAlloc, buffer.maxFastWritableBytes());
+
+        // write up to max, chunk alloc should not change (same handle)
+        long handleBefore = pooledByteBuf(buffer).handle;
+        buffer.writeBytes(new byte[remainingInAlloc]);
+        assertEquals(handleBefore, pooledByteBuf(buffer).handle);
+
+        assertEquals(0, buffer.maxFastWritableBytes());
+        // writing one more should trigger a reallocation (new handle)
+        buffer.writeByte(7);
+        assertNotEquals(handleBefore, pooledByteBuf(buffer).handle);
+
+        // should not exceed maxCapacity even if chunk alloc does
+        buffer.capacity(500);
+        assertEquals(500 - buffer.writerIndex(), buffer.maxFastWritableBytes());
+        buffer.release();
+    }
+
+    private static PooledByteBuf<?> pooledByteBuf(ByteBuf buffer) {
+        // might need to unwrap if swapped (LE) and/or leak-aware-wrapped
+        while (!(buffer instanceof PooledByteBuf)) {
+            buffer = buffer.unwrap();
+        }
+        return (PooledByteBuf<?>) buffer;
+    }
+
+    @Test
+    public void testEnsureWritableDoesntGrowTooMuch() {
+        ByteBuf buffer = newBuffer(150, 500).writerIndex(100);
+
+        assertEquals(50, buffer.writableBytes());
+        int fastWritable = buffer.maxFastWritableBytes();
+        assertTrue(fastWritable > 50);
+
+        long handleBefore = pooledByteBuf(buffer).handle;
+
+        // capacity expansion should not cause reallocation
+        // (should grow precisely the specified amount)
+        buffer.ensureWritable(fastWritable);
+        assertEquals(handleBefore, pooledByteBuf(buffer).handle);
+        assertEquals(100 + fastWritable, buffer.capacity());
+        assertEquals(buffer.writableBytes(), buffer.maxFastWritableBytes());
+        buffer.release();
+    }
 }