diff --git a/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java b/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java
index 2ed83ad6f7..a54e3af64f 100644
--- a/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeDirectByteBuf.java
@@ -37,10 +37,10 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
     private final ByteBufAllocator alloc;
 
     private long memoryAddress;
-    private ByteBuffer buffer;
     private ByteBuffer tmpNioBuf;
     private int capacity;
     private boolean doNotFree;
+    ByteBuffer buffer;
 
     /**
      * Creates a new direct buffer.
@@ -65,7 +65,7 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
         }
 
         this.alloc = alloc;
-        setByteBuffer(allocateDirect(initialCapacity));
+        setByteBuffer(allocateDirect(initialCapacity), false);
     }
 
     /**
@@ -96,7 +96,7 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
 
         this.alloc = alloc;
         doNotFree = true;
-        setByteBuffer(initialBuffer.slice().order(ByteOrder.BIG_ENDIAN));
+        setByteBuffer(initialBuffer.slice().order(ByteOrder.BIG_ENDIAN), false);
         writerIndex(initialCapacity);
     }
 
@@ -114,16 +114,17 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
         PlatformDependent.freeDirectBuffer(buffer);
     }
 
-    private void setByteBuffer(ByteBuffer buffer) {
-        ByteBuffer oldBuffer = this.buffer;
-        if (oldBuffer != null) {
-            if (doNotFree) {
-                doNotFree = false;
-            } else {
-                freeDirect(oldBuffer);
+    final void setByteBuffer(ByteBuffer buffer, boolean tryFree) {
+        if (tryFree) {
+            ByteBuffer oldBuffer = this.buffer;
+            if (oldBuffer != null) {
+                if (doNotFree) {
+                    doNotFree = false;
+                } else {
+                    freeDirect(oldBuffer);
+                }
             }
         }
-
         this.buffer = buffer;
         memoryAddress = PlatformDependent.directBufferAddress(buffer);
         tmpNioBuf = null;
@@ -158,7 +159,7 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
             newBuffer.position(0).limit(oldBuffer.capacity());
             newBuffer.put(oldBuffer);
             newBuffer.clear();
-            setByteBuffer(newBuffer);
+            setByteBuffer(newBuffer, true);
         } else if (newCapacity < oldCapacity) {
             ByteBuffer oldBuffer = buffer;
             ByteBuffer newBuffer = allocateDirect(newCapacity);
@@ -173,7 +174,7 @@ public class UnpooledUnsafeDirectByteBuf extends AbstractReferenceCountedByteBuf
             } else {
                 setIndex(newCapacity, newCapacity);
             }
-            setByteBuffer(newBuffer);
+            setByteBuffer(newBuffer, true);
         }
         return this;
     }
diff --git a/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeNoCleanerDirectByteBuf.java b/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeNoCleanerDirectByteBuf.java
index 5011a1a520..98899a75be 100644
--- a/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeNoCleanerDirectByteBuf.java
+++ b/buffer/src/main/java/io/netty/buffer/UnpooledUnsafeNoCleanerDirectByteBuf.java
@@ -34,4 +34,39 @@ final class UnpooledUnsafeNoCleanerDirectByteBuf extends UnpooledUnsafeDirectByt
     protected void freeDirect(ByteBuffer buffer) {
         PlatformDependent.freeDirectNoCleaner(buffer);
     }
+
+    @Override
+    public ByteBuf capacity(int newCapacity) {
+        ensureAccessible();
+        if (newCapacity < 0 || newCapacity > maxCapacity()) {
+            throw new IllegalArgumentException("newCapacity: " + newCapacity);
+        }
+
+        int readerIndex = readerIndex();
+        int writerIndex = writerIndex();
+        int oldCapacity = capacity();
+
+        if (newCapacity > oldCapacity) {
+            ByteBuffer oldBuffer = buffer;
+            ByteBuffer newBuffer = PlatformDependent.reallocateDirectNoCleaner(oldBuffer, newCapacity);
+            setByteBuffer(newBuffer, false);
+        } else if (newCapacity < oldCapacity) {
+            ByteBuffer oldBuffer = buffer;
+            ByteBuffer newBuffer = allocateDirect(newCapacity);
+            if (readerIndex < newCapacity) {
+                if (writerIndex > newCapacity) {
+                    writerIndex = newCapacity;
+                    writerIndex(writerIndex);
+                }
+                oldBuffer.position(readerIndex).limit(writerIndex);
+                newBuffer.position(readerIndex).limit(writerIndex);
+                newBuffer.put(oldBuffer);
+                newBuffer.clear();
+            } else {
+                setIndex(newCapacity, newCapacity);
+            }
+            setByteBuffer(newBuffer, true);
+        }
+        return this;
+    }
 }
diff --git a/common/src/main/java/io/netty/util/internal/PlatformDependent.java b/common/src/main/java/io/netty/util/internal/PlatformDependent.java
index fb7ffef18e..214aba2f94 100644
--- a/common/src/main/java/io/netty/util/internal/PlatformDependent.java
+++ b/common/src/main/java/io/netty/util/internal/PlatformDependent.java
@@ -543,25 +543,29 @@ public final class PlatformDependent {
     public static ByteBuffer allocateDirectNoCleaner(int capacity) {
         assert USE_DIRECT_BUFFER_NO_CLEANER;
 
-        if (DIRECT_MEMORY_COUNTER != null) {
-            for (;;) {
-                long usedMemory = DIRECT_MEMORY_COUNTER.get();
-                long newUsedMemory = usedMemory + capacity;
-                if (newUsedMemory > DIRECT_MEMORY_LIMIT) {
-                    throw new OutOfDirectMemoryError("failed to allocate " + capacity
-                            + " byte(s) of direct memory (used: " + usedMemory + ", max: " + DIRECT_MEMORY_LIMIT + ')');
-                }
-                if (DIRECT_MEMORY_COUNTER.compareAndSet(usedMemory, newUsedMemory)) {
-                    break;
-                }
-            }
-        }
+        incrementMemoryCounter(capacity);
         try {
             return PlatformDependent0.allocateDirectNoCleaner(capacity);
         } catch (Throwable e) {
-            if (DIRECT_MEMORY_COUNTER != null) {
-                DIRECT_MEMORY_COUNTER.addAndGet(-capacity);
-            }
+            decrementMemoryCounter(capacity);
+            throwException(e);
+            return null;
+        }
+    }
+
+    /**
+     * Reallocate a new {@link ByteBuffer} with the given {@code capacity}. {@link ByteBuffer}s reallocated with
+     * this method <strong>MUST</strong> be deallocated via {@link #freeDirectNoCleaner(ByteBuffer)}.
+     */
+    public static ByteBuffer reallocateDirectNoCleaner(ByteBuffer buffer, int capacity) {
+        assert USE_DIRECT_BUFFER_NO_CLEANER;
+
+        int len = capacity - buffer.capacity();
+        incrementMemoryCounter(len);
+        try {
+            return PlatformDependent0.reallocateDirectNoCleaner(buffer, capacity);
+        } catch (Throwable e) {
+            decrementMemoryCounter(len);
             throwException(e);
             return null;
         }
@@ -576,6 +580,26 @@ public final class PlatformDependent {
 
         int capacity = buffer.capacity();
         PlatformDependent0.freeMemory(PlatformDependent0.directBufferAddress(buffer));
+        decrementMemoryCounter(capacity);
+    }
+
+    private static void incrementMemoryCounter(int capacity) {
+        if (DIRECT_MEMORY_COUNTER != null) {
+            for (;;) {
+                long usedMemory = DIRECT_MEMORY_COUNTER.get();
+                long newUsedMemory = usedMemory + capacity;
+                if (newUsedMemory > DIRECT_MEMORY_LIMIT) {
+                    throw new OutOfDirectMemoryError("failed to allocate " + capacity
+                            + " byte(s) of direct memory (used: " + usedMemory + ", max: " + DIRECT_MEMORY_LIMIT + ')');
+                }
+                if (DIRECT_MEMORY_COUNTER.compareAndSet(usedMemory, newUsedMemory)) {
+                    break;
+                }
+            }
+        }
+    }
+
+    private static void decrementMemoryCounter(int capacity) {
         if (DIRECT_MEMORY_COUNTER != null) {
             long usedMemory = DIRECT_MEMORY_COUNTER.addAndGet(-capacity);
             assert usedMemory >= 0;
diff --git a/common/src/main/java/io/netty/util/internal/PlatformDependent0.java b/common/src/main/java/io/netty/util/internal/PlatformDependent0.java
index aebfff81b6..98801528fd 100644
--- a/common/src/main/java/io/netty/util/internal/PlatformDependent0.java
+++ b/common/src/main/java/io/netty/util/internal/PlatformDependent0.java
@@ -228,9 +228,15 @@ final class PlatformDependent0 {
         return DIRECT_BUFFER_CONSTRUCTOR != null;
     }
 
+    static ByteBuffer reallocateDirectNoCleaner(ByteBuffer buffer, int capacity) {
+        return newDirectBuffer(UNSAFE.reallocateMemory(directBufferAddress(buffer), capacity), capacity);
+    }
+
     static ByteBuffer allocateDirectNoCleaner(int capacity) {
-        assert DIRECT_BUFFER_CONSTRUCTOR != null;
-        long address = UNSAFE.allocateMemory(capacity);
+        return newDirectBuffer(UNSAFE.allocateMemory(capacity), capacity);
+    }
+
+    private static ByteBuffer newDirectBuffer(long address, int capacity) {
         try {
             return (ByteBuffer) DIRECT_BUFFER_CONSTRUCTOR.newInstance(address, capacity);
         } catch (Throwable cause) {