Revert "Provide a way to cache the internal nioBuffer of the PooledByteBuffer to reduce GC. (#8593)"

This reverts commit 8cd005ba43 as it seems to produce some failures in some cases. This needs more research.

buffer/src/main/java/io/netty/buffer/PoolChunk.java

@@ -16,10 +16,6 @@
 
 package io.netty.buffer;
 
-import java.nio.ByteBuffer;
-import java.util.ArrayDeque;
-import java.util.Deque;
-
 /**
  * Description of algorithm for PageRun/PoolSubpage allocation from PoolChunk
  *
@@ -111,6 +107,7 @@ final class PoolChunk<T> implements PoolChunkMetric {
     final T memory;
     final boolean unpooled;
     final int offset;
+
     private final byte[] memoryMap;
     private final byte[] depthMap;
     private final PoolSubpage<T>[] subpages;
@@ -125,13 +122,6 @@ final class PoolChunk<T> implements PoolChunkMetric {
     /** Used to mark memory as unusable */
     private final byte unusable;
 
-    // Use as cache for ByteBuffer created from the memory. These are just duplicates and so are only a container
-    // around the memory itself. These are often needed for operations within the Pooled*DirectByteBuf and so
-    // may produce extra GC, which can be greatly reduced by caching the duplicates.
-    //
-    // This may be null if the PoolChunk is unpooled as pooling the ByteBuffer instances does not make any sense here.
-    private final Deque<ByteBuffer> cachedNioBuffers;
-
     private int freeBytes;
 
     PoolChunkList<T> parent;
@@ -173,7 +163,6 @@ final class PoolChunk<T> implements PoolChunkMetric {
         }
 
         subpages = newSubpageArray(maxSubpageAllocs);
-        cachedNioBuffers = new ArrayDeque<ByteBuffer>();
     }
 
     /** Creates a special chunk that is not pooled. */
@@ -193,21 +182,6 @@ final class PoolChunk<T> implements PoolChunkMetric {
         chunkSize = size;
         log2ChunkSize = log2(chunkSize);
         maxSubpageAllocs = 0;
-        cachedNioBuffers = null;
-    }
-
-    ByteBuffer pollCachedNioBuffer() {
-        // We use LIFO to increase the chance that its still "hot" and so in the CPU / L* cache.
-        return cachedNioBuffers != null ? cachedNioBuffers.pollLast() : null;
-    }
-
-    void offerCachedNioBuffer(ByteBuffer nioBuffer) {
-        // Only cache if we did not reach the limit yet and if its not unpooled.
-        // If we do just drop it on the floor and let the GC collect it.
-        if (cachedNioBuffers != null &&
-                cachedNioBuffers.size() <= PooledByteBufAllocator.DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK) {
-            cachedNioBuffers.offer(nioBuffer);
-        }
     }
 
     @SuppressWarnings("unchecked")

buffer/src/main/java/io/netty/buffer/PooledByteBuf.java

@@ -56,13 +56,13 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
 
         this.chunk = chunk;
         memory = chunk.memory;
-        tmpNioBuf = chunk.pollCachedNioBuffer();
         allocator = chunk.arena.parent;
         this.cache = cache;
         this.handle = handle;
         this.offset = offset;
         this.length = length;
         this.maxLength = maxLength;
+        tmpNioBuf = null;
     }
 
     /**
@@ -166,11 +166,7 @@ abstract class PooledByteBuf<T> extends AbstractReferenceCountedByteBuf {
             final long handle = this.handle;
             this.handle = -1;
             memory = null;
-            if (tmpNioBuf != null) {
+            tmpNioBuf = null;
-                // Try to put back into the cache for later usage.
-                chunk.offerCachedNioBuffer(tmpNioBuf);
-                tmpNioBuf = null;
-            }
             chunk.arena.free(chunk, handle, maxLength, cache);
             chunk = null;
             recycle();

buffer/src/main/java/io/netty/buffer/PooledByteBufAllocator.java

@@ -45,7 +45,6 @@ public class PooledByteBufAllocator extends AbstractByteBufAllocator implements
     private static final int DEFAULT_CACHE_TRIM_INTERVAL;
     private static final boolean DEFAULT_USE_CACHE_FOR_ALL_THREADS;
     private static final int DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT;
-    static final int DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK;
 
     private static final int MIN_PAGE_SIZE = 4096;
     private static final int MAX_CHUNK_SIZE = (int) (((long) Integer.MAX_VALUE + 1) / 2);
@@ -117,9 +116,6 @@ public class PooledByteBufAllocator extends AbstractByteBufAllocator implements
         DEFAULT_DIRECT_MEMORY_CACHE_ALIGNMENT = SystemPropertyUtil.getInt(
                 "io.netty.allocator.directMemoryCacheAlignment", 0);
 
-        DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK = SystemPropertyUtil.getInt(
-                "io.netty.allocator.maxCachedByteBuffersPerChunk", 1024);
-
         if (logger.isDebugEnabled()) {
             logger.debug("-Dio.netty.allocator.numHeapArenas: {}", DEFAULT_NUM_HEAP_ARENA);
             logger.debug("-Dio.netty.allocator.numDirectArenas: {}", DEFAULT_NUM_DIRECT_ARENA);
@@ -140,8 +136,6 @@ public class PooledByteBufAllocator extends AbstractByteBufAllocator implements
             logger.debug("-Dio.netty.allocator.maxCachedBufferCapacity: {}", DEFAULT_MAX_CACHED_BUFFER_CAPACITY);
             logger.debug("-Dio.netty.allocator.cacheTrimInterval: {}", DEFAULT_CACHE_TRIM_INTERVAL);
             logger.debug("-Dio.netty.allocator.useCacheForAllThreads: {}", DEFAULT_USE_CACHE_FOR_ALL_THREADS);
-            logger.debug("-Dio.netty.allocator.maxCachedByteBuffersPerChunk: {}",
-                    DEFAULT_MAX_CACHED_BYTEBUFFERS_PER_CHUNK);
         }
     }