[GitHub] spark pull request #19077: [SPARK-21860][core]Improve memory reuse for heap ...

[jerryshao <gi...@git.apache.org>]

Github user jerryshao commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19077#discussion_r136069800
  
    --- Diff: common/unsafe/src/main/java/org/apache/spark/unsafe/memory/HeapMemoryAllocator.java ---
    @@ -47,23 +47,29 @@ private boolean shouldPool(long size) {
     
       @Override
       public MemoryBlock allocate(long size) throws OutOfMemoryError {
    -    if (shouldPool(size)) {
    +    int arraySize = (int)((size + 7) / 8);
    +    long alignedSize = arraySize * 8;
    +    if (shouldPool(alignedSize)) {
           synchronized (this) {
    -        final LinkedList<WeakReference<MemoryBlock>> pool = bufferPoolsBySize.get(size);
    +        final LinkedList<WeakReference<MemoryBlock>> pool = bufferPoolsBySize.get(alignedSize);
             if (pool != null) {
               while (!pool.isEmpty()) {
                 final WeakReference<MemoryBlock> blockReference = pool.pop();
                 final MemoryBlock memory = blockReference.get();
                 if (memory != null) {
    -              assert (memory.size() == size);
    +              assert ((int)((memory.size() + 7) / 8) == arraySize);
    +              memory.resetSize(size);
    --- End diff --
    
    Hmm, from my understanding the size of `MemoryBlock` is always the actual size, not the aligned size, so looks like we dont need to reset the size here.


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