Large DirectByteBuffer overhead in Util$BufferCache

Issue

• We see "OutOfMemoryError: Direct buffer memory" errors. The heap dump shows many DirectByteBuffer stored as thread locals by sun.nio.ch.Util$BufferCache:

'- threadLocals java.lang.ThreadLocal$ThreadLocalMap @ 0x52df9aa38       |            1 |           24 |                64 |        41,024
   '- table java.lang.ThreadLocal$ThreadLocalMap$Entry[256] @ 0x51ce090f0|            1 |        1,040 |                64 |        41,000
      '- [184] java.lang.ThreadLocal$ThreadLocalMap$Entry @ 0x52dfc7ef8  |            1 |           32 |                64 |         4,168
         '- value sun.nio.ch.Util$BufferCache @ 0x52dfc7f18              |            1 |           24 |                64 |         4,136
            '- buffers java.nio.ByteBuffer[1024] @ 0x52dfcc510           |            1 |        4,112 |                64 |         4,112
               '- [489] java.nio.DirectByteBuffer @ 0x565d5bb48          |            1 |           64 |                64 |            64