private void initCompactionMemoryManager(long compactionMemorySize) {
    long fixedMemoryCost =
        AbstractCompactionEstimator.allocateMemoryCostForFileInfoCache(compactionMemorySize);
    compactionMemoryManager =
        storageEngineMemoryManager.getOrCreateMemoryManager(
            "Compaction", compactionMemorySize - fixedMemoryCost);
  }
The memory manager of direct Buffer
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/conf/DataNodeMemoryConfig.java