public void closeHandler() {
        // On JVM, a memory mapping is typically unmapped by garbage collector.
        // However, in some cases it can pause application threads(STW) for a long moment reading metadata from a physical disk.
        // To prevent this, we forcefully cleanup memory mapping within proper execution which never affects API responsiveness.
        // See https://issues.apache.org/jira/browse/KAFKA-4614 for the details.
        lock.lock();
        try {
            safeForceUnmap();
        } finally {
            lock.unlock();
        }
    }
The number of bytes actually used by this index
storage/src/main/java/org/apache/kafka/storage/internals/log/AbstractIndex.java