@Override
    public boolean cleanup(final long currentRef) {
        if (isAvailable()) {
            return false;
        }
        if (isCleanupOver() || !isMapped()) {
            return true;
        }
        unmmap();
        return true;
    }
Flush data to disk
@return The current flushed position
jraft-extension/java-log-storage-impl/src/main/java/com/alipay/sofa/jraft/storage/file/AbstractFile.java