l2arc_log_blk_overhead
l2arc_log_blk_overhead(uint64_t write_sz, l2arc_dev_t *dev);
if ((size + l2arc_log_blk_overhead(size, dev)) >= dev_size) {
l2arc_log_blk_overhead(size, dev),
distance += l2arc_log_blk_overhead(distance, dev);