This read-only integer reports 'dirty' memory that might need writing to disk or swap before it can be freed, such as files that haven't been flushed yet in order to keep I/O down (for example, batching log writes). An admin watches this to understand how much memory reclaim would require disk writes rather than being instantly freeable, which affects how quickly the system can respond to sudden memory demand. For example, a large inactive-dirty value on a system about to run a memory-hungry batch job would warn an admin that reclaiming that memory may cause a burst of disk I/O rather than being instantaneous.