How to identify which app is reading from my disk

Except for disabling one app at a time or all at once and then enable them all slowly again (The Elimination method) - How do I identify what app is reading my disk ? it happens periodically and therefore very hard to debug. What happens is that the phone slows down to an almost unusable state and when opening "System Monitor" (3rd party app) i see that the Disk is reading at 90MB/s. But i cant see WHAT APP is reading ! I've looked everywhere for monitor apps but haven't been able to find anything useful. None of the monitor apps i've found shows the CPU / IO usage of other apps, seems like Android 7.0 is limited in this aspect. My phone (Sony Z5 Compact, Android 7.0) is NOT rooted !