I/O and the court of law

• The first problem is determining - who is the owner of a given I/O?
• Consider these scenarios, and determine who is the owner:
  • Task A wrote to a file - into page-cache. Task B then wrote over the same file-offsets. Data was flushed to disk once
  • Task A read from a file. Task B read from the same file (via page-cache).
  • Task A wrote into a file - into page-cache. Task B read from the file - from the page-cache.
• So who do we "blame" for the I/O operation - who is the scapegoat?
  • The one that happened to "be first to read" for whom disk access was done?
  • Anyone, regardless of whether disk I/O was needed or not?
  • Split the "blame" between all involved?

Originally written by guy keren