Alice and Bob in I/O Land

Table of contents

• Alice, Bob And Their Race To Disk-Haven
• Alice's Adventures In Wonderland - A Partial Recap
  • Alice's Adventures In Wonderland - A Partial Recap - Cont.
• Meet Alice - the 16KB "write" that could
  • Alice goes down the Rabbit hole
  • Alice wants to pass through the small door
  • Little Alice joins the (page-cached) Caucus race
  • Little Alice going down the (disk) elevator
  • Little Alice grows again - the I/O scheduler dance
    • Example of "iostat" output
  • Big Alice plays the disk Crockett - the basic elevator algorithm
  • Original Alice Stands to Trial - ERR_SUCCESS or ERR_IO?
    • Mad Hatter testifies - the small bio-s joining in
  • Original Alice wakes up from her write-full dream
• Ecila - the "read" that came back from the cold
  • Through The Looking Glass - A Partial Recap
    • Through The Looking Glass - A Partial Recap - Cont.
  • Ecila passes through the looking glass
  • Ecila meets the red queen and (page-cachely) runs nowhere
    • What's in my cache?
  • Ecila meets the White Knight and goes to gather herself
  • Ecila and Humpty Dumpty have a great elevated fall
  • Ecila meets Twiddledee and Twiddledum - and sends them ahead
    • Tuning device-level read-ahead
  • Ecila comes back through the mirror
• File-Systems and meta-data I/O
  • Directory hierarchy traversal and the dentry cache
  • File heads and the inode cache
  • File Blocks And File Extents
  • File-System Journaling
• Bob - the raw-"write"-er
  • Bob goes into I/O land
  • To cache or not to cache - that is the D(irect) question
  • What if Bob was sync(ing) harder?
• boB - the reader from the "raw"
  • boB goes catching some ride
  • boB the cached Vs. boB the direct
• Alice and Bob go picking an elevator
  • The "noop" elevator - quick and noisy
  • The "CFQ" elevator - "no room! no room! (at the tea party)"
    • I/O Priority Using "ionice"
  • The "deadline" elevator - "I'm late! I'm late! I'm late!"
  • The "anticipatory" elevator - "If you build it - they will come"
• I/O and the court of law
  • Cartman (from South-park) looking for his father...
  • Why is it so hard to perform per-process I/O accounting
  • /proc/<pid>/io and iotop
  • The I/O law of fatherhood
• References

Originally written by guy keren