A very basic ruby script for defragmenting files on btrfs loaded by preload daemon

defrag-preloaded.rb

#!/bin/env ruby
#
# basic concept script for defragmenting files on btrfs loaded by preload daemon
#
# Actually, this idea is working in the spirit of systemd's readahead function which
# can defrag (and relocate?) files on btrfs during boot. Preload takes on where
# readahead stops working, so it should be a great place to continue integrating that
# idea there. This script is actually here, to test the impact of such an idea and
# find first caveats and show-stoppers.
#
# Author: Kai Krakow <[email protected]>
# License: GPL3

file_already_queued = {}

IO.popen('xargs --no-run-if-empty --max-args=20 --max-procs=3 --null btrfs filesystem defragment -v -clzo', 'w') do |xargs|

  File.foreach('/var/lib/preload/preload.state') do |line|
    next unless %r{^(EXE|MAP)\s.*?file://(.*)} =~ line
    next if file_already_queued[name = $2]

    if File.exists?(name)
      xargs.print "#{name}\0"
      file_already_queued[name] = true
    end
  end

  xargs.flush

end