Of course, that then makes shutdown take twice as long.
In most cases (no changes to the files since last shutdown), then a 'make' can shorten the latency to just a 'stat()' of each file. The whole computation can run in parallel with all other activities during shutdown, until just before the unmounts.
What do you do if you have a box where readahead makes boot slower?
Delete enough items from the list of filenames to be processed.