Can we make readahead more robust to package updates?

[John Reiser]

> 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.

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