The present method should be reading sequentially (with gaps),
rather than randomly. Perhaps we need to check what's happening
in practice.
(I've often dithered over whether we should be doing swap readahead
there or not: at present it does not, preferring to assume buffering
at the hardware level, and last time I checked that worked out a
little better.)
(I didn't understand your point there, but Daniel has replied that
it's not at shutdown anyway.)
We definitely don't page those in, it would be a disaster for process
exit if we did: they just get discarded.
As you say, shutdown is rarely a big issue, because almost all the
processes which had stuff in swap have already been killed. tmpfs
use of swap can be an issue there, but if the distro is wise, it'll
do things in such an order that tmpfs'es are unmounted before swapoff
(but may need two passes: the opposite case is a regular swapfile,
where we need to swapoff before that partition can be unmounted).
Hugh
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