"It has been almost two years since LWN covered the swap
prefetch patch. This work, done by Con Kolivas, is based on the
idea that if a system is idle, and it has pushed user data out to
swap, perhaps it should spend a little time speculatively fetching
that swapped data back into any free memory that might be sitting
around. Then, when some application wants that memory in the
future, it will already be available and the time-consuming process
of fetching it from disk can be avoided.
"The classic use case for this feature is a desktop system which
runs memory-intensive daemons (updatedb, say, or a backup process)
during the night..."