vmscan: add newly swapped in pages to the inactive list

Swapin_readahead can read in a lot of data that the processes in memory
never need.  Adding swap cache pages to the inactive list prevents them
from putting too much pressure on the working set.

This has the potential to help the programs that are already in memory,
but it could also be a disadvantage to processes that are trying to get
swapped in.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>