swap_info and swap_map patches

Here's a series of nine patches around the swap_info_struct: against
2.6.32-rc4, but intended for mmotm, which is currently similar here.

They start out with some old and not very important cleanups, but get
around to solving the swap count overflow problem: our handling above
32765 has depended on hoping that it won't coincide with other races.

That problem exists in theory today (when pid_max is raised from its
default), though never reported in practice; but the motivation for
solving it now comes from the impending KSM swapping patches - it
becomes very easy for anyone to overflow the maximum that way.

But most people will never have a swap count overflow in their life:
the benefit for them is that the vmalloc'ed swap_map halves in size.

This is all internal housekeeping: no change to actual swapping and
page reclaim.

 include/linux/swap.h |   66 ++-
 mm/memory.c          |   19 
 mm/page_io.c         |   19 
 mm/rmap.c            |    6 
 mm/shmem.c           |   11 
 mm/swapfile.c        |  834 +++++++++++++++++++++++++----------------
 6 files changed, 599 insertions(+), 356 deletions(-)

Hugh

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