We've been futzing with the scan rates of the inactive and active lists far
too much, and it's still not right (Anton reports interrupt-off times of over
a second).

- We have this logic in there from 2.4.early (at least) which tries to keep
  the inactive list 1/3rd the size of the active list.  Or something.

  I really cannot see any logic behind this, so toss it out and change the
  arithmetic in there so that all pages on both lists have equal scan rates.

- Chunk the work up so we never hold interrupts off for more that 32 pages
  worth of scanning.

- Make the per-zone scan-count accumulators unsigned long rather than
  atomic_t.

  Mainly because atomic_t's could conceivably overflow, but also because
  access to these counters is racy-by-design anyway.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>