[PATCH] shrink_all_memory() fixes

[PATCH] shrink_all_memory() fixes

- Off-by-one in balance_pgdat means that we're not scanning the zones all
  the way down to priority=0.

- Always set zone->temp_priority in shrink_caches().  I'm not sure why I had
  the `if (zone->free_pages < zone->pages_high)' test in there, but it's
  preventing us from setting ->prev_priority correctly on the
  try_to_free_pages() path.

- Set zone->prev_priority to the current priority if it's currently a
  "lower" priority.  This allows us to build up the pressure on mapped pages
  on the first scanning pass rather than only on successive passes.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>