mm: stop kswapd's infinite loop at high order allocation

mm: stop kswapd's infinite loop at high order allocation

Wassim Dagash reported following kswapd infinite loop problem.

  kswapd runs in some infinite loop trying to swap until order 10 of zone
  highmem is OK.... kswapd will continue to try to balance order 10 of zone
  highmem forever (or until someone release a very large chunk of highmem).

For non order-0 allocations, the system may never be balanced due to
fragmentation but kswapd should not infinitely loop as a result.

Instead, recheck all watermarks at order-0 as they are the most important.
If watermarks are ok, kswapd will go back to sleep.

[[email protected]: fix comment]
Reported-by: wassim dagash <[email protected]>
Signed-off-by: KOSAKI Motohiro <[email protected]>
Reviewed-by: Nick Piggin <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>