mm: remove swap token code

mm: remove swap token code

The swap token code no longer fits in with the current VM model.  It does
not play well with cgroups or the better NUMA placement code in
development, since we have only one swap token globally.

It also has the potential to mess with scalability of the system, by
increasing the number of non-reclaimable pages on the active and inactive
anon LRU lists.

Last but not least, the swap token code has been broken for a year without
complaints, as reported by Konstantin Khlebnikov.  This suggests we no
longer have much use for it.

The days of sub-1G memory systems with heavy use of swap are over.  If we
ever need thrashing reducing code in the future, we will have to implement
something that does scale.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>