This is the fixup of the zone reclaim logic that we discussed at
http://marc.theaimsgroup.com/?t=113632936900003&r=1&w=2

This patchset is against 2.6.15-git6.

First patch restores may_swap in vmscan.c as it was in 2.6.15.

The second patch restores the zone_reclaim function and has core logic
that was already discussed. Also removes yet another leftover definition
from Martin Hicks reclaim in struct zone.

The third patch introduces /proc/sys/vm/zone_reclaim_mode that allows
the overriding of the determination of the zone reclaim mode on bootup.

Zone reclaim has a huge impact on NUMA performance (f.e. our maximum throughput with XFS
is raised from 4GB to 6GB/sec / page cache contamination of numa nodes destroys locality
if one just does a large copy operation which results in performance dropping for good
until reboot).

That is why we had Ray Bryant and Martin Hicks work on this for the last year and
the code was extensively discussed.

Could this also go into 2.6.16?