Currently we keep track of a pages node & zone in the top 8 bits (on 
32-bit arches, 10 bits on 64-bit arches) of page->flags.  We typically 
do: node_num * MAX_NR_ZONES + zone_num = 'nodezone'.  It's non-trivial 
to break this 'nodezone' back into node and zone numbers.  This patch 
modifies the way we compute the index to be: (node_num << ZONE_SHIFT) | 
zone_num.  This makes it trivial to recover either the node or zone 
number with a simple bitshift.  There are many places in the kernel 
where we do things like: page_zone(page)->zone_pgdat->node_id to 
determine the node a page belongs to.  With this patch we save several 
pointer dereferences, and it boils down to shifting some bits.

Comments/criticism requested.

[mcd@arrakis current]$ diffstat nodezone.patch
  include/linux/mm.h     |   21 ++++++++++++++++-----
  include/linux/mmzone.h |   15 ++++++++++++---
  mm/page_alloc.c        |    6 +++---
  3 files changed, 31 insertions(+), 11 deletions(-)

Cheers!

-Matt