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 
compute the field as follows:
	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 all boils down to shifting some bits.

Cheers!

-Matt