Re: [RFC] Simplify node/zone portion of page->flags

[Andrew Morton]

Matthew Dobson <colpatch@xxxxxxxxxx> wrote:
>
> 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.

This rather conflicts with the patch from Jesse which I have.  Can you guys
work that out and let me know when you're done?

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