Re: [PATCH] Get rid of zone_table V2

[Christoph Lameter <clameter@sgi.com>]

On Mon, 18 Sep 2006, Andrew Morton wrote:

> > We avoid one memory reference for SMP and UP and do an address calculation
> > instead.
> 
> What memory reference do we avoid?  zone_table?

Yes.
 
> In exchange for that we've added an additional deref of page->flags and a
> new read from contig_page_data.

The additional deref of page->flags is the same as before. The compiler 
optimizes that one away. We need to extract two sets of bits from the same
register.

> > NODE_DATA() is constant for the UP and SMP case.
> 
> setenv ARCH i386
> make allnoconfig
> make mm/page_alloc.i
> grep contig_page_data mm/page_alloc.i
> 
> and that's mainline.  Changing page_zone to also read from contig_page_data
> will presumably worsen things.

Hmmm... I have not checked i386 code generation.
But include/linux/mmzone.h has

extern struct pglist_data contig_page_data;
#define NODE_DATA(nid)          (&contig_page_data)

So we should have an address there on SMP/UP.

NODE_DATA(nid0->node_zones == contig_page_data.node_zones

which I thought would still be constant. Then we calculate the address of 
the ith element of node_zones.


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