2.4: why is NR_GFPINDEX so large?

[Timur Tabi <ttabi@interactivesi.com>]

In mmzone.h, NR_GFPINDEX is set to 0x100.  This means that the node_zonelists
array in pg_data_t has 256 elements.  However, then we have code like this in
mm.h:

static inline struct page * alloc_pages(int gfp_mask, unsigned long order)
{
[snip]
	return __alloc_pages(contig_page_data.node_zonelists+(gfp_mask), order);
}

gfp_mask is any combination of any of these flags (from mm.h):

#define __GFP_WAIT	0x01
#define __GFP_HIGH	0x02
#define __GFP_IO	0x04
#define __GFP_DMA	0x08
#define __GFP_HIGHMEM	0x10

Which means theorectically, the largest value is 0x1F, or 31.  This means that
elements 32-255 of array node_zonelists are never accessed.  Can someone explain
this to me?



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Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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