[PATCH] sparsemem base: early_pfn_to_nid() (works before sparse is initialized)

The following four patches provide the last needed changes before the
introduction of sparsemem.  For a more complete description of what this
will do, please see this patch:

http://www.sr71.net/patches/2.6.11/2.6.11-bk7-mhp1/broken-out/B-sparse-150-sparsemem.patch

or previous posts on the subject:
http://marc.theaimsgroup.com/?t=110868540700001&r=1&w=2
http://marc.theaimsgroup.com/?l=linux-mm&m=109897373315016&w=2

Three of these are i386-only, but one of them reorganizes the macros
used to manage the space in page->flags, and will affect all platforms.
There are analogous patches to the i386 ones for ppc64, ia64, and
x86_64, but those will be submitted by the normal arch maintainers.

The combination of the four patches has been test-booted on a variety of
i386 hardware, and compiled for ppc64, i386, and x86-64 with about 17
different .configs.  It's also been runtime-tested on ia64 configs (with
more patches on top).

This patch:

We _know_ which node pages in general belong to, at least at a very gross
level in node_{start,end}_pfn[].  Use those to target the allocations of
pages.
Signed-off-by: NAndy Whitcroft <apw@shadowen.org>
Signed-off-by: NDave Hansen <haveblue@us.ibm.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/i386/mm/discontig.c

@@ -146,6 +146,21 @@ static void __init find_max_pfn_node(int nid)
 		BUG();
 }
 
+/* Find the owning node for a pfn. */
+int early_pfn_to_nid(unsigned long pfn)
+{
+	int nid;
+
+	for_each_node(nid) {
+		if (node_end_pfn[nid] == 0)
+			break;
+		if (node_start_pfn[nid] <= pfn && node_end_pfn[nid] >= pfn)
+			return nid;
+	}
+
+	return 0;
+}
+
 /* 
  * Allocate memory for the pg_data_t for this node via a crude pre-bootmem
  * method.  For node zero take this from the bottom of memory, for