mempolicies: fix policy_zone check

There is a check in zonelist_policy that compares the bitmap obtained
from the gfp mask by an AND with GFP_ZONETYPES with a zone number.

The bitmaps is an ORed mask of __GFP_DMA, __GFP_DMA32 and __GFP_HIGHMEM.
The policy_zone is a zone number with the possible values of ZONE_DMA,
ZONE_DMA32, ZONE_HIGHMEM and ZONE_NORMAL.
These are two different domains of values.

For some reason this worked before (mostly??) when we always had 4 zones.
With the zone reduction patchset this check fails on systems with only ZONE_DMA
and ZONE_NORMAL if the system actually has memory in both zones.

This is because ZONE_NORMAL is selected using no __GFP flag at
all (and thus gfp_zone(...) == 0).
ZONE_DMA is selected when __GFP_DMA is set. __GFP_DMA is 0x01. 

policy_zone is set to ZONE_NORMAL (==1) if ZONE_NORMAL and ZONE_DMA are
populated.

gfp_zone(<no _GFP_DMA>) yields 0 which is < ZONE_NORMAL and so policy is not
applied to regular memory allocations!

Instead gfp_zone(__GFP_DMA) == 1 which results in policy being applied
to DMA allocations!

What we realy want in that place is to establish the highest allowable
zone for a given gfp_mask. If the highest zone is higher or equal to the
policy_zone then memory policies need to be applied. We have such
a highest_zone() function in page_alloc.c.

So move the highest_zone() function from mm/page_alloc.c into
include/linux/gfp.h.  On the way we simplify the function and use the new
zone_type that was also introduced with the zone reduction patchset plus we
also specify the right type for the gfp flags parameter.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by:  Lee Schermerhorn <Lee.Schermerhorn@hp.com>

Index: test/mm/mempolicy.c
===================================================================
--- test.orig/mm/mempolicy.c	2006-07-15 14:53:08.000000000 -0700
+++ test/mm/mempolicy.c	2006-08-04 12:31:17.000000000 -0700
@@ -1096,7 +1096,7 @@
 	case MPOL_BIND:
 		/* Lower zones don't get a policy applied */
 		/* Careful: current->mems_allowed might have moved */
-		if (gfp_zone(gfp) >= policy_zone)
+		if (highest_zone(gfp) >= policy_zone)
 			if (cpuset_zonelist_valid_mems_allowed(policy->v.zonelist))
 				return policy->v.zonelist;
 		/*FALL THROUGH*/
Index: test/include/linux/gfp.h
===================================================================
--- test.orig/include/linux/gfp.h	2006-08-04 12:16:03.000000000 -0700
+++ test/include/linux/gfp.h	2006-08-04 12:31:14.000000000 -0700
@@ -85,6 +85,21 @@
 	return zone;
 }
 
+static inline enum zone_type highest_zone(gfp_t flags)
+{
+	if (flags & __GFP_DMA)
+		return ZONE_DMA;
+#ifdef CONFIG_ZONE_DMA32
+	if (flags & __GFP_DMA32)
+		return ZONE_DMA32;
+#endif
+#ifdef CONFIG_HIGHMEM
+	if (flags & __GFP_HIGHMEM)
+		return ZONE_HIGHMEM;
+#endif
+	return ZONE_NORMAL;
+}
+
 /*
  * There is only one page-allocator function, and two main namespaces to
  * it. The alloc_page*() variants return 'struct page *' and as such
Index: test/mm/page_alloc.c
===================================================================
--- test.orig/mm/page_alloc.c	2006-08-04 12:16:13.000000000 -0700
+++ test/mm/page_alloc.c	2006-08-04 12:55:21.000000000 -0700
@@ -1466,22 +1466,6 @@
 	return nr_zones;
 }
 
-static inline int highest_zone(int zone_bits)
-{
-	int res = ZONE_NORMAL;
-#ifdef CONFIG_HIGHMEM
-	if (zone_bits & (__force int)__GFP_HIGHMEM)
-		res = ZONE_HIGHMEM;
-#endif
-#ifdef CONFIG_ZONE_DMA32
-	if (zone_bits & (__force int)__GFP_DMA32)
-		res = ZONE_DMA32;
-#endif
-	if (zone_bits & (__force int)__GFP_DMA)
-		res = ZONE_DMA;
-	return res;
-}
-
 #ifdef CONFIG_NUMA
 #define MAX_NODE_LOAD (num_online_nodes())
 static int __meminitdata node_load[MAX_NUMNODES];