1 files changed, 54 insertions, 0 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4e8985acdab8..9119faae6e6a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4585,6 +4585,60 @@ void __init sort_node_map(void)
 			cmp_node_active_region, NULL);
 }
 
+/**
+ * node_map_pfn_alignment - determine the maximum internode alignment
+ *
+ * This function should be called after node map is populated and sorted.
+ * It calculates the maximum power of two alignment which can distinguish
+ * all the nodes.
+ *
+ * For example, if all nodes are 1GiB and aligned to 1GiB, the return value
+ * would indicate 1GiB alignment with (1 << (30 - PAGE_SHIFT)).  If the
+ * nodes are shifted by 256MiB, 256MiB.  Note that if only the last node is
+ * shifted, 1GiB is enough and this function will indicate so.
+ *
+ * This is used to test whether pfn -> nid mapping of the chosen memory
+ * model has fine enough granularity to avoid incorrect mapping for the
+ * populated node map.
+ *
+ * Returns the determined alignment in pfn's.  0 if there is no alignment
+ * requirement (single node).
+ */
+unsigned long __init node_map_pfn_alignment(void)
+{
+	unsigned long accl_mask = 0, last_end = 0;
+	int last_nid = -1;
+	int i;
+
+	for_each_active_range_index_in_nid(i, MAX_NUMNODES) {
+		int nid = early_node_map[i].nid;
+		unsigned long start = early_node_map[i].start_pfn;
+		unsigned long end = early_node_map[i].end_pfn;
+		unsigned long mask;
+
+		if (!start || last_nid < 0 || last_nid == nid) {
+			last_nid = nid;
+			last_end = end;
+			continue;
+		}
+
+		/*
+		 * Start with a mask granular enough to pin-point to the
+		 * start pfn and tick off bits one-by-one until it becomes
+		 * too coarse to separate the current node from the last.
+		 */
+		mask = ~((1 << __ffs(start)) - 1);
+		while (mask && last_end <= (start & (mask << 1)))
+			mask <<= 1;
+
+		/* accumulate all internode masks */
+		accl_mask |= mask;
+	}
+
+	/* convert mask to number of pages */
+	return ~accl_mask + 1;
+}
+
 /* Find the lowest pfn for a node */
 static unsigned long __init find_min_pfn_for_node(int nid)
 {