Initialize the node's memory-regions structures with the information about
the region-boundaries, at boot time.

Based-on-patch-by: Ankita Garg <gargank...@gmail.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 include/linux/mm.h |    4 ++++
 mm/page_alloc.c    |   28 ++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f022460..18fdec4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -627,6 +627,10 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct 
vm_area_struct *vma)
 #define LAST_NID_MASK          ((1UL << LAST_NID_WIDTH) - 1)
 #define ZONEID_MASK            ((1UL << ZONEID_SHIFT) - 1)
 
+/* Hard-code memory region size to be 512 MB for now. */
+#define MEM_REGION_SHIFT       (29 - PAGE_SHIFT)
+#define MEM_REGION_SIZE                (1UL << MEM_REGION_SHIFT)
+
 static inline enum zone_type page_zonenum(const struct page *page)
 {
        return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b86d7e3..bb2d5d4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4809,6 +4809,33 @@ static void __init_refok alloc_node_mem_map(struct 
pglist_data *pgdat)
 #endif /* CONFIG_FLAT_NODE_MEM_MAP */
 }
 
+static void __meminit init_node_memory_regions(struct pglist_data *pgdat)
+{
+       int nid = pgdat->node_id;
+       unsigned long start_pfn = pgdat->node_start_pfn;
+       unsigned long end_pfn = start_pfn + pgdat->node_spanned_pages;
+       struct node_mem_region *region;
+       unsigned long i, absent;
+       int idx;
+
+       for (i = start_pfn, idx = 0; i < end_pfn;
+                               i += region->spanned_pages, idx++) {
+
+               region = &pgdat->node_regions[idx];
+               region->pgdat = pgdat;
+               region->start_pfn = i;
+               region->spanned_pages = min(MEM_REGION_SIZE, end_pfn - i);
+               region->end_pfn = region->start_pfn + region->spanned_pages;
+
+               absent = __absent_pages_in_range(nid, region->start_pfn,
+                                                region->end_pfn);
+
+               region->present_pages = region->spanned_pages - absent;
+       }
+
+       pgdat->nr_node_regions = idx;
+}
+
 void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
                unsigned long node_start_pfn, unsigned long *zholes_size)
 {
@@ -4837,6 +4864,7 @@ void __paginginit free_area_init_node(int nid, unsigned 
long *zones_size,
 
        free_area_init_core(pgdat, start_pfn, end_pfn,
                            zones_size, zholes_size);
+       init_node_memory_regions(pgdat);
 }
 
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP

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