[PATCH 3/6] mm/mm_init.c: add new function calc_nr_kernel_pages()

[Baoquan He <bhe@redhat.com>]

This is a preparation to calculate nr_kernel_pages and nr_all_pages,
both of which will be used later in alloc_large_system_hash().

nr_all_pages counts up all free but not reserved memory in memblock
allocator, including HIGHMEM memory. While nr_kernel_pages counts up
all free but not reserved low memory in memblock allocator, excluding
HIGHMEM memory.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/mm_init.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 153fb2dc666f..c57a7fc97a16 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1264,6 +1264,30 @@ static void __init reset_memoryless_node_totalpages(struct pglist_data *pgdat)
 	pr_debug("On node %d totalpages: 0\n", pgdat->node_id);
 }
 
+static void __init calc_nr_kernel_pages(void)
+{
+	unsigned long start_pfn, end_pfn;
+	phys_addr_t start_addr, end_addr;
+	u64 u;
+#ifdef CONFIG_HIGHMEM
+	unsigned long high_zone_low = arch_zone_lowest_possible_pfn[ZONE_HIGHMEM];
+#endif
+
+	for_each_free_mem_range(u, NUMA_NO_NODE, MEMBLOCK_NONE, &start_addr, &end_addr, NULL) {
+		start_pfn = PFN_UP(start_addr);
+		end_pfn   = PFN_DOWN(end_addr);
+
+		if (start_pfn < end_pfn) {
+			nr_all_pages += end_pfn - start_pfn;
+#ifdef CONFIG_HIGHMEM
+			start_pfn = clamp(start_pfn, 0, high_zone_low);
+			end_pfn = clamp(end_pfn, 0, high_zone_low);
+#endif
+			nr_kernel_pages += end_pfn - start_pfn;
+		}
+	}
+}
+
 static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 						unsigned long node_start_pfn,
 						unsigned long node_end_pfn)
-- 
2.41.0