[PATCHv3 01/13] mm, sparsemem: Allocate mem_section at runtime for SPARSEMEM_EXTREME

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Size of mem_section array depends on size of physical address space.

In preparation for boot-time switching between paging modes on x86-64
we need to make allocation of mem_section dynamic.

The patch allocates the array on the first call to
sparse_memory_present_with_active_regions().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 include/linux/mmzone.h |  2 +-
 mm/page_alloc.c        | 10 ++++++++++
 mm/sparse.c            |  3 +--
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index fc14b8b3f6ce..c8eb668eab79 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1137,7 +1137,7 @@ struct mem_section {
 #define SECTION_ROOT_MASK	(SECTIONS_PER_ROOT - 1)
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
-extern struct mem_section *mem_section[NR_SECTION_ROOTS];
+extern struct mem_section **mem_section;
 #else
 extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
 #endif
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6d30e914afb6..639fd2dce0c4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5681,6 +5681,16 @@ void __init sparse_memory_present_with_active_regions(int nid)
 	unsigned long start_pfn, end_pfn;
 	int i, this_nid;
 
+#ifdef CONFIG_SPARSEMEM_EXTREME
+	if (!mem_section) {
+		unsigned long size, align;
+
+		size = sizeof(struct mem_section) * NR_SECTION_ROOTS;
+		align = 1 << (INTERNODE_CACHE_SHIFT);
+		mem_section = memblock_virt_alloc(size, align);
+	}
+#endif
+
 	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, &this_nid)
 		memory_present(this_nid, start_pfn, end_pfn);
 }
diff --git a/mm/sparse.c b/mm/sparse.c
index 7b4be3fd5cac..3a226a8c1968 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -22,8 +22,7 @@
  * 1) mem_section	- memory sections, mem_map's for valid memory
  */
 #ifdef CONFIG_SPARSEMEM_EXTREME
-struct mem_section *mem_section[NR_SECTION_ROOTS]
-	____cacheline_internodealigned_in_smp;
+struct mem_section **mem_section;
 #else
 struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT]
 	____cacheline_internodealigned_in_smp;
-- 
2.13.2