[PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case

[Baoquan He]

Currently, subsection map is used when SPARSEMEM is enabled, including
VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not
supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary
and misleading. Let's adjust code to only allow subsection map being
used in VMEMMAP case.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
 include/linux/mmzone.h |  2 ++
 mm/sparse.c            | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 462f6873905a..fc0de3a9a51e 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1185,7 +1185,9 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
 #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)
 
 struct mem_section_usage {
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
 	DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
+#endif
 	/* See declaration of similar field in struct zone */
 	unsigned long pageblock_flags[0];
 };
diff --git a/mm/sparse.c b/mm/sparse.c
index df857ee9330c..66c497d6a229 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -209,6 +209,7 @@ static inline unsigned long first_present_section_nr(void)
 	return next_present_section_nr(-1);
 }
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
 static void subsection_mask_set(unsigned long *map, unsigned long pfn,
 		unsigned long nr_pages)
 {
@@ -243,6 +244,11 @@ void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
 		nr_pages -= pfns;
 	}
 }
+#else
+void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages)
+{
+}
+#endif
 
 /* Record a memory area against a node. */
 void __init memory_present(int nid, unsigned long start, unsigned long end)
@@ -726,6 +732,7 @@ static void free_map_bootmem(struct page *memmap)
 }
 #endif /* CONFIG_SPARSEMEM_VMEMMAP */
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
 /**
  * clear_subsection_map - Clear subsection map of one memory region
  *
@@ -764,6 +771,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
 
 	return 1;
 }
+#else
+static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages)
+{
+	return 0;
+}
+#endif
 
 static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
 		struct vmem_altmap *altmap)
@@ -820,6 +833,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
 		ms->section_mem_map = (unsigned long)NULL;
 }
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
 /**
  * fill_subsection_map - fill subsection map of a memory region
  * @pfn - start pfn of the memory range
@@ -854,6 +868,12 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
 
 	return rc;
 }
+#else
+static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages)
+{
+	return 0;
+}
+#endif
 
 static struct page * __meminit section_activate(int nid, unsigned long pfn,
 		unsigned long nr_pages, struct vmem_altmap *altmap)
-- 
2.17.2