[PATCH 33/49] mm: introduce CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION

[Muchun Song]

Previously, the vmemmap optimization logic in mm/sparse-vmemmap.c was
closely tied to HugeTLB via CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP.
With recent refactoring (e.g., introducing compound page order to struct
mem_section), the core vmemmap optimization machinery has become more
generic and can be utilized by other subsystems like DAX.

To reflect this generalization and decouple the core optimization logic
from HugeTLB-specific configurations, this patch introduces a new common
Kconfig option: CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION.

Both HugeTLB and DAX now select this generic option, ensuring that the
shared optimization infrastructure is enabled whenever either subsystem
requires it.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
 fs/Kconfig                 |  1 +
 include/linux/mmzone.h     | 33 ++++++++++++++++++---------------
 include/linux/page-flags.h |  5 +----
 mm/Kconfig                 |  5 +++++
 4 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index e70aa5f0429a..9b56a90e13db 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -278,6 +278,7 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	def_bool HUGETLB_PAGE
 	depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	depends on SPARSEMEM_VMEMMAP
+	select SPARSEMEM_VMEMMAP_OPTIMIZATION
 
 config HUGETLB_PMD_PAGE_TABLE_SHARING
 	def_bool HUGETLB_PAGE
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 75425407e0c4..6edcb0cc46c4 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -102,9 +102,9 @@
  *
  * HVO which is only active if the size of struct page is a power of 2.
  */
-#define MAX_FOLIO_VMEMMAP_ALIGN \
-	(IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && \
-	 is_power_of_2(sizeof(struct page)) ? \
+#define MAX_FOLIO_VMEMMAP_ALIGN					\
+	(IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION) &&	\
+	 is_power_of_2(sizeof(struct page)) ?			\
 	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
 
 /* The number of vmemmap pages required by a vmemmap-optimized folio. */
@@ -115,7 +115,8 @@
 
 #define __NR_OPTIMIZABLE_FOLIO_SIZES		(MAX_FOLIO_ORDER - OPTIMIZABLE_FOLIO_MIN_ORDER + 1)
 #define NR_OPTIMIZABLE_FOLIO_SIZES		\
-	(__NR_OPTIMIZABLE_FOLIO_SIZES > 0 ? __NR_OPTIMIZABLE_FOLIO_SIZES : 0)
+	((__NR_OPTIMIZABLE_FOLIO_SIZES > 0 &&	\
+	  IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION)) ? __NR_OPTIMIZABLE_FOLIO_SIZES : 0)
 
 enum migratetype {
 	MIGRATE_UNMOVABLE,
@@ -2014,7 +2015,7 @@ struct mem_section {
 	 */
 	struct page_ext *page_ext;
 #endif
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
 	/*
 	 * The order of compound pages in this section. Typically, the section
 	 * holds compound pages of this order; a larger compound page will span
@@ -2194,7 +2195,19 @@ static inline bool pfn_section_first_valid(struct mem_section *ms, unsigned long
 	*pfn = (*pfn & PAGE_SECTION_MASK) + (bit * PAGES_PER_SUBSECTION);
 	return true;
 }
+#else
+static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
+{
+	return 1;
+}
+
+static inline bool pfn_section_first_valid(struct mem_section *ms, unsigned long *pfn)
+{
+	return true;
+}
+#endif
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
 static inline void section_set_order(struct mem_section *section, unsigned int order)
 {
 	VM_BUG_ON(section->order && order && section->order != order);
@@ -2206,16 +2219,6 @@ static inline unsigned int section_order(const struct mem_section *section)
 	return section->order;
 }
 #else
-static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
-{
-	return 1;
-}
-
-static inline bool pfn_section_first_valid(struct mem_section *ms, unsigned long *pfn)
-{
-	return true;
-}
-
 static inline void section_set_order(struct mem_section *section, unsigned int order)
 {
 }
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0e03d816e8b9..12665b34586c 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -208,14 +208,11 @@ enum pageflags {
 static __always_inline bool compound_info_has_mask(void)
 {
 	/*
-	 * Limit mask usage to HugeTLB vmemmap optimization (HVO) where it
-	 * makes a difference.
-	 *
 	 * The approach with mask would work in the wider set of conditions,
 	 * but it requires validating that struct pages are naturally aligned
 	 * for all orders up to the MAX_FOLIO_ORDER, which can be tricky.
 	 */
-	if (!IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP))
+	if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
 		return false;
 
 	return is_power_of_2(sizeof(struct page));
diff --git a/mm/Kconfig b/mm/Kconfig
index 3cce862088f1..e81aa77182b2 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -410,12 +410,17 @@ config SPARSEMEM_VMEMMAP
 	  pfn_to_page and page_to_pfn operations.  This is the most
 	  efficient option when sufficient kernel resources are available.
 
+config SPARSEMEM_VMEMMAP_OPTIMIZATION
+	bool
+	depends on SPARSEMEM_VMEMMAP
+
 #
 # Select this config option from the architecture Kconfig, if it is preferred
 # to enable the feature of HugeTLB/dev_dax vmemmap optimization.
 #
 config ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
 	bool
+	select SPARSEMEM_VMEMMAP_OPTIMIZATION if SPARSEMEM_VMEMMAP
 
 config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	bool
-- 
2.20.1