[PATCH v2 4/5] mm/sparse-vmemmap: drop vmemmap_can_optimize()

[Muchun Song]

section_vmemmap_optimizable() can already decide whether a section uses
vmemmap optimization based on the section compound order. The DAX-specific
vmemmap_can_optimize() helper duplicates that policy, so remove it to
simplify the code.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
v2:
- Ignore non-optimizable nonzero section orders while retaining zero
  as the reset value (reported by Sashiko)
- Use section_vmemmap_optimization_disable() for the altmap fallback
- Move vmemmap_optimizable_order() before its first caller
---
 include/linux/mm.h                   | 37 ----------------------------
 include/linux/vmemmap-optimization.h | 25 ++++++++++---------
 mm/sparse-vmemmap.c                  |  6 +++--
 3 files changed, 18 insertions(+), 50 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a060a7150401..2fa5ce73b382 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -38,7 +38,6 @@
 #include <linux/bitops.h>
 #include <linux/iommu-debug-pagealloc.h>
 #include <linux/kcsan-checks.h>
-#include <linux/vmemmap-optimization.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -5366,42 +5365,6 @@ static inline void vmem_altmap_free(struct vmem_altmap *altmap,
 }
 #endif
 
-#ifdef CONFIG_ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
-static inline bool __vmemmap_can_optimize(struct vmem_altmap *altmap,
-					  struct dev_pagemap *pgmap)
-{
-	unsigned long nr_pages;
-	unsigned long nr_vmemmap_pages;
-
-	if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
-		return false;
-
-	if (!pgmap || !is_power_of_2(sizeof(struct page)))
-		return false;
-
-	nr_pages = pgmap_vmemmap_nr(pgmap);
-	nr_vmemmap_pages = ((nr_pages * sizeof(struct page)) >> PAGE_SHIFT);
-	/*
-	 * For vmemmap optimization with DAX we need minimum 2 vmemmap
-	 * pages. See layout diagram in Documentation/mm/vmemmap_dedup.rst
-	 */
-	return !altmap && (nr_vmemmap_pages > VMEMMAP_OPTIMIZATION_PAGES);
-}
-/*
- * If we don't have an architecture override, use the generic rule
- */
-#ifndef vmemmap_can_optimize
-#define vmemmap_can_optimize __vmemmap_can_optimize
-#endif
-
-#else
-static inline bool vmemmap_can_optimize(struct vmem_altmap *altmap,
-					   struct dev_pagemap *pgmap)
-{
-	return false;
-}
-#endif
-
 enum mf_flags {
 	MF_COUNT_INCREASED = 1 << 0,
 	MF_ACTION_REQUIRED = 1 << 1,
diff --git a/include/linux/vmemmap-optimization.h b/include/linux/vmemmap-optimization.h
index 5c09da4df4d8..9d9f7a67d195 100644
--- a/include/linux/vmemmap-optimization.h
+++ b/include/linux/vmemmap-optimization.h
@@ -31,6 +31,17 @@
 #define VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES	(VMEMMAP_OPTIMIZATION_SIZE / sizeof(struct page))
 #define VMEMMAP_OPTIMIZATION_MIN_ORDER		(ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1)
 
+static inline bool vmemmap_optimizable_order(unsigned int order)
+{
+	if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
+		return false;
+
+	if (!is_power_of_2(sizeof(struct page)))
+		return false;
+
+	return order >= VMEMMAP_OPTIMIZATION_MIN_ORDER;
+}
+
 #ifdef CONFIG_VMEMMAP_OPTIMIZATION
 static inline unsigned int section_compound_order(const struct mem_section *section)
 {
@@ -40,6 +51,9 @@ static inline unsigned int section_compound_order(const struct mem_section *sect
 static inline void section_set_compound_order(struct mem_section *section,
 					      unsigned int order)
 {
+	if (order && !vmemmap_optimizable_order(order))
+		return;
+
 	VM_WARN_ON(section_compound_order(section) && order &&
 		   section_compound_order(section) != order);
 	section->compound_page_order = order;
@@ -134,15 +148,4 @@ static inline bool vmemmap_optimizable_pfn(unsigned long pfn, unsigned int order
 
 	return (pfn & (nr_pages - 1)) >= VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES;
 }
-
-static inline bool vmemmap_optimizable_order(unsigned int order)
-{
-	if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
-		return false;
-
-	if (!is_power_of_2(sizeof(struct page)))
-		return false;
-
-	return order >= VMEMMAP_OPTIMIZATION_MIN_ORDER;
-}
 #endif /* _LINUX_VMEMMAP_OPTIMIZATION_H */
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index b8b55e12f5ba..71a927d67a9f 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -473,6 +473,9 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;
 
+	/* Altmap-backed vmemmap pages cannot be optimized. */
+	if (altmap)
+		section_vmemmap_optimization_disable(start, end);
 	r = vmemmap_populate(start, end, nid, altmap);
 	if (r < 0)
 		return NULL;
@@ -700,10 +703,9 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
 	struct mem_section *ms = __pfn_to_section(pfn);
 	struct mem_section_usage *usage = NULL;
 	struct page *memmap;
-	unsigned int order;
+	unsigned int order = pgmap ? pgmap->vmemmap_shift : 0;
 	int rc;
 
-	order = vmemmap_can_optimize(altmap, pgmap) ? pgmap->vmemmap_shift : 0;
 	if (nr_pages < PAGES_PER_SECTION && section_compound_order(ms))
 		return ERR_PTR(-EOPNOTSUPP);
 
-- 
2.54.0