[PATCH 3/4] 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>
---
 include/linux/mm.h  | 37 -------------------------------------
 mm/sparse-vmemmap.c | 11 +++++++++--
 2 files changed, 9 insertions(+), 39 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e875f73b0c6f..4fb48fbe712d 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;
@@ -5395,42 +5394,6 @@ 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/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 3e9d6617c4bb..43559593107c 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -466,12 +466,20 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 {
 	unsigned long start = (unsigned long) pfn_to_page(pfn);
 	unsigned long end = start + nr_pages * sizeof(struct page);
+	struct mem_section *ms = __pfn_to_section(pfn);
 	int r;
 
 	if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) ||
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;
 
+	/*
+	 * Vmemmap optimization is not supported when vmemmap pages are backed
+	 * by an altmap.
+	 */
+	if (altmap && section_vmemmap_optimizable(ms))
+		section_set_compound_order(ms, 0);
+
 	r = vmemmap_populate(start, end, nid, altmap);
 	if (r < 0)
 		return NULL;
@@ -699,10 +707,9 @@ 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