[PATCH 3/6] mm/sparse-vmemmap: drop Device DAX-specific population path

[Muchun Song]

The common vmemmap path selects the shared page for optimized mappings
itself, so Device DAX no longer needs vmemmap_populate_compound_pages()
to find a shared tail page and pass its backing PFN through the generic
population helpers.

Remove the Device DAX-specific population path and let section memmap
population always use vmemmap_populate(). The powerpc retains an
architecture-specific compound-page implementation, so select it directly
from radix__vmemmap_populate() for optimizable sections.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 arch/powerpc/mm/book3s64/radix_pgtable.c |  3 +
 mm/mm_init.c                             |  2 +-
 mm/sparse-vmemmap.c                      | 71 +-----------------------
 3 files changed, 5 insertions(+), 71 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 9ca28e4a610a..cb72d9ccf747 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -1122,7 +1122,10 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
+	unsigned long pfn = page_to_pfn((struct page *)start);
 
+	if (section_vmemmap_optimizable(__pfn_to_section(pfn)))
+		return vmemmap_populate_compound_pages(pfn, start, end, node, NULL);
 	/*
 	 * If altmap is present, Make sure we align the start vmemmap addr
 	 * to PAGE_SIZE so that we calculate the correct start_pfn in
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 56bb4567a494..1650d6bc1211 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1046,7 +1046,7 @@ static void zone_device_page_init_from_template(struct page *page,
  * initialize is a lot smaller that the total amount of struct pages being
  * mapped. This is a paired / mild layering violation with explicit knowledge
  * of how the sparse_vmemmap internals handle compound pages in the lack
- * of an altmap. See vmemmap_populate_compound_pages().
+ * of an altmap.
  */
 static inline unsigned long compound_nr_pages(unsigned long pfn,
 					      struct dev_pagemap *pgmap)
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index e83821768c12..028f844c90f5 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -454,71 +454,6 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
 	return 0;
 }
 
-#ifndef vmemmap_populate_compound_pages
-/*
- * For compound pages bigger than section size (e.g. x86 1G compound
- * pages with 2M subsection size) fill the rest of sections as tail
- * pages.
- *
- * Note that memremap_pages() resets @nr_range value and will increment
- * it after each range successful onlining. Thus the value or @nr_range
- * at section memmap populate corresponds to the in-progress range
- * being onlined here.
- */
-static bool __meminit reuse_compound_section(unsigned long start_pfn,
-					     struct dev_pagemap *pgmap)
-{
-	unsigned long nr_pages = pgmap_vmemmap_nr(pgmap);
-	unsigned long offset = start_pfn -
-		PHYS_PFN(pgmap->ranges[pgmap->nr_range].start);
-
-	return !IS_ALIGNED(offset, nr_pages) && nr_pages > PAGES_PER_SUBSECTION;
-}
-
-static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
-						     unsigned long start,
-						     unsigned long end, int node,
-						     struct dev_pagemap *pgmap)
-{
-	unsigned long size, addr;
-	pte_t *pte;
-	int rc;
-	struct page *page;
-	unsigned int order = pfn_to_section_compound_order(start_pfn);
-
-	page = vmemmap_shared_tail_page(order, device_zone(node));
-	if (!page)
-		return -ENOMEM;
-
-	if (reuse_compound_section(start_pfn, pgmap))
-		return vmemmap_populate_range(start, end, node, NULL,
-					      page_to_pfn(page));
-
-	size = min(end - start, (1UL << order) * sizeof(struct page));
-	for (addr = start; addr < end; addr += size) {
-		unsigned long next, last = addr + size;
-
-		/* Populate the head page vmemmap page */
-		pte = vmemmap_populate_address(addr, node, NULL, -1);
-		if (!pte)
-			return -ENOMEM;
-
-		/*
-		 * Reuse the shared page for the rest of tail pages
-		 * See layout diagram in Documentation/mm/vmemmap_dedup.rst
-		 */
-		next = addr + PAGE_SIZE;
-		rc = vmemmap_populate_range(next, last, node, NULL,
-					    page_to_pfn(page));
-		if (rc)
-			return -ENOMEM;
-	}
-
-	return 0;
-}
-
-#endif
-
 struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
 		struct dev_pagemap *pgmap)
@@ -531,11 +466,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;
 
-	if (pgmap && section_vmemmap_optimizable(__pfn_to_section(pfn)))
-		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
-	else
-		r = vmemmap_populate(start, end, nid, altmap);
-
+	r = vmemmap_populate(start, end, nid, altmap);
 	if (r < 0)
 		return NULL;
 
-- 
2.54.0