+ mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch added to mm-new branch

+ mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/sparse-vmemmap: drop Device DAX-specific population path
has been added to the -mm mm-new branch.  Its filename is
     mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: mm/sparse-vmemmap: drop Device DAX-specific population path
Date: Tue, 29 Sep 2026 13:32:28 +0800

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.

Link: https://lore.kernel.org/20260929053231.66085-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <chleroy@kernel.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
---

 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(-)

--- a/arch/powerpc/mm/book3s64/radix_pgtable.c~mm-sparse-vmemmap-drop-device-dax-specific-population-path
+++ a/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -1122,7 +1122,10 @@ int __meminit radix__vmemmap_populate(un
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;
+	unsigned long pfn = page_to_pfn((struct page *)start);
 
+	if (vmemmap_optimizable_order(pfn_to_section_compound_order(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
--- a/mm/mm_init.c~mm-sparse-vmemmap-drop-device-dax-specific-population-path
+++ a/mm/mm_init.c
@@ -1046,7 +1046,7 @@ static void zone_device_page_init_from_t
  * 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)
--- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-drop-device-dax-specific-population-path
+++ a/mm/sparse-vmemmap.c
@@ -499,71 +499,6 @@ int __meminit vmemmap_populate_hugepages
 	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)
@@ -576,11 +511,7 @@ struct page * __meminit __populate_secti
 		!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;
 
_

Patches currently in -mm which might be from muchun.song@linux.dev are

mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch
mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch
mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch
mm-sparse-vmemmap-open-code-init_compound_tail.patch
mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch
mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch
mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch
powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch
mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch
documentation-mm-update-dax-vmemmap-deduplication-docs.patch
mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch
mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch
mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch
mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch
mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch
mm-mm_init-add-zone-mismatch-warning-during-page-init.patch