+ mm-sparse-vmemmap-open-code-init_compound_tail.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/sparse-vmemmap: open-code init_compound_tail()
has been added to the -mm mm-new branch.  Its filename is
     mm-sparse-vmemmap-open-code-init_compound_tail.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-open-code-init_compound_tail.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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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm/sparse-vmemmap: open-code init_compound_tail()
Date: Fri, 11 Sep 2026 13:02:20 +0800

init_compound_tail() is only used by vmemmap_shared_tail_page(), where the
shared tail page setup intentionally passes NULL as the compound head.

Keeping this helper in mm/internal.h exposes that special case to the rest
of the MM code and can make the NULL head argument look generally valid. 
Open-code the initialization at the only call site so the special-case use
stays local to sparse vmemmap optimization.

No functional change intended.

Link: https://lore.kernel.org/20260911050228.58884-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/internal.h       |    9 ---------
 mm/sparse-vmemmap.c |    5 ++++-
 2 files changed, 4 insertions(+), 10 deletions(-)

--- a/mm/internal.h~mm-sparse-vmemmap-open-code-init_compound_tail
+++ a/mm/internal.h
@@ -786,15 +786,6 @@ static inline void prep_compound_tail(st
 	VM_WARN_ON_ONCE(tail->private);
 }
 
-static inline void init_compound_tail(struct page *tail,
-		const struct page *head, unsigned int order, struct zone *zone)
-{
-	atomic_set(&tail->_mapcount, -1);
-	set_page_node(tail, zone_to_nid(zone));
-	set_page_zone(tail, zone_idx(zone));
-	prep_compound_tail(tail, head, order);
-}
-
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
 
 /*
--- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-open-code-init_compound_tail
+++ a/mm/sparse-vmemmap.c
@@ -189,7 +189,10 @@ struct page __ref *vmemmap_shared_tail_p
 	for (int i = 0; i < PAGE_SIZE / sizeof(struct page); i++) {
 		page = (struct page *)addr + i;
 		mm_zero_struct_page(page);
-		init_compound_tail(page, NULL, order, zone);
+		atomic_set(&page->_mapcount, -1);
+		set_page_node(page, zone_to_nid(zone));
+		set_page_zone(page, zone_idx(zone));
+		prep_compound_tail(page, NULL, order);
 	}
 
 	page = virt_to_page(addr);
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-sparse-relax-struct-mem_section-size-constraints.patch
mm-sparse-vmemmap-rename-hvo-order-macros.patch
mm-mm_init-skip-initializing-shared-vmemmap-tail-pages.patch
mm-sparse-vmemmap-initialize-shared-tail-vmemmap-pages-on-allocation.patch
mm-sparse-vmemmap-support-section-based-vmemmap-accounting.patch
mm-mm_init-factor-out-pfn_to_zone.patch
mm-sparse-vmemmap-move-helpers-ahead-of-future-callers.patch
mm-sparse-vmemmap-support-section-based-vmemmap-optimization.patch
mm-sparse-initialize-memory-sections-earlier.patch
mm-hugetlb-switch-hugetlb-to-section-based-vmemmap-optimization.patch
mm-sparse-vmemmap-remove-sparsemem_vmemmap_preinit-support.patch
mm-sparse-inline-usemap-allocation-into-sparse_init_nid.patch
mm-sparse-remove-section_map_size.patch
mm-hugetlb-remove-huge_bootmem_hvo.patch
mm-hugetlb-remove-huge_bootmem_cma.patch
mm-hugetlb-localize-struct-huge_bootmem_page.patch
mm-hugetlb-localize-huge_bootmem_zones_valid.patch
mm-sparse-vmemmap-introduce-config_sparsemem_vmemmap_optimization.patch
mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.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-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