+ x86-mm-stop-marking-vmemmap-as-section_info.patch added to mm-new branch

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

The patch titled
     Subject: x86/mm: stop marking vmemmap as SECTION_INFO
has been added to the -mm mm-new branch.  Its filename is
     x86-mm-stop-marking-vmemmap-as-section_info.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-mm-stop-marking-vmemmap-as-section_info.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: "David Hildenbrand (Arm)" <david@kernel.org>
Subject: x86/mm: stop marking vmemmap as SECTION_INFO
Date: Wed, 08 Jul 2026 16:11:00 +0200

We added the whole bootmem registration machinery in commit 04753278769f
("memory hotplug: register section/node id to free").

The main use case was to remember to which memory section memmap pages
belonged, so the memmap could be handled accordingly when freeing memory.

However, all that machinery is not required anymore: a memory section can
only get offlined if *all* pages can get offlined; and it can only get
unplugged once offline.  If some of these pages are unmovable memmap
pages: bad luck, doesn't work.  Offlining will fail.

Further, a lot of this machinery was required for pre-vmemmap support.
Now we only support the vmemmap with memory hotplug.

So the whole machinery is useless today.  Let's start by removing the last
pieces by first stopping to mark vmemmap pages as SECTION_INFO.  In
free_vmemmap_pages(), we can now always just free the reserved pages
directly.

Link: https://lore.kernel.org/20260708-bootmem_info_part2-v1-5-156ce4986598@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/mm/init_64.c |   30 ++++--------------------------
 1 file changed, 4 insertions(+), 26 deletions(-)

--- a/arch/x86/mm/init_64.c~x86-mm-stop-marking-vmemmap-as-section_info
+++ a/arch/x86/mm/init_64.c
@@ -1024,19 +1024,12 @@ static void __meminit free_vmemmap_pages
 {
 	unsigned long nr_pages = 1u << order;
 
-	if (altmap) {
+	if (altmap)
 		vmem_altmap_free(altmap, nr_pages);
-	} else if (PageReserved(page)) {
-		if (IS_ENABLED(CONFIG_HAVE_BOOTMEM_INFO_NODE) &&
-		    bootmem_type(page) == SECTION_INFO) {
-			while (nr_pages--)
-				put_page_bootmem(page++);
-		} else {
-			free_reserved_pages(page, order);
-		}
-	} else {
+	else if (PageReserved(page))
+		free_reserved_pages(page, order);
+	else
 		__free_pages(page, order);
-	}
 }
 
 static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
@@ -1593,12 +1586,8 @@ void register_page_bootmem_memmap(unsign
 	p4d_t *p4d;
 	pud_t *pud;
 	pmd_t *pmd;
-	unsigned int nr_pmd_pages;
-	struct page *page;
 
 	for (; addr < end; addr = next) {
-		pte_t *pte = NULL;
-
 		pgd = pgd_offset_k(addr);
 		if (pgd_none(*pgd)) {
 			next = (addr + PAGE_SIZE) & PAGE_MASK;
@@ -1630,19 +1619,8 @@ void register_page_bootmem_memmap(unsign
 			next = (addr + PAGE_SIZE) & PAGE_MASK;
 			get_page_bootmem(section_nr, pmd_page(*pmd),
 					 MIX_SECTION_INFO);
-
-			pte = pte_offset_kernel(pmd, addr);
-			if (pte_none(*pte))
-				continue;
-			get_page_bootmem(section_nr, pte_page(*pte),
-					 SECTION_INFO);
 		} else {
 			next = pmd_addr_end(addr, end);
-			nr_pmd_pages = (next - addr) >> PAGE_SHIFT;
-			page = pmd_page(*pmd);
-			while (nr_pmd_pages--)
-				get_page_bootmem(section_nr, page++,
-						 SECTION_INFO);
 		}
 	}
 }
_

Patches currently in -mm which might be from david@kernel.org are

sparc-mm-drop-custom-pte_clear_not_present_full.patch
mm-drop-pte_clear_not_present_full.patch
mm-cleanup-clear_not_present_full_ptes-and-rename-to-clear_non_present_ptes.patch
x86-mm-drop-order-parameter-from-free_pagetable.patch
mm-provide-free_reserved_pages-removing-x86-variant.patch
s390-mm-use-free_reserved_pages-in-vmem_free_pages.patch
mm-bootmem_info-allow-calling-free_bootmem_page-on-pages-without-a-bootmem_type.patch
x86-mm-stop-marking-vmemmap-as-section_info.patch
x86-mm-stop-marking-page-tables-as-mix_section_info.patch
x86-mm-remove-config_have_bootmem_info_node.patch
mm-hugetlb_vmemmap-remove-bootmem_info-leftovers.patch
mm-sparse-remove-bootmem_infoh-include.patch
mm-bootmem_info-remove-config_have_bootmem_info_node.patch