[to-be-updated] mm-sparse-relax-struct-mem_section-size-constraints.patch removed from -mm tree

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

The quilt patch titled
     Subject: mm/sparse: relax struct mem_section size constraints
has been removed from the -mm tree.  Its filename was
     mm-sparse-relax-struct-mem_section-size-constraints.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm/sparse: relax struct mem_section size constraints
Date: Tue, 25 Aug 2026 16:45:52 +0800

Patch series "mm: Introduce section-based vmemmap optimization for
HugeTLB", v5.

HugeTLB vmemmap optimization currently has its own early boot setup
path. It pre-populates optimized vmemmap mappings before the normal
sparse-vmemmap population code runs, and sparsemem carries
SPARSEMEM_VMEMMAP_PREINIT only to support that special case.

That makes the HugeTLB vmemmap optimization path harder to share with
other users of sparse-vmemmap optimization and leaves a fair amount of
HugeTLB-specific boot-time state in the generic memory initialization
flow.

This series introduces section-based vmemmap optimization support in
the sparse-vmemmap code and switches HugeTLB bootmem pages over to it.
Instead of having HugeTLB pre-populate optimized vmemmap mappings
itself, HugeTLB now records the compound page order in the corresponding
memory sections. The generic sparse-vmemmap population path can then
allocate or reuse shared tail vmemmap pages based on section metadata.

The patches are organized as follows:

  - patches 1-2 prepare sparsemem and vmemmap optimization metadata
  - patches 3-8 teach the common sparse-vmemmap paths to use that state
  - patches 9-10 switch HugeTLB bootmem optimization to the
    section-based path
  - patches 11-17 clean up sparsemem and HugeTLB bootmem code that is no
    longer needed after the conversion

This is intended to be the second smaller step toward the broader HVO
generalization [1].  The device DAX conversion and the wider HVO
consolidation are left for follow-up series.


This patch (of 17):

struct mem_section is currently forced to a power-of-2 size so the
section-to-root lookup can use a mask instead of a modulo.

That requirement makes future extensions harder than necessary: adding a
small field can require configuration-dependent padding or layout checks
just to preserve the lookup scheme.  Keep the lookup correct for any
struct mem_section size by using a plain modulo instead.

Do not leave the layout entirely unconstrained, though.  Keep struct
mem_section double-word aligned so modest size changes, such as adding
another word-sized field on 64-bit systems, still keep a compact and
efficient layout.  If future fields grow the structure beyond that sweet
spot, the lookup remains correct; only the exact layout efficiency
changes.

Link: https://lore.kernel.org/20260825084608.47437-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/20260825084608.47437-2-songmuchun@bytedance.com
Link: https://lore.kernel.org/linux-mm/20260513130542.35604-1-songmuchun@bytedance.com/ [1]
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: David Laight <david.laight.linux@gmail.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Qi Zheng <qi.zheng@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mmzone.h  |   11 +++--------
 mm/sparse.c             |    2 --
 scripts/gdb/linux/mm.py |    6 ++----
 3 files changed, 5 insertions(+), 14 deletions(-)

--- a/include/linux/mmzone.h~mm-sparse-relax-struct-mem_section-size-constraints
+++ a/include/linux/mmzone.h
@@ -2027,13 +2027,9 @@ struct mem_section {
 	 * section. (see page_ext.h about this.)
 	 */
 	struct page_ext *page_ext;
-	unsigned long pad;
 #endif
-	/*
-	 * WARNING: mem_section must be a power-of-2 in size for the
-	 * calculation and use of SECTION_ROOT_MASK to make sense.
-	 */
-};
+/* Sacrifice minor padding space for efficient lookup. */
+} __aligned(2 * sizeof(unsigned long));
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
 #define SECTIONS_PER_ROOT       (PAGE_SIZE / sizeof (struct mem_section))
@@ -2043,7 +2039,6 @@ struct mem_section {
 
 #define SECTION_NR_TO_ROOT(sec)	((sec) / SECTIONS_PER_ROOT)
 #define NR_SECTION_ROOTS	DIV_ROUND_UP(NR_MEM_SECTIONS, SECTIONS_PER_ROOT)
-#define SECTION_ROOT_MASK	(SECTIONS_PER_ROOT - 1)
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
 extern struct mem_section **mem_section;
@@ -2067,7 +2062,7 @@ static inline struct mem_section *__nr_t
 	if (!mem_section || !mem_section[root])
 		return NULL;
 #endif
-	return &mem_section[root][nr & SECTION_ROOT_MASK];
+	return &mem_section[root][nr % SECTIONS_PER_ROOT];
 }
 
 /*
--- a/mm/sparse.c~mm-sparse-relax-struct-mem_section-size-constraints
+++ a/mm/sparse.c
@@ -322,8 +322,6 @@ void __init sparse_init(void)
 	unsigned long pnum_end, pnum_begin, map_count = 1;
 	int nid_begin;
 
-	/* see include/linux/mmzone.h 'struct mem_section' definition */
-	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
 	memblocks_present();
 
 	if (compound_info_has_mask()) {
--- a/scripts/gdb/linux/mm.py~mm-sparse-relax-struct-mem_section-size-constraints
+++ a/scripts/gdb/linux/mm.py
@@ -70,7 +70,6 @@ class x86_page_ops():
             self.SECTIONS_PER_ROOT = 1
 
         self.NR_SECTION_ROOTS = DIV_ROUND_UP(self.NR_MEM_SECTIONS, self.SECTIONS_PER_ROOT)
-        self.SECTION_ROOT_MASK = self.SECTIONS_PER_ROOT - 1
 
         try:
             self.SECTION_HAS_MEM_MAP = 1 << int(gdb.parse_and_eval('SECTION_HAS_MEM_MAP_BIT'))
@@ -100,7 +99,7 @@ class x86_page_ops():
     def __nr_to_section(self, nr):
         root = self.SECTION_NR_TO_ROOT(nr)
         mem_section = gdb.parse_and_eval("mem_section")
-        return mem_section[root][nr & self.SECTION_ROOT_MASK]
+        return mem_section[root][nr % self.SECTIONS_PER_ROOT]
 
     def pfn_to_section_nr(self, pfn):
         return pfn >> self.PFN_SECTION_SHIFT
@@ -249,7 +248,6 @@ class aarch64_page_ops():
             self.SECTIONS_PER_ROOT = 1
 
         self.NR_SECTION_ROOTS = DIV_ROUND_UP(self.NR_MEM_SECTIONS, self.SECTIONS_PER_ROOT)
-        self.SECTION_ROOT_MASK = self.SECTIONS_PER_ROOT - 1
         self.SUBSECTION_SHIFT = 21
         self.SEBSECTION_SIZE = 1 << self.SUBSECTION_SHIFT
         self.PFN_SUBSECTION_SHIFT = self.SUBSECTION_SHIFT - self.PAGE_SHIFT
@@ -304,7 +302,7 @@ class aarch64_page_ops():
     def __nr_to_section(self, nr):
         root = self.SECTION_NR_TO_ROOT(nr)
         mem_section = gdb.parse_and_eval("mem_section")
-        return mem_section[root][nr & self.SECTION_ROOT_MASK]
+        return mem_section[root][nr % self.SECTIONS_PER_ROOT]
 
     def pfn_to_section_nr(self, pfn):
         return pfn >> self.PFN_SECTION_SHIFT
_

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

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-section-orders.patch
mm-sparse-vmemmap-set-section-order-for-device-dax.patch
mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch
mm-sparse-vmemmap-move-hvo-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