* + mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info.patch added to mm-new branch
@ 2026-02-27 20:09 Andrew Morton
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From: Andrew Morton @ 2026-02-27 20:09 UTC (permalink / raw)
To: mm-commits, ziy, willy, vbabka, usamaarif642, rppt,
roman.gushchin, rientjes, paul.walmsley, palmer, osalvador,
muchun.song, mhocko, lorenzo.stoakes, kernel, harry.yoo, hannes,
fvdl, david, corbet, cl, chenhuacai, bhe, aou, alex, kas, akpm
The patch titled
Subject: mm: rename the 'compound_head' field in the 'struct page' to 'compound_info'
has been added to the -mm mm-new branch. Its filename is
mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rename-the-compound_head-field-in-the-struct-page-to-compound_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.
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------------------------------------------------------
From: Kiryl Shutsemau <kas@kernel.org>
Subject: mm: rename the 'compound_head' field in the 'struct page' to 'compound_info'
Date: Fri, 27 Feb 2026 19:42:41 +0000
The 'compound_head' field in the 'struct page' encodes whether the page is
a tail and where to locate the head page. Bit 0 is set if the page is a
tail, and the remaining bits in the field point to the head page.
As preparation for changing how the field encodes information about the
head page, rename the field to 'compound_info'.
Link: https://lkml.kernel.org/r/20260227194302.274384-4-kas@kernel.org
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (arm) <david@kernel.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: WANG Xuerui <kernel@xen0n.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
Documentation/admin-guide/kdump/vmcoreinfo.rst | 2 -
Documentation/mm/vmemmap_dedup.rst | 6 ++--
include/linux/mm_types.h | 20 +++++++--------
include/linux/page-flags.h | 18 ++++++-------
include/linux/types.h | 2 -
kernel/vmcore_info.c | 2 -
mm/page_alloc.c | 2 -
mm/slab.h | 2 -
mm/util.c | 2 -
9 files changed, 28 insertions(+), 28 deletions(-)
--- a/Documentation/admin-guide/kdump/vmcoreinfo.rst~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/Documentation/admin-guide/kdump/vmcoreinfo.rst
@@ -141,7 +141,7 @@ nodemask_t
The size of a nodemask_t type. Used to compute the number of online
nodes.
-(page, flags|_refcount|mapping|lru|_mapcount|private|compound_order|compound_head)
+(page, flags|_refcount|mapping|lru|_mapcount|private|compound_order|compound_info)
----------------------------------------------------------------------------------
User-space tools compute their values based on the offset of these
--- a/Documentation/mm/vmemmap_dedup.rst~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/Documentation/mm/vmemmap_dedup.rst
@@ -24,7 +24,7 @@ For each base page, there is a correspon
Within the HugeTLB subsystem, only the first 4 ``struct page`` are used to
contain unique information about a HugeTLB page. ``__NR_USED_SUBPAGE`` provides
this upper limit. The only 'useful' information in the remaining ``struct page``
-is the compound_head field, and this field is the same for all tail pages.
+is the compound_info field, and this field is the same for all tail pages.
By removing redundant ``struct page`` for HugeTLB pages, memory can be returned
to the buddy allocator for other uses.
@@ -124,10 +124,10 @@ Here is how things look before optimizat
| |
+-----------+
-The value of page->compound_head is the same for all tail pages. The first
+The value of page->compound_info is the same for all tail pages. The first
page of ``struct page`` (page 0) associated with the HugeTLB page contains the 4
``struct page`` necessary to describe the HugeTLB. The only use of the remaining
-pages of ``struct page`` (page 1 to page 7) is to point to page->compound_head.
+pages of ``struct page`` (page 1 to page 7) is to point to page->compound_info.
Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of ``struct page``
will be used for each HugeTLB page. This will allow us to free the remaining
7 pages to the buddy allocator.
--- a/include/linux/mm_types.h~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/include/linux/mm_types.h
@@ -126,14 +126,14 @@ struct page {
atomic_long_t pp_ref_count;
};
struct { /* Tail pages of compound page */
- unsigned long compound_head; /* Bit zero is set */
+ unsigned long compound_info; /* Bit zero is set */
};
struct { /* ZONE_DEVICE pages */
/*
- * The first word is used for compound_head or folio
+ * The first word is used for compound_info or folio
* pgmap
*/
- void *_unused_pgmap_compound_head;
+ void *_unused_pgmap_compound_info;
void *zone_device_data;
/*
* ZONE_DEVICE private pages are counted as being
@@ -409,7 +409,7 @@ struct folio {
/* private: avoid cluttering the output */
/* For the Unevictable "LRU list" slot */
struct {
- /* Avoid compound_head */
+ /* Avoid compound_info */
void *__filler;
/* public: */
unsigned int mlock_count;
@@ -510,7 +510,7 @@ struct folio {
FOLIO_MATCH(flags, flags);
FOLIO_MATCH(lru, lru);
FOLIO_MATCH(mapping, mapping);
-FOLIO_MATCH(compound_head, lru);
+FOLIO_MATCH(compound_info, lru);
FOLIO_MATCH(__folio_index, index);
FOLIO_MATCH(private, private);
FOLIO_MATCH(_mapcount, _mapcount);
@@ -529,7 +529,7 @@ FOLIO_MATCH(_last_cpupid, _last_cpupid);
static_assert(offsetof(struct folio, fl) == \
offsetof(struct page, pg) + sizeof(struct page))
FOLIO_MATCH(flags, _flags_1);
-FOLIO_MATCH(compound_head, _head_1);
+FOLIO_MATCH(compound_info, _head_1);
FOLIO_MATCH(_mapcount, _mapcount_1);
FOLIO_MATCH(_refcount, _refcount_1);
#undef FOLIO_MATCH
@@ -537,13 +537,13 @@ FOLIO_MATCH(_refcount, _refcount_1);
static_assert(offsetof(struct folio, fl) == \
offsetof(struct page, pg) + 2 * sizeof(struct page))
FOLIO_MATCH(flags, _flags_2);
-FOLIO_MATCH(compound_head, _head_2);
+FOLIO_MATCH(compound_info, _head_2);
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl) \
static_assert(offsetof(struct folio, fl) == \
offsetof(struct page, pg) + 3 * sizeof(struct page))
FOLIO_MATCH(flags, _flags_3);
-FOLIO_MATCH(compound_head, _head_3);
+FOLIO_MATCH(compound_info, _head_3);
#undef FOLIO_MATCH
/**
@@ -609,8 +609,8 @@ struct ptdesc {
#define TABLE_MATCH(pg, pt) \
static_assert(offsetof(struct page, pg) == offsetof(struct ptdesc, pt))
TABLE_MATCH(flags, pt_flags);
-TABLE_MATCH(compound_head, pt_list);
-TABLE_MATCH(compound_head, _pt_pad_1);
+TABLE_MATCH(compound_info, pt_list);
+TABLE_MATCH(compound_info, _pt_pad_1);
TABLE_MATCH(mapping, __page_mapping);
TABLE_MATCH(__folio_index, pt_index);
TABLE_MATCH(rcu_head, pt_rcu_head);
--- a/include/linux/page-flags.h~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/include/linux/page-flags.h
@@ -213,7 +213,7 @@ static __always_inline const struct page
/*
* Only addresses aligned with PAGE_SIZE of struct page may be fake head
* struct page. The alignment check aims to avoid access the fields (
- * e.g. compound_head) of the @page[1]. It can avoid touch a (possibly)
+ * e.g. compound_info) of the @page[1]. It can avoid touch a (possibly)
* cold cacheline in some cases.
*/
if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) &&
@@ -223,7 +223,7 @@ static __always_inline const struct page
* because the @page is a compound page composed with at least
* two contiguous pages.
*/
- unsigned long head = READ_ONCE(page[1].compound_head);
+ unsigned long head = READ_ONCE(page[1].compound_info);
if (likely(head & 1))
return (const struct page *)(head - 1);
@@ -281,7 +281,7 @@ static __always_inline int page_is_fake_
static __always_inline unsigned long _compound_head(const struct page *page)
{
- unsigned long head = READ_ONCE(page->compound_head);
+ unsigned long head = READ_ONCE(page->compound_info);
if (unlikely(head & 1))
return head - 1;
@@ -320,13 +320,13 @@ static __always_inline unsigned long _co
static __always_inline int PageTail(const struct page *page)
{
- return READ_ONCE(page->compound_head) & 1 || page_is_fake_head(page);
+ return READ_ONCE(page->compound_info) & 1 || page_is_fake_head(page);
}
static __always_inline int PageCompound(const struct page *page)
{
return test_bit(PG_head, &page->flags.f) ||
- READ_ONCE(page->compound_head) & 1;
+ READ_ONCE(page->compound_info) & 1;
}
#define PAGE_POISON_PATTERN -1l
@@ -348,7 +348,7 @@ static const unsigned long *const_folio_
{
const struct page *page = &folio->page;
- VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);
+ VM_BUG_ON_PGFLAGS(page->compound_info & 1, page);
VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);
return &page[n].flags.f;
}
@@ -357,7 +357,7 @@ static unsigned long *folio_flags(struct
{
struct page *page = &folio->page;
- VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);
+ VM_BUG_ON_PGFLAGS(page->compound_info & 1, page);
VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);
return &page[n].flags.f;
}
@@ -873,12 +873,12 @@ static inline bool folio_test_large(cons
static __always_inline void set_compound_head(struct page *tail,
const struct page *head, unsigned int order)
{
- WRITE_ONCE(tail->compound_head, (unsigned long)head + 1);
+ WRITE_ONCE(tail->compound_info, (unsigned long)head + 1);
}
static __always_inline void clear_compound_head(struct page *page)
{
- WRITE_ONCE(page->compound_head, 0);
+ WRITE_ONCE(page->compound_info, 0);
}
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
--- a/include/linux/types.h~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/include/linux/types.h
@@ -239,7 +239,7 @@ struct ustat {
*
* This guarantee is important for few reasons:
* - future call_rcu_lazy() will make use of lower bits in the pointer;
- * - the structure shares storage space in struct page with @compound_head,
+ * - the structure shares storage space in struct page with @compound_info,
* which encode PageTail() in bit 0. The guarantee is needed to avoid
* false-positive PageTail().
*/
--- a/kernel/vmcore_info.c~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/kernel/vmcore_info.c
@@ -198,7 +198,7 @@ static int __init crash_save_vmcoreinfo_
VMCOREINFO_OFFSET(page, lru);
VMCOREINFO_OFFSET(page, _mapcount);
VMCOREINFO_OFFSET(page, private);
- VMCOREINFO_OFFSET(page, compound_head);
+ VMCOREINFO_OFFSET(page, compound_info);
VMCOREINFO_OFFSET(pglist_data, node_zones);
VMCOREINFO_OFFSET(pglist_data, nr_zones);
#ifdef CONFIG_FLATMEM
--- a/mm/page_alloc.c~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/mm/page_alloc.c
@@ -732,7 +732,7 @@ static inline bool pcp_allowed_order(uns
* The first PAGE_SIZE page is called the "head page" and have PG_head set.
*
* The remaining PAGE_SIZE pages are called "tail pages". PageTail() is encoded
- * in bit 0 of page->compound_head. The rest of bits is pointer to head page.
+ * in bit 0 of page->compound_info. The rest of bits is pointer to head page.
*
* The first tail page's ->compound_order holds the order of allocation.
* This usage means that zero-order pages may not be compound.
--- a/mm/slab.h~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/mm/slab.h
@@ -94,7 +94,7 @@ struct slab {
#define SLAB_MATCH(pg, sl) \
static_assert(offsetof(struct page, pg) == offsetof(struct slab, sl))
SLAB_MATCH(flags, flags);
-SLAB_MATCH(compound_head, slab_cache); /* Ensure bit 0 is clear */
+SLAB_MATCH(compound_info, slab_cache); /* Ensure bit 0 is clear */
SLAB_MATCH(_refcount, __page_refcount);
#ifdef CONFIG_MEMCG
SLAB_MATCH(memcg_data, obj_exts);
--- a/mm/util.c~mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info
+++ a/mm/util.c
@@ -1276,7 +1276,7 @@ void snapshot_page(struct page_snapshot
again:
memset(&ps->folio_snapshot, 0, sizeof(struct folio));
memcpy(&ps->page_snapshot, page, sizeof(*page));
- head = ps->page_snapshot.compound_head;
+ head = ps->page_snapshot.compound_info;
if ((head & 1) == 0) {
ps->idx = 0;
foliop = (struct folio *)&ps->page_snapshot;
_
Patches currently in -mm which might be from kas@kernel.org are
mm-move-max_folio_order-definition-to-mmzoneh.patch
mm-change-the-interface-of-prep_compound_tail.patch
mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info.patch
mm-move-set-clear_compound_head-next-to-compound_head.patch
riscv-mm-align-vmemmap-to-maximal-folio-size.patch
loongarch-mm-align-vmemmap-to-maximal-folio-size.patch
mm-rework-compound_head-for-power-of-2-sizeofstruct-page.patch
mm-sparse-check-memmap-alignment-for-compound_info_has_mask.patch
mm-hugetlb-defer-vmemmap-population-for-bootmem-hugepages.patch
mm-hugetlb-refactor-code-around-vmemmap_walk.patch
x86-vdso-undefine-config_hugetlb_page_optimize_vmemmap-for-vdso32.patch
mm-hugetlb-remove-fake-head-pages.patch
mm-drop-fake-head-checks.patch
hugetlb-remove-vmemmap_synchronize_rcu.patch
mm-hugetlb-remove-hugetlb_optimize_vmemmap_key-static-key.patch
mm-remove-the-branch-from-compound_head.patch
hugetlb-update-vmemmap_deduprst.patch
mm-slab-use-compound_head-in-page_slab.patch
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2026-02-27 20:09 + mm-rename-the-compound_head-field-in-the-struct-page-to-compound_info.patch added to mm-new branch Andrew Morton
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