[PATCH 01/11] mm: Change the interface of prep_compound_tail()

Kiryl Shutsemau
2025-12-05T19:43:58Z

Instead of passing down the head page and tail page index, pass the tail
and head pages directly, as well as the order of the compound page.

This is a preparation for changing how the head position is encoded in
the tail page.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
---
include/linux/page-flags.h | 4 +++-
mm/hugetlb.c | 8 +++++---
mm/internal.h | 11 +++++------
mm/mm_init.c | 2 +-
mm/page_alloc.c | 2 +-
5 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 0091ad1986bf..2c1153dd7e0e 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -865,7 +865,9 @@ static inline bool folio_test_large(const struct folio *folio)
return folio_test_head(folio);
}

-static __always_inline void set_compound_head(struct page *page, struct page *head)
+static __always_inline void set_compound_head(struct page *page,
+ struct page *head,
+ unsigned int order)
{
WRITE_ONCE(page->compound_head, (unsigned long)head + 1);
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0455119716ec..a55d638975bd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3212,6 +3212,7 @@ int __alloc_bootmem_huge_page(struct hstate *h, int nid)

/* Initialize [start_page:end_page_number] tail struct pages of a hugepage */
static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio,
+ struct hstate *h,
unsigned long start_page_number,
unsigned long end_page_number)
{
@@ -3220,6 +3221,7 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio,
struct page *page = folio_page(folio, start_page_number);
unsigned long head_pfn = folio_pfn(folio);
unsigned long pfn, end_pfn = head_pfn + end_page_number;
+ unsigned int order = huge_page_order(h);

/*
* As we marked all tail pages with memblock_reserved_mark_noinit(),
@@ -3227,7 +3229,7 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio,
*/
for (pfn = head_pfn + start_page_number; pfn < end_pfn; page++, pfn++) {
__init_single_page(page, pfn, zone, nid);
- prep_compound_tail((struct page *)folio, pfn - head_pfn);
+ prep_compound_tail(page, &folio->page, order);
set_page_count(page, 0);
}
}
@@ -3247,7 +3249,7 @@ static void __init hugetlb_folio_init_vmemmap(struct folio *folio,
__folio_set_head(folio);
ret = folio_ref_freeze(folio, 1);
VM_BUG_ON(!ret);
- hugetlb_folio_init_tail_vmemmap(folio, 1, nr_pages);
+ hugetlb_folio_init_tail_vmemmap(folio, h, 1, nr_pages);
prep_compound_head((struct page *)folio, huge_page_order(h));
}

@@ -3304,7 +3306,7 @@ static void __init prep_and_add_bootmem_folios(struct hstate *h,
* time as this is early in boot and there should
* be no contention.
*/
- hugetlb_folio_init_tail_vmemmap(folio,
+ hugetlb_folio_init_tail_vmemmap(folio, h,
HUGETLB_VMEMMAP_RESERVE_PAGES,
pages_per_huge_page(h));
}
diff --git a/mm/internal.h b/mm/internal.h
index 1561fc2ff5b8..0355da7cb6df 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -810,13 +810,12 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
INIT_LIST_HEAD(&folio->_deferred_list);
}

-static inline void prep_compound_tail(struct page *head, int tail_idx)
+static inline void prep_compound_tail(struct page *tail,
+ struct page *head, unsigned int order)
{
- struct page *p = head + tail_idx;
-
- p->mapping = TAIL_MAPPING;
- set_compound_head(p, head);
- set_page_private(p, 0);
+ tail->mapping = TAIL_MAPPING;
+ set_compound_head(tail, head, order);
+ set_page_private(tail, 0);
}

void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags);
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 7712d887b696..87d1e0277318 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1102,7 +1102,7 @@ static void __ref memmap_init_compound(struct page *head,
struct page *page = pfn_to_page(pfn);

__init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
- prep_compound_tail(head, pfn - head_pfn);
+ prep_compound_tail(page, head, order);
set_page_count(page, 0);
}
prep_compound_head(head, order);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed82ee55e66a..fe77c00c99df 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -717,7 +717,7 @@ void prep_compound_page(struct page *page, unsigned int order)

__SetPageHead(page);
for (i = 1; i < nr_pages; i++)
- prep_compound_tail(page, i);
+ prep_compound_tail(page + i, page, order);

prep_compound_head(page, order);
}
--
2.51.2