linux-kernel - [PATCH 01/11] mm: Change the interface of prep_compound

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Message-ID: <20251205194351.1646318-2-kas@kernel.org>
Date: Fri,  5 Dec 2025 19:43:37 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>
Cc: David Hildenbrand <david@...nel.org>,
	Oscar Salvador <osalvador@...e.de>,
	Mike Rapoport <rppt@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Matthew Wilcox <willy@...radead.org>,
	Zi Yan <ziy@...dia.com>,
	Baoquan He <bhe@...hat.com>,
	Michal Hocko <mhocko@...e.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Jonathan Corbet <corbet@....net>,
	Usama Arif <usamaarif642@...il.com>,
	kernel-team@...a.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Kiryl Shutsemau <kas@...nel.org>
Subject: [PATCH 01/11] mm: Change the interface of prep_compound_tail()

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@...nel.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