[PATCH RFC 10/35] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap()

David Hildenbrand
2025-08-21T20:07:44Z

All pages were already initialized and set to PageReserved() with a
refcount of 1 by MM init code.

In fact, by using __init_single_page(), we will be setting the refcount to
1 just to freeze it again immediately afterwards.

So drop the __init_single_page() and use __ClearPageReserved() instead.
Adjust the comments to highlight that we are dealing with an open-coded
prep_compound_page() variant.

Further, as we can now safely iterate over all pages in a folio, let's
avoid the page-pfn dance and just iterate the pages directly.

Note that the current code was likely problematic, but we never ran into
it: prep_compound_tail() would have been called with an offset that might
exceed a memory section, and prep_compound_tail() would have simply
added that offset to the page pointer -- which would not have done the
right thing on sparsemem without vmemmap.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/hugetlb.c | 21 ++++++++++-----------
1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d12a9d5146af4..ae82a845b14ad 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3235,17 +3235,14 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio,
unsigned long start_page_number,
unsigned long end_page_number)
{
- enum zone_type zone = zone_idx(folio_zone(folio));
- int nid = folio_nid(folio);
- unsigned long head_pfn = folio_pfn(folio);
- unsigned long pfn, end_pfn = head_pfn + end_page_number;
+ struct page *head_page = folio_page(folio, 0);
+ struct page *page = folio_page(folio, start_page_number);
+ unsigned long i;
int ret;

- for (pfn = head_pfn + start_page_number; pfn < end_pfn; pfn++) {
- struct page *page = pfn_to_page(pfn);
-
- __init_single_page(page, pfn, zone, nid);
- prep_compound_tail((struct page *)folio, pfn - head_pfn);
+ for (i = start_page_number; i < end_page_number; i++, page++) {
+ __ClearPageReserved(page);
+ prep_compound_tail(head_page, i);
ret = page_ref_freeze(page, 1);
VM_BUG_ON(!ret);
}
@@ -3257,12 +3254,14 @@ static void __init hugetlb_folio_init_vmemmap(struct folio *folio,
{
int ret;

- /* Prepare folio head */
+ /*
+ * This is an open-coded prep_compound_page() whereby we avoid
+ * walking pages twice by preparing+freezing them in the same go.
+ */
__folio_clear_reserved(folio);
__folio_set_head(folio);
ret = folio_ref_freeze(folio, 1);
VM_BUG_ON(!ret);
- /* Initialize the necessary tail struct pages */
hugetlb_folio_init_tail_vmemmap(folio, 1, nr_pages);
prep_compound_head((struct page *)folio, huge_page_order(h));
}
--
2.50.1