On Thu, Aug 28, 2025 at 12:01:17AM +0200, David Hildenbrand wrote:
We can now safely iterate over all pages in a folio, so no need for the pfn_to_page().
Also, as we already force the refcount in __init_single_page() to 1, we can just set the refcount to 0 and avoid page_ref_freeze() + VM_BUG_ON. Likely, in the future, we would just want to tell __init_single_page() to which value to initialize the refcount.
Further, adjust the comments to highlight that we are dealing with an open-coded prep_compound_page() variant, and add another comment explaining why we really need the __init_single_page() only on the tail pages.
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 | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 4a97e4f14c0dc..1f42186a85ea4 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3237,17 +3237,18 @@ static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio, { enum zone_type zone = zone_idx(folio_zone(folio)); int nid = folio_nid(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;
- int ret;
- for (pfn = head_pfn + start_page_number; pfn < end_pfn; pfn++) {
struct page *page = pfn_to_page(pfn);
- /*
* We mark all tail pages with memblock_reserved_mark_noinit(),* so these pages are completely uninitialized.
^ not? ;-)
*/- 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);
ret = page_ref_freeze(page, 1);VM_BUG_ON(!ret);
set_page_count(page, 0);} @@ -3257,12 +3258,15 @@ 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 initializing/preparing+freezing them in the* same go.*/
- /* 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