Re: [PATCHv6 09/17] mm/sparse: Check memmap alignment for compound_info_has_mask()

David Hildenbrand (Arm)
2026-02-05T13:31:31Z

On 2/2/26 16:56, Kiryl Shutsemau wrote:
> If page->compound_info encodes a mask, it is expected that vmemmap to be
> naturally aligned to the maximum folio size.
>
> Add a VM_BUG_ON() to check the alignment.
>
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Acked-by: Zi Yan <ziy@nvidia.com>
> ---
> mm/sparse.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index b5b2b6f7041b..6c9b62607f3f 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -600,6 +600,13 @@ void __init sparse_init(void)
> BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
> memblocks_present();
>
> + if (compound_info_has_mask()) {
> + unsigned long alignment;
> +
> + alignment = MAX_FOLIO_NR_PAGES * sizeof(struct page);
> + VM_BUG_ON(!IS_ALIGNED((unsigned long) pfn_to_page(0), alignment));

No VM_BUG_ON. VM_WARN_ON_ONCE() should be good enough, no?

As discussed in the other thread, is checking for MAX_FOLIO_NR_PAGES
alignment sufficient?

--
Cheers,

David