Re: [PATCHv7 08/18] mm/sparse: Check memmap alignment for compound_info_has_mask()

David Hildenbrand (Arm)
2026-03-16T16:33:57Z

On 2/27/26 20:42, Kiryl Shutsemau (Meta) wrote:
> From: Kiryl Shutsemau <kas@kernel.org>
>
> If page->compound_info encodes a mask, it is expected that vmemmap to be
> naturally aligned to the maximum folio size.
>
> Add a VM_WARN_ON_ONCE() to check the alignment.
>
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Acked-by: Zi Yan <ziy@nvidia.com>
> ---
> mm/sparse.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index b5b2b6f7041b..dfabe554adf8 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -600,6 +600,11 @@ void __init sparse_init(void)
> BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
> memblocks_present();
>
> + if (compound_info_has_mask()) {
> + VM_WARN_ON_ONCE(!IS_ALIGNED((unsigned long) pfn_to_page(0),
> + MAX_FOLIO_VMEMMAP_ALIGN));
> + }

You could drop the {} or incorporate it into the VM_WARN_ON_ONCE

VM_WARN_ON_ONCE(compound_info_has_mask() &&
!IS_ALIGNED((unsigned long) pfn_to_page(0),
MAX_FOLIO_VMEMMAP_ALIGN)

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

--
Cheers,

David