Re: [PATCH v2] khugepaged: remove redundant index check for pmd-folios

[Baolin Wang]

On 2/27/26 10:35 PM, Dev Jain wrote:
> Claim: folio_order(folio) == HPAGE_PMD_ORDER => folio->index == start.
>
> Proof: Both loops in hpage_collapse_scan_file and collapse_file, which
> iterate on the xarray, have the invariant that
> start <= folio->index < start + HPAGE_PMD_NR ... (i)
>
> A folio is always naturally aligned in the pagecache, therefore
> folio_order == HPAGE_PMD_ORDER => IS_ALIGNED(folio->index, HPAGE_PMD_NR) == true ... (ii)
>
> thp_vma_allowable_order -> thp_vma_suitable_order requires that the virtual
> offsets in the VMA are aligned to the order,
> => IS_ALIGNED(start, HPAGE_PMD_NR) == true ... (iii)
>
> Combining (i), (ii) and (iii), the claim is proven.
>
> Therefore, remove this check.
> While at it, simplify the comments.
>
> Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
> ---

Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>