Re: [PATCH] khugepaged: convert redundant check to WARN_ON

[Lance Yang]

On 2026/2/24 16:21, Baolin Wang wrote:
> On 2/19/26 1:48 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, convert this to a VM_WARN_ON.
> >
> > Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
> > ---
>
> Make sense to me. Personally, I’d like to keep this VM_WARN_ON() to 
> catch unexpected behavior.

+1

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>