Re: [PATCH mm-unstable 1/1] mm/khugepaged: fix PMD collapse swap PTE accounting

[David Hildenbrand (Arm)]

On 6/9/26 14:04, Lance Yang wrote:
> From: Lance Yang <lance.yang@xxxxxxxxx>
> 
> mthp_collapse() uses mthp_present_ptes to decide whether a range has
> enough occupied PTEs to try collapse. Swap PTEs accepted by
> collapse_scan_pmd() are counted in unmapped, but are not represented in
> mthp_present_ptes.
> 
> When lower orders are enabled, collapse_scan_pmd() relaxes max_ptes_none
> so the scan can cover the whole PMD and build the bitmap. mthp_collapse()
> then checks the PMD-order candidate using the bitmap.
> 
> With max_ptes_none set to 0, a range with 511 present PTEs and one swap
> PTE no longer reaches collapse_huge_page(), even though PMD collapse can
> handle swap PTEs up to max_ptes_swap.
> 
> Account unmapped PTEs only for PMD order. PMD collapse supports swap PTEs
> through max_ptes_swap, while lower-order mTHP collapse does not currently
> support non-present PTEs. Keep non-present PTEs out of the lower-order
> eligibility check.
> 
> Signed-off-by: Lance Yang <lance.yang@xxxxxxxxx>
> ---
> Sent separately, as discussed in [1], to spell out the PMD-order swap PTE
> case. Patch [2] is still only in mm-unstable, so no Fixes: tag.

Right, probably we just want to add the Fixes: tag once Andrew moves the series
to mm-stable?

-- 
Cheers,

David