diff options
| author | Lance Yang <lance.yang@linux.dev> | 2026-06-09 20:04:43 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-06-21 11:37:13 -0700 |
| commit | c85418be96666be9d6127448baad95ca404ee34e (patch) | |
| tree | 7f31265710c72f3fa71d9da30724f181dd1f90f2 /mm | |
| parent | cae43f22de82130a8fc1afa7b9b26fa8c08665f5 (diff) | |
| download | ath-c85418be96666be9d6127448baad95ca404ee34e.tar.gz | |
mm/khugepaged: fix PMD collapse swap PTE accounting
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.
Link: https://lore.kernel.org/20260609120443.71864-1-lance.yang@linux.dev
Fixes: 90ed32d00054 ("mm/khugepaged: introduce mTHP collapse support")
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: Nico Pache <npache@redhat.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/khugepaged.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 6de1a148222a0..33ab5d12e1bc7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1502,6 +1502,14 @@ static enum scan_result mthp_collapse(struct mm_struct *mm, nr_occupied_ptes = bitmap_weight_from(cc->mthp_present_ptes, offset, offset + nr_ptes); + /* + * Swap PTEs accepted during the scan are counted in @unmapped, + * not in the present-PTE bitmap. Account them for the PMD-order + * candidate. + */ + if (is_pmd_order(order)) + nr_occupied_ptes += unmapped; + if (nr_occupied_ptes >= nr_ptes - max_ptes_none) { enum scan_result ret; |