On 1 Dec 2025, at 12:46, Nico Pache wrote:

The khugepaged daemon and madvise_collapse have two different
implementations that do almost the same thing.

Create collapse_single_pmd to increase code reuse and create an entry
point to these two users.

Refactor madvise_collapse and collapse_scan_mm_slot to use the new
collapse_single_pmd function. This introduces a minor behavioral change
that is most likely an undiscovered bug. The current implementation of
khugepaged tests collapse_test_exit_or_disable before calling
collapse_pte_mapped_thp, but we weren't doing it in the madvise_collapse
case. By unifying these two callers madvise_collapse now also performs
this check. We also modify the return value to be SCAN_ANY_PROCESS which
properly indicates that this process is no longer valid to operate on.

We also guard the khugepaged_pages_collapsed variable to ensure its only
incremented for khugepaged.

Reviewed-by: Wei Yang <redacted>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lorenzo Stoakes <redacted>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <redacted>
Signed-off-by: Nico Pache <npache@redhat.com>
---
 mm/khugepaged.c | 97 ++++++++++++++++++++++++++-----------------------
 1 file changed, 52 insertions(+), 45 deletions(-)

LGTM. Reviewed-by: Zi Yan [off-list ref]

Best Regards,
Yan, Zi