Re: [PATCH mm-unstable v19 08/14] mm/khugepaged: add per-order mTHP collapse failure statistics

[Lance Yang <lance.yang@linux.dev>]

On Fri, Jun 05, 2026 at 10:14:15AM -0600, Nico Pache wrote:
>Add three new mTHP statistics to track collapse failures for different
>orders when encountering swap PTEs, excessive none PTEs, and shared PTEs:
>
>- collapse_exceed_swap_pte: Increment when mTHP collapse fails due to
>	encountering a swap PTE.
>
>- collapse_exceed_none_pte: Counts when mTHP collapse fails due to
>  	exceeding the none PTE threshold for the given order
>
>- collapse_exceed_shared_pte: Counts when mTHP collapse fails due to
>	encountering a shared PTE.
>
>These statistics complement the existing THP_SCAN_EXCEED_* events by
>providing per-order granularity for mTHP collapse attempts. The stats are
>exposed via sysfs under
>`/sys/kernel/mm/transparent_hugepage/hugepages-*/stats/` for each
>supported hugepage size.
>
>As we currently do not support collapsing mTHPs that contain a swap or
>shared entry, those statistics keep track of how often we are
>encountering failed mTHP collapses due to these restrictions.
>
>We will add support for mTHP collapse for anonymous pages next; lets also
>track when this happens at the PMD level within the per-mTHP stats.
>
>Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
>Acked-by: David Hildenbrand (Arm) <david@kernel.org>
>Signed-off-by: Nico Pache <npache@redhat.com>
>---

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