On 12/1/25 9:46 AM, 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 swap
> PTEs
>
> - 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 shared
> PTEs
>
> 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 dont 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.
>
> Reviewed-by: Baolin Wang <[email protected]>
> Signed-off-by: Nico Pache <[email protected]>
> ---
> Documentation/admin-guide/mm/transhuge.rst | 24 ++++++++++++++++++++++
> include/linux/huge_mm.h | 3 +++
> mm/huge_memory.c | 7 +++++++
> mm/khugepaged.c | 16 ++++++++++++---
> 4 files changed, 47 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst
> b/Documentation/admin-guide/mm/transhuge.rst
> index c51932e6275d..d396d1bfb274 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -714,6 +714,30 @@ nr_anon_partially_mapped
> an anonymous THP as "partially mapped" and count it here, even though
> it
> is not actually partially mapped anymore.
>
> +collapse_exceed_none_pte
> + The number of collapse attempts that failed due to exceeding the
> + max_ptes_none threshold. For mTHP collapse, Currently only
> max_ptes_none
currently
> + values of 0 and (HPAGE_PMD_NR - 1) are supported. Any other value will
> + emit a warning and no mTHP collapse will be attempted. khugepaged will
> + try to collapse to the largest enabled (m)THP size, if it fails, it
> will
size. If
or
size; if
> + try the next lower enabled mTHP size. This counter records the number
> of
> + times a collapse attempt was skipped for exceeding the max_ptes_none
> + threshold, and khugepaged will move on to the next available mTHP
> size.
> +
> +collapse_exceed_swap_pte
> + The number of anonymous mTHP pte ranges which were unable to collapse
> due
PTE
> + to containing at least one swap PTE. Currently khugepaged does not
> + support collapsing mTHP regions that contain a swap PTE. This counter
> can
> + be used to monitor the number of khugepaged mTHP collapses that failed
> + due to the presence of a swap PTE.
> +
> +collapse_exceed_shared_pte
> + The number of anonymous mTHP pte ranges which were unable to collapse
> due
PTE
> + to containing at least one shared PTE. Currently khugepaged does not
> + support collapsing mTHP pte ranges that contain a shared PTE. This
PTE
> + counter can be used to monitor the number of khugepaged mTHP collapses
> + that failed due to the presence of a shared PTE.
> +
> As the system ages, allocating huge pages may be expensive as the
> system uses memory compaction to copy data around memory to free a
> huge page for use. There are some counters in ``/proc/vmstat`` to help
--
~Randy
