[PATCH v10 12/13] khugepaged: add per-order mTHP khugepaged stats

Nico Pache
2025-08-19T14:17:02Z

With mTHP support inplace, let add the per-order mTHP stats for
exceeding NONE, SWAP, and SHARED.

Signed-off-by: Nico Pache <npache@redhat.com>
---
Documentation/admin-guide/mm/transhuge.rst | 17 +++++++++++++++++
include/linux/huge_mm.h | 3 +++
mm/huge_memory.c | 7 +++++++
mm/khugepaged.c | 16 +++++++++++++---
4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 7ccb93e22852..b85547ac4fe9 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -705,6 +705,23 @@ 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_swap_pte
+ The number of anonymous THP which contain at least one swap PTE.
+ Currently khugepaged does not support collapsing mTHP regions that
+ contain a swap PTE.
+
+collapse_exceed_none_pte
+ The number of anonymous THP which have exceeded the none PTE threshold.
+ With mTHP collapse, a bitmap is used to gather the state of a PMD region
+ and is then recursively checked from largest to smallest order against
+ the scaled max_ptes_none count. This counter indicates that the next
+ enabled order will be checked.
+
+collapse_exceed_shared_pte
+ The number of anonymous THP which contain at least one shared PTE.
+ Currently khugepaged does not support collapsing mTHP regions that
+ contain 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
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 4ada5d1f7297..6f1593d0b4b5 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -144,6 +144,9 @@ enum mthp_stat_item {
MTHP_STAT_SPLIT_DEFERRED,
MTHP_STAT_NR_ANON,
MTHP_STAT_NR_ANON_PARTIALLY_MAPPED,
+ MTHP_STAT_COLLAPSE_EXCEED_SWAP,
+ MTHP_STAT_COLLAPSE_EXCEED_NONE,
+ MTHP_STAT_COLLAPSE_EXCEED_SHARED,
__MTHP_STAT_COUNT
};

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 20d005c2c61f..9f0470c3e983 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -639,6 +639,10 @@ DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
DEFINE_MTHP_STAT_ATTR(nr_anon, MTHP_STAT_NR_ANON);
DEFINE_MTHP_STAT_ATTR(nr_anon_partially_mapped, MTHP_STAT_NR_ANON_PARTIALLY_MAPPED);
+DEFINE_MTHP_STAT_ATTR(collapse_exceed_swap_pte, MTHP_STAT_COLLAPSE_EXCEED_SWAP);
+DEFINE_MTHP_STAT_ATTR(collapse_exceed_none_pte, MTHP_STAT_COLLAPSE_EXCEED_NONE);
+DEFINE_MTHP_STAT_ATTR(collapse_exceed_shared_pte, MTHP_STAT_COLLAPSE_EXCEED_SHARED);
+

static struct attribute *anon_stats_attrs[] = {
&anon_fault_alloc_attr.attr,
@@ -655,6 +659,9 @@ static struct attribute *anon_stats_attrs[] = {
&split_deferred_attr.attr,
&nr_anon_attr.attr,
&nr_anon_partially_mapped_attr.attr,
+ &collapse_exceed_swap_pte_attr.attr,
+ &collapse_exceed_none_pte_attr.attr,
+ &collapse_exceed_shared_pte_attr.attr,
NULL,
};

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index c13bc583a368..5a3386043f39 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -594,7 +594,9 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
continue;
} else {
result = SCAN_EXCEED_NONE_PTE;
- count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+ if (order == HPAGE_PMD_ORDER)
+ count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_NONE);
goto out;
}
}
@@ -633,10 +635,17 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
* shared may cause a future higher order collapse on a
* rescan of the same range.
*/
- if (order != HPAGE_PMD_ORDER || (cc->is_khugepaged &&
- shared > khugepaged_max_ptes_shared)) {
+ if (order != HPAGE_PMD_ORDER) {
+ result = SCAN_EXCEED_SHARED_PTE;
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED);
+ goto out;
+ }
+
+ if (cc->is_khugepaged &&
+ shared > khugepaged_max_ptes_shared) {
result = SCAN_EXCEED_SHARED_PTE;
count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED);
goto out;
}
}
@@ -1084,6 +1093,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
* range.
*/
if (order != HPAGE_PMD_ORDER) {
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SWAP);
pte_unmap(pte);
mmap_read_unlock(mm);
result = SCAN_EXCEED_SWAP_PTE;
--
2.50.1