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Message-ID: <20251201174627.23295-11-npache@redhat.com>
Date: Mon, 1 Dec 2025 10:46:21 -0700
From: Nico Pache <npache@...hat.com>
To: linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
linux-mm@...ck.org,
linux-doc@...r.kernel.org
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ziy@...dia.com,
baolin.wang@...ux.alibaba.com,
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Subject: [PATCH v13 mm-new 10/16] khugepaged: add per-order mTHP collapse failure statistics
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 <baolin.wang@...ux.alibaba.com>
Signed-off-by: Nico Pache <npache@...hat.com>
---
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
+ 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
+ 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
+ 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
+ to containing at least one shared PTE. Currently khugepaged does not
+ support collapsing mTHP pte ranges that contain a shared PTE. This
+ 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
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index f93365e182b4..1082b78e794d 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 c1e1e91b0e61..b4d9b3ac9a7c 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 b2ea56c9bb42..efb8a47af65a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -604,7 +604,9 @@ 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 (!is_mthp_order(order))
+ count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_NONE);
goto out;
}
}
@@ -634,10 +636,17 @@ 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 (is_mthp_order(order) || (cc->is_khugepaged &&
- shared > khugepaged_max_ptes_shared)) {
+ if (is_mthp_order(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;
}
}
@@ -1086,6 +1095,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
* range.
*/
if (is_mthp_order(order)) {
+ count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SWAP);
pte_unmap(pte);
mmap_read_unlock(mm);
result = SCAN_EXCEED_SWAP_PTE;
--
2.51.1
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