+ mm-khugepaged-introduce-a-count_collapse_event-helper.patch added to mm-unstable branch

The patch titled
     Subject: mm/khugepaged: introduce a count_collapse_event() helper
has been added to the -mm mm-unstable branch.  Its filename is
     mm-khugepaged-introduce-a-count_collapse_event-helper.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-introduce-a-count_collapse_event-helper.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Nico Pache (Red Hat)" <[email protected]>
Subject: mm/khugepaged: introduce a count_collapse_event() helper
Date: Tue, 11 Aug 2026 06:48:35 -0600

Provide a simple helper function to help reduce a often used, and
duplicate pattern across the khugepaged code.

When collapsing to a PMD we need to record a vm_event and the mTHP_stat
event.  When doing mTHP collapse we only update the mTHP stat.

Link: https://lore.kernel.org/[email protected]
Signed-off-by: Nico Pache (Red Hat) <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Acked-by: Usama Arif <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes (ARM) <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 mm/khugepaged.c |   42 +++++++++++++++++++++---------------------
 1 file changed, 21 insertions(+), 21 deletions(-)

--- a/mm/khugepaged.c~mm-khugepaged-introduce-a-count_collapse_event-helper
+++ a/mm/khugepaged.c
@@ -688,6 +688,14 @@ static inline bool folio_pte_referenced(
 	return pte_young(pteval) || mmu_notifier_test_young(vma->vm_mm, addr);
 }
 
+static void count_collapse_event(unsigned int order, enum vm_event_item vm_event,
+		enum mthp_stat_item mthp_event)
+{
+	if (is_pmd_order(order))
+		count_vm_event(vm_event);
+	count_mthp_stat(order, mthp_event);
+}
+
 static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		unsigned long start_addr, pte_t *pte, struct collapse_control *cc,
 		unsigned int order, struct list_head *compound_pagelist)
@@ -708,9 +716,8 @@ static enum scan_result __collapse_huge_
 		if (pte_none_or_zero(pteval)) {
 			if (++none_or_zero > max_ptes_none) {
 				result = SCAN_EXCEED_NONE_PTE;
-				if (is_pmd_order(order))
-					count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
-				count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_NONE);
+				count_collapse_event(order, THP_SCAN_EXCEED_NONE_PTE,
+						     MTHP_STAT_COLLAPSE_EXCEED_NONE);
 				goto out;
 			}
 			continue;
@@ -752,9 +759,8 @@ static enum scan_result __collapse_huge_
 			 */
 			if (++shared > max_ptes_shared) {
 				result = SCAN_EXCEED_SHARED_PTE;
-				if (is_pmd_order(order))
-					count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-				count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SHARED);
+				count_collapse_event(order, THP_SCAN_EXCEED_SHARED_PTE,
+						     MTHP_STAT_COLLAPSE_EXCEED_SHARED);
 				goto out;
 			}
 		}
@@ -1264,15 +1270,12 @@ static enum scan_result alloc_charge_fol
 	folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
 	if (!folio) {
 		*foliop = NULL;
-		if (is_pmd_order(order))
-			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
-		count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC_FAILED);
+		count_collapse_event(order, THP_COLLAPSE_ALLOC_FAILED,
+				     MTHP_STAT_COLLAPSE_ALLOC_FAILED);
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
 	}
 
-	if (is_pmd_order(order))
-		count_vm_event(THP_COLLAPSE_ALLOC);
-	count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC);
+	count_collapse_event(order, THP_COLLAPSE_ALLOC, MTHP_STAT_COLLAPSE_ALLOC);
 
 	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
 		folio_put(folio);
@@ -1662,9 +1665,8 @@ static enum scan_result collapse_scan_pm
 		if (pte_none_or_zero(pteval)) {
 			if (++none_or_zero > max_ptes_none) {
 				result = SCAN_EXCEED_NONE_PTE;
-				count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
-				count_mthp_stat(HPAGE_PMD_ORDER,
-						MTHP_STAT_COLLAPSE_EXCEED_NONE);
+				count_collapse_event(HPAGE_PMD_ORDER, THP_SCAN_EXCEED_NONE_PTE,
+						     MTHP_STAT_COLLAPSE_EXCEED_NONE);
 				goto out_unmap;
 			}
 			continue;
@@ -1672,9 +1674,8 @@ static enum scan_result collapse_scan_pm
 		if (!pte_present(pteval)) {
 			if (++unmapped > max_ptes_swap) {
 				result = SCAN_EXCEED_SWAP_PTE;
-				count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
-				count_mthp_stat(HPAGE_PMD_ORDER,
-						MTHP_STAT_COLLAPSE_EXCEED_SWAP);
+				count_collapse_event(HPAGE_PMD_ORDER, THP_SCAN_EXCEED_SWAP_PTE,
+						     MTHP_STAT_COLLAPSE_EXCEED_SWAP);
 				goto out_unmap;
 			}
 			/*
@@ -1731,9 +1732,8 @@ static enum scan_result collapse_scan_pm
 		if (folio_maybe_mapped_shared(folio)) {
 			if (++shared > max_ptes_shared) {
 				result = SCAN_EXCEED_SHARED_PTE;
-				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-				count_mthp_stat(HPAGE_PMD_ORDER,
-						MTHP_STAT_COLLAPSE_EXCEED_SHARED);
+				count_collapse_event(HPAGE_PMD_ORDER, THP_SCAN_EXCEED_SHARED_PTE,
+						     MTHP_STAT_COLLAPSE_EXCEED_SHARED);
 				goto out_unmap;
 			}
 		}
_

Patches currently in -mm which might be from [email protected] are

mm-khugepaged-refactor-per-scan-state-clearing-into-collapse_control_init_scan.patch
mm-khugepaged-extract-reference-check-into-folio_pte_referenced-helper.patch
mm-khugepaged-introduce-a-count_collapse_event-helper.patch
mm-khugepaged-fix-outdated-comments.patch
mm-khugepaged-refactor-the-pte-state-checks-into-a-helper.patch
mm-khugepaged-unmap-pte-before-releasing-vma-write-lock.patch
mm-documentation-clarify-where-the-mthp-stats-live.patch