Re: [PATCH v4 0/7] mm/khugepaged: several cleanups

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 11 Aug 2026 06:48:32 -0600 "Nico Pache (Red Hat)" <nico.pache@linux.dev> wrote:

> The following changes stem from a number of reviews during my khugepaged
> mTHP support series [1]. Some of these are minor code cleanups, issues or
> reviews that we decided to deferred to a followup series, or in the case
> of the more major patch of the series, changes [2] Lance Yang attempted
> while my series was in-flight and we decided to wait till later to try.

Thanks, I've updated mm.git's mm-unstable branch to this version.

> Changes in v4:
>  - Add Acks/RB tags
>  - [patch2] rename pte_is_referenced() to folio_pte_referenced()
>  - [patch2] keep cc->is_khugepaged out of the helper gate
>  - [patch2] simplify/clarify the helper comment

Here's how v4 altered mm.git:


 mm/khugepaged.c |   27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

--- a/mm/khugepaged.c~b
+++ a/mm/khugepaged.c
@@ -693,20 +693,19 @@ static void release_pte_pages(pte_t *pte
 }
 
 /*
- * pte_is_referenced() - Check for enough referenced PTEs to justify collapsing
+ * folio_pte_referenced() - Check if a folio or its PTE mapping was recently used
  *
- * If collapse was initiated by khugepaged, check that the page has been
- * recently accessed (young pte) to justify collapsing the page.
- *
- * Return: true if the page has been recently accessed.
+ * Return: true if recent access was observed through either the folio state
+ * or the current PTE mapping.
  */
-static inline bool pte_is_referenced(struct collapse_control *cc, pte_t pteval,
-	struct folio *folio, struct vm_area_struct *vma, unsigned long addr)
+static inline bool folio_pte_referenced(struct folio *folio,
+		struct vm_area_struct *vma, unsigned long addr, pte_t pteval)
 {
-	return cc->is_khugepaged &&
-	       (pte_young(pteval) || folio_test_young(folio) ||
-		folio_test_referenced(folio) ||
-		mmu_notifier_test_young(vma->vm_mm, addr));
+	/* The folio was referenced previously ... */
+	if (folio_test_young(folio) || folio_test_referenced(folio))
+		return true;
+	/* ... or the PTE mapping was recently used */
+	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,
@@ -910,7 +909,8 @@ static enum scan_result __collapse_huge_
 		if (folio_test_large(folio))
 			list_add_tail(&folio->lru, compound_pagelist);
 next:
-		if (pte_is_referenced(cc, pteval, folio, vma, addr))
+		if (cc->is_khugepaged &&
+		    folio_pte_referenced(folio, vma, addr, pteval))
 			referenced++;
 	}
 
@@ -1790,7 +1790,8 @@ static enum scan_result collapse_scan_pm
 			goto out_unmap;
 		}
 
-		if (pte_is_referenced(cc, pteval, folio, vma, addr))
+		if (cc->is_khugepaged &&
+		    folio_pte_referenced(folio, vma, addr, pteval))
 			referenced++;
 	}
 	if (cc->is_khugepaged &&
_