[PATCH v4 2/7] mm/khugepaged: extract reference check into folio_pte_referenced() helper

["Nico Pache (Red Hat)" <nico.pache@linux.dev>]

This change deduplicates the "is this PTE/folio referenced enough to be
considered for a collapse" condition that was repeated in both
__collapse_huge_page_isolate() and collapse_scan_pmd(), extracting it into
a single inline helper function.

Also move the comment and use it as the function header. While we are at
it, updated the comment to clarify that a young pte is a recently accessed
one.

Acked-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Nico Pache (Red Hat) <nico.pache@linux.dev>
---
 mm/khugepaged.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1e26ea97381a..8babd4c97db6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -672,6 +672,22 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
 	}
 }
 
+/*
+ * folio_pte_referenced() - Check if a folio or its PTE mapping was recently used
+ *
+ * Return: true if recent access was observed through either the folio state
+ * or the current PTE mapping.
+ */
+static inline bool folio_pte_referenced(struct folio *folio,
+		struct vm_area_struct *vma, unsigned long addr, pte_t pteval)
+{
+	/* 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 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)
@@ -810,14 +826,8 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		if (folio_test_large(folio))
 			list_add_tail(&folio->lru, compound_pagelist);
 next:
-		/*
-		 * If collapse was initiated by khugepaged, check that there is
-		 * enough young pte to justify collapsing the page
-		 */
 		if (cc->is_khugepaged &&
-		    (pte_young(pteval) || folio_test_young(folio) ||
-		     folio_test_referenced(folio) ||
-		     mmu_notifier_test_young(vma->vm_mm, addr)))
+		    folio_pte_referenced(folio, vma, addr, pteval))
 			referenced++;
 	}
 
@@ -1766,14 +1776,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm,
 			goto out_unmap;
 		}
 
-		/*
-		 * If collapse was initiated by khugepaged, check that there is
-		 * enough young pte to justify collapsing the page
-		 */
 		if (cc->is_khugepaged &&
-		    (pte_young(pteval) || folio_test_young(folio) ||
-		     folio_test_referenced(folio) ||
-		     mmu_notifier_test_young(vma->vm_mm, addr)))
+		    folio_pte_referenced(folio, vma, addr, pteval))
 			referenced++;
 	}
 	if (cc->is_khugepaged &&

-- 
2.55.0