linux-kernel - [PATCH V2 3/5] mm/khugepaged: change collapse_pte_mapped

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Message-ID: <20251224111351.41042-10-shivankg@amd.com>
Date: Wed, 24 Dec 2025 11:13:55 +0000
From: Shivank Garg <shivankg@....com>
To: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand
	<david@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
CC: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
	<baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <shivankg@....com>
Subject: [PATCH V2 3/5] mm/khugepaged: change collapse_pte_mapped_thp() to return void

The only external caller of collapse_pte_mapped_thp() is uprobe, which
ignores the return value. Change the external API to return void to
simplify the interface.

Introduce try_collapse_pte_mapped_thp() for internal use that preserves
the return value. This prepares for future patch that will convert
the return type to use enum scan_result.

Suggested-by: David Hildenbrand (Red Hat) <david@...nel.org>
Signed-off-by: Shivank Garg <shivankg@....com>
---
 include/linux/khugepaged.h |  9 ++++-----
 mm/khugepaged.c            | 40 ++++++++++++++++++++++----------------
 2 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index eb1946a70cff..37b992b22bba 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -17,8 +17,8 @@ extern void khugepaged_enter_vma(struct vm_area_struct *vma,
 				 vm_flags_t vm_flags);
 extern void khugepaged_min_free_kbytes_update(void);
 extern bool current_is_khugepaged(void);
-extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
-				   bool install_pmd);
+extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
+				    bool install_pmd);
 
 static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
@@ -42,10 +42,9 @@ static inline void khugepaged_enter_vma(struct vm_area_struct *vma,
 					vm_flags_t vm_flags)
 {
 }
-static inline int collapse_pte_mapped_thp(struct mm_struct *mm,
-					  unsigned long addr, bool install_pmd)
+static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
+					   unsigned long addr, bool install_pmd)
 {
-	return 0;
 }
 
 static inline void khugepaged_min_free_kbytes_update(void)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0b549c3250f9..04ff0730c9a1 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1477,20 +1477,8 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
 	return SCAN_SUCCEED;
 }
 
-/**
- * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
- * address haddr.
- *
- * @mm: process address space where collapse happens
- * @addr: THP collapse address
- * @install_pmd: If a huge PMD should be installed
- *
- * This function checks whether all the PTEs in the PMD are pointing to the
- * right THP. If so, retract the page table so the THP can refault in with
- * as pmd-mapped. Possibly install a huge PMD mapping the THP.
- */
-int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
-			    bool install_pmd)
+static int try_collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
+				       bool install_pmd)
 {
 	int nr_mapped_ptes = 0, result = SCAN_FAIL;
 	unsigned int nr_batch_ptes;
@@ -1711,6 +1699,24 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
 	return result;
 }
 
+/**
+ * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
+ * address haddr.
+ *
+ * @mm: process address space where collapse happens
+ * @addr: THP collapse address
+ * @install_pmd: If a huge PMD should be installed
+ *
+ * This function checks whether all the PTEs in the PMD are pointing to the
+ * right THP. If so, retract the page table so the THP can refault in with
+ * as pmd-mapped. Possibly install a huge PMD mapping the THP.
+ */
+void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
+			     bool install_pmd)
+{
+	try_collapse_pte_mapped_thp(mm, addr, install_pmd);
+}
+
 /* Can we retract page tables for this file-backed VMA? */
 static bool file_backed_vma_is_retractable(struct vm_area_struct *vma)
 {
@@ -2227,7 +2233,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 
 	/*
 	 * Remove pte page tables, so we can re-fault the page as huge.
-	 * If MADV_COLLAPSE, adjust result to call collapse_pte_mapped_thp().
+	 * If MADV_COLLAPSE, adjust result to call try_collapse_pte_mapped_thp().
 	 */
 	retract_page_tables(mapping, start);
 	if (cc && !cc->is_khugepaged)
@@ -2479,7 +2485,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
 					mmap_read_lock(mm);
 					if (hpage_collapse_test_exit_or_disable(mm))
 						goto breakouterloop;
-					*result = collapse_pte_mapped_thp(mm,
+					*result = try_collapse_pte_mapped_thp(mm,
 						khugepaged_scan.address, false);
 					if (*result == SCAN_PMD_MAPPED)
 						*result = SCAN_SUCCEED;
@@ -2869,7 +2875,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 		case SCAN_PTE_MAPPED_HUGEPAGE:
 			BUG_ON(mmap_locked);
 			mmap_read_lock(mm);
-			result = collapse_pte_mapped_thp(mm, addr, true);
+			result = try_collapse_pte_mapped_thp(mm, addr, true);
 			mmap_read_unlock(mm);
 			goto handle_result;
 		/* Whitelisted set of results where continuing OK */
-- 
2.43.0