+ mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper.patch added to mm-new branch

+ mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/khugepaged: merge PTE scanning logic into a new helper
has been added to the -mm mm-new branch.  Its filename is
     mm-khugepaged-merge-pte-scanning-logic-into-a-new-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-merge-pte-scanning-logic-into-a-new-helper.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Lance Yang <lance.yang@linux.dev>
Subject: mm/khugepaged: merge PTE scanning logic into a new helper
Date: Wed, 8 Oct 2025 12:37:48 +0800

As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
and __collapse_huge_page_isolate() was almost duplicated.

This patch cleans things up by moving all the common PTE checking logic
into a new shared helper, thp_collapse_check_pte().  While at it, we use
vm_normal_folio() instead of vm_normal_page().

Link: https://lkml.kernel.org/r/20251008043748.45554-4-lance.yang@linux.dev
Signed-off-by: Lance Yang <lance.yang@linux.dev>
Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Dev Jain <dev.jain@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/khugepaged.c |  243 ++++++++++++++++++++++++----------------------
 1 file changed, 130 insertions(+), 113 deletions(-)

--- a/mm/khugepaged.c~mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper
+++ a/mm/khugepaged.c
@@ -61,6 +61,12 @@ enum scan_result {
 	SCAN_PAGE_FILLED,
 };
 
+enum pte_check_result {
+	PTE_CHECK_SUCCEED,
+	PTE_CHECK_CONTINUE,
+	PTE_CHECK_FAIL,
+};
+
 #define CREATE_TRACE_POINTS
 #include <trace/events/huge_memory.h>
 
@@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte
 	}
 }
 
+/*
+ * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
+ * @pte:           The PTE to check
+ * @vma:           The VMA the PTE belongs to
+ * @addr:          The virtual address corresponding to this PTE
+ * @foliop:        On success, used to return a pointer to the folio
+ *                 Must be non-NULL
+ * @none_or_zero:  Counter for none/zero PTEs. Must be non-NULL
+ * @unmapped:      Counter for swap PTEs. Can be NULL if not scanning swaps
+ * @shared:        Counter for shared pages. Must be non-NULL
+ * @scan_result:   Used to return the failure reason (SCAN_*) on a
+ *                 PTE_CHECK_FAIL return. Must be non-NULL
+ * @cc:            Collapse control settings
+ *
+ * Returns:
+ *   PTE_CHECK_SUCCEED  - PTE is suitable, proceed with further checks
+ *   PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
+ *   PTE_CHECK_FAIL     - Abort collapse scan
+ */
+static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
+		unsigned long addr, struct folio **foliop, int *none_or_zero,
+		int *unmapped, int *shared, int *scan_result,
+		struct collapse_control *cc)
+{
+	struct folio *folio = NULL;
+
+	if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
+		(*none_or_zero)++;
+		if (!userfaultfd_armed(vma) &&
+		    (!cc->is_khugepaged ||
+		     *none_or_zero <= khugepaged_max_ptes_none)) {
+			return PTE_CHECK_CONTINUE;
+		} else {
+			*scan_result = SCAN_EXCEED_NONE_PTE;
+			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+			return PTE_CHECK_FAIL;
+		}
+	} else if (!pte_present(pte)) {
+		if (!unmapped) {
+			*scan_result = SCAN_PTE_NON_PRESENT;
+			return PTE_CHECK_FAIL;
+		}
+
+		if (non_swap_entry(pte_to_swp_entry(pte))) {
+			*scan_result = SCAN_PTE_NON_PRESENT;
+			return PTE_CHECK_FAIL;
+		}
+
+		(*unmapped)++;
+		if (!cc->is_khugepaged ||
+		    *unmapped <= khugepaged_max_ptes_swap) {
+			/*
+			 * Always be strict with uffd-wp enabled swap
+			 * entries. Please see comment below for
+			 * pte_uffd_wp().
+			 */
+			if (pte_swp_uffd_wp(pte)) {
+				*scan_result = SCAN_PTE_UFFD_WP;
+				return PTE_CHECK_FAIL;
+			}
+			return PTE_CHECK_CONTINUE;
+		} else {
+			*scan_result = SCAN_EXCEED_SWAP_PTE;
+			count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
+			return PTE_CHECK_FAIL;
+		}
+	} else if (pte_uffd_wp(pte)) {
+		/*
+		 * Don't collapse the page if any of the small PTEs are
+		 * armed with uffd write protection. Here we can also mark
+		 * the new huge pmd as write protected if any of the small
+		 * ones is marked but that could bring unknown userfault
+		 * messages that falls outside of the registered range.
+		 * So, just be simple.
+		 */
+		*scan_result = SCAN_PTE_UFFD_WP;
+		return PTE_CHECK_FAIL;
+	}
+
+	folio = vm_normal_folio(vma, addr, pte);
+	if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
+		*scan_result = SCAN_PAGE_NULL;
+		return PTE_CHECK_FAIL;
+	}
+
+	if (!folio_test_anon(folio)) {
+		VM_WARN_ON_FOLIO(true, folio);
+		*scan_result = SCAN_PAGE_ANON;
+		return PTE_CHECK_FAIL;
+	}
+
+	/*
+	 * We treat a single page as shared if any part of the THP
+	 * is shared.
+	 */
+	if (folio_maybe_mapped_shared(folio)) {
+		(*shared)++;
+		if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
+			*scan_result = SCAN_EXCEED_SHARED_PTE;
+			count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
+			return PTE_CHECK_FAIL;
+		}
+	}
+
+	*foliop = folio;
+
+	return PTE_CHECK_SUCCEED;
+}
+
 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 					unsigned long start_addr,
 					pte_t *pte,
 					struct collapse_control *cc,
 					struct list_head *compound_pagelist)
 {
-	struct page *page = NULL;
 	struct folio *folio = NULL;
 	unsigned long addr = start_addr;
 	pte_t *_pte;
 	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
+	int pte_check_res;
 
 	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
 	     _pte++, addr += PAGE_SIZE) {
 		pte_t pteval = ptep_get(_pte);
-		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
-			++none_or_zero;
-			if (!userfaultfd_armed(vma) &&
-			    (!cc->is_khugepaged ||
-			     none_or_zero <= khugepaged_max_ptes_none)) {
-				continue;
-			} else {
-				result = SCAN_EXCEED_NONE_PTE;
-				count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
-				goto out;
-			}
-		} else if (!pte_present(pteval)) {
-			result = SCAN_PTE_NON_PRESENT;
-			goto out;
-		} else if (pte_uffd_wp(pteval)) {
-			result = SCAN_PTE_UFFD_WP;
-			goto out;
-		}
-		page = vm_normal_page(vma, addr, pteval);
-		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
-			result = SCAN_PAGE_NULL;
-			goto out;
-		}
 
-		folio = page_folio(page);
-		if (!folio_test_anon(folio)) {
-			VM_WARN_ON_FOLIO(true, folio);
-			result = SCAN_PAGE_ANON;
-			goto out;
-		}
+		pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
+					&folio, &none_or_zero, NULL, &shared,
+					&result, cc);
 
-		/* See hpage_collapse_scan_pmd(). */
-		if (folio_maybe_mapped_shared(folio)) {
-			++shared;
-			if (cc->is_khugepaged &&
-			    shared > khugepaged_max_ptes_shared) {
-				result = SCAN_EXCEED_SHARED_PTE;
-				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-				goto out;
-			}
-		}
+		if (pte_check_res == PTE_CHECK_CONTINUE)
+			continue;
+		else if (pte_check_res == PTE_CHECK_FAIL)
+			goto out;
 
 		if (folio_test_large(folio)) {
 			struct folio *f;
@@ -1264,11 +1347,11 @@ static int hpage_collapse_scan_pmd(struc
 	pte_t *pte, *_pte;
 	int result = SCAN_FAIL, referenced = 0;
 	int none_or_zero = 0, shared = 0;
-	struct page *page = NULL;
 	struct folio *folio = NULL;
 	unsigned long addr;
 	spinlock_t *ptl;
 	int node = NUMA_NO_NODE, unmapped = 0;
+	int pte_check_res;
 
 	VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK);
 
@@ -1287,81 +1370,15 @@ static int hpage_collapse_scan_pmd(struc
 	for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR;
 	     _pte++, addr += PAGE_SIZE) {
 		pte_t pteval = ptep_get(_pte);
-		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
-			++none_or_zero;
-			if (!userfaultfd_armed(vma) &&
-			    (!cc->is_khugepaged ||
-			     none_or_zero <= khugepaged_max_ptes_none)) {
-				continue;
-			} else {
-				result = SCAN_EXCEED_NONE_PTE;
-				count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
-				goto out_unmap;
-			}
-		} else if (!pte_present(pteval)) {
-			if (non_swap_entry(pte_to_swp_entry(pteval))) {
-				result = SCAN_PTE_NON_PRESENT;
-				goto out_unmap;
-			}
 
-			++unmapped;
-			if (!cc->is_khugepaged ||
-			    unmapped <= khugepaged_max_ptes_swap) {
-				/*
-				 * Always be strict with uffd-wp
-				 * enabled swap entries.  Please see
-				 * comment below for pte_uffd_wp().
-				 */
-				if (pte_swp_uffd_wp(pteval)) {
-					result = SCAN_PTE_UFFD_WP;
-					goto out_unmap;
-				}
-				continue;
-			} else {
-				result = SCAN_EXCEED_SWAP_PTE;
-				count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
-				goto out_unmap;
-			}
-		} else if (pte_uffd_wp(pteval)) {
-			/*
-			 * Don't collapse the page if any of the small
-			 * PTEs are armed with uffd write protection.
-			 * Here we can also mark the new huge pmd as
-			 * write protected if any of the small ones is
-			 * marked but that could bring unknown
-			 * userfault messages that falls outside of
-			 * the registered range.  So, just be simple.
-			 */
-			result = SCAN_PTE_UFFD_WP;
-			goto out_unmap;
-		}
-
-		page = vm_normal_page(vma, addr, pteval);
-		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
-			result = SCAN_PAGE_NULL;
-			goto out_unmap;
-		}
-		folio = page_folio(page);
+		pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
+					&folio, &none_or_zero, &unmapped,
+					&shared, &result, cc);
 
-		if (!folio_test_anon(folio)) {
-			VM_WARN_ON_FOLIO(true, folio);
-			result = SCAN_PAGE_ANON;
+		if (pte_check_res == PTE_CHECK_CONTINUE)
+			continue;
+		else if (pte_check_res == PTE_CHECK_FAIL)
 			goto out_unmap;
-		}
-
-		/*
-		 * We treat a single page as shared if any part of the THP
-		 * is shared.
-		 */
-		if (folio_maybe_mapped_shared(folio)) {
-			++shared;
-			if (cc->is_khugepaged &&
-			    shared > khugepaged_max_ptes_shared) {
-				result = SCAN_EXCEED_SHARED_PTE;
-				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
-				goto out_unmap;
-			}
-		}
 
 		/*
 		 * Record which node the original page is from and save this
_

Patches currently in -mm which might be from lance.yang@linux.dev are

hung_task-fix-warnings-caused-by-unaligned-lock-pointers.patch
mm-khugepaged-abort-collapse-scan-on-non-swap-entries.patch
mm-khugepaged-optimize-pte-scanning-with-if-else-if-else-if-chain.patch
mm-khugepaged-use-vm_warn_on_folio-instead-of-vm_bug_on_folio-for-non-anon-folios.patch
mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper.patch