mm/khugepaged: unify SCAN_PMD_NONE and SCAN_PMD_NULL into SCAN_NO_PTE_TABLE

The current hugepage collapse scan results include two separate values,
SCAN_PMD_NONE and SCAN_PMD_NULL, which are handled identically by the
consuming code.

To reduce confusion and improve long-term maintenance, this commit merges
these two functionally equivalent states into a single, clearer
identifier: SCAN_NO_PTE_TABLE

Link: https://lkml.kernel.org/r/20251114030028.7035-4-richard.weiyang@gmail.com
Suggested-by: "David Hildenbrand (Red Hat)" <david@kernel.org>
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Nico Pache <npache@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 13 deletions

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 2ee5048b764e..40f9d5939aa5 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -30,8 +30,7 @@
 enum scan_result {
 	SCAN_FAIL,
 	SCAN_SUCCEED,
-	SCAN_PMD_NULL,
-	SCAN_PMD_NONE,
+	SCAN_NO_PTE_TABLE,
 	SCAN_PMD_MAPPED,
 	SCAN_EXCEED_NONE_PTE,
 	SCAN_EXCEED_SWAP_PTE,
@@ -934,7 +933,7 @@ static inline int check_pmd_state(pmd_t *pmd)
 	pmd_t pmde = pmdp_get_lockless(pmd);
 
 	if (pmd_none(pmde))
-		return SCAN_PMD_NONE;
+		return SCAN_NO_PTE_TABLE;
 
 	/*
 	 * The folio may be under migration when khugepaged is trying to
@@ -944,11 +943,11 @@ static inline int check_pmd_state(pmd_t *pmd)
 	if (pmd_is_migration_entry(pmde))
 		return SCAN_PMD_MAPPED;
 	if (!pmd_present(pmde))
-		return SCAN_PMD_NULL;
+		return SCAN_NO_PTE_TABLE;
 	if (pmd_trans_huge(pmde))
 		return SCAN_PMD_MAPPED;
 	if (pmd_bad(pmde))
-		return SCAN_PMD_NULL;
+		return SCAN_NO_PTE_TABLE;
 	return SCAN_SUCCEED;
 }
 
@@ -958,7 +957,7 @@ static int find_pmd_or_thp_or_none(struct mm_struct *mm,
 {
 	*pmd = mm_find_pmd(mm, address);
 	if (!*pmd)
-		return SCAN_PMD_NULL;
+		return SCAN_NO_PTE_TABLE;
 
 	return check_pmd_state(*pmd);
 }
@@ -1013,7 +1012,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
 			pte = pte_offset_map_ro_nolock(mm, pmd, addr, &ptl);
 			if (!pte) {
 				mmap_read_unlock(mm);
-				result = SCAN_PMD_NULL;
+				result = SCAN_NO_PTE_TABLE;
 				goto out;
 			}
 		}
@@ -1187,7 +1186,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 						      &compound_pagelist);
 		spin_unlock(pte_ptl);
 	} else {
-		result = SCAN_PMD_NULL;
+		result = SCAN_NO_PTE_TABLE;
 	}
 
 	if (unlikely(result != SCAN_SUCCEED)) {
@@ -1270,7 +1269,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 	nodes_clear(cc->alloc_nmask);
 	pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl);
 	if (!pte) {
-		result = SCAN_PMD_NULL;
+		result = SCAN_NO_PTE_TABLE;
 		goto out;
 	}
 
@@ -1544,8 +1543,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
 	switch (result) {
 	case SCAN_SUCCEED:
 		break;
-	case SCAN_PMD_NULL:
-	case SCAN_PMD_NONE:
+	case SCAN_NO_PTE_TABLE:
 		/*
 		 * All pte entries have been removed and pmd cleared.
 		 * Skip all the pte checks and just update the pmd mapping.
@@ -2832,8 +2830,7 @@ handle_result:
 			mmap_read_unlock(mm);
 			goto handle_result;
 		/* Whitelisted set of results where continuing OK */
-		case SCAN_PMD_NULL:
-		case SCAN_PMD_NONE:
+		case SCAN_NO_PTE_TABLE:
 		case SCAN_PTE_NON_PRESENT:
 		case SCAN_PTE_UFFD_WP:
 		case SCAN_LACK_REFERENCED_PAGE: