linux-kernel - [PATCH V4 1/2] mm: add folio_migration_expected

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Message-ID: <20250422114000.15003-2-shivankg@amd.com>
Date: Tue, 22 Apr 2025 11:40:03 +0000
From: Shivank Garg <shivankg@....com>
To: <shaggy@...nel.org>, <akpm@...ux-foundation.org>
CC: <willy@...radead.org>, <shivankg@....com>, <david@...hat.com>,
	<wangkefeng.wang@...wei.com>, <jane.chu@...cle.com>, <ziy@...dia.com>,
	<donettom@...ux.ibm.com>, <apopple@...dia.com>,
	<jfs-discussion@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <syzbot+8bb6fd945af4e0ad9299@...kaller.appspotmail.com>
Subject: [PATCH V4 1/2] mm: add folio_migration_expected_refs() as inline function

Rename the previously static folio_expected_refs() to clarify its
purpose and scope, making it an inline function
folio_migration_expected_refs() to calculate expected folio references
during migration. The function is only suitable for folios unmapped from
page tables.

Signed-off-by: Shivank Garg <shivankg@....com>
---
 include/linux/migrate.h | 26 ++++++++++++++++++++++++++
 mm/migrate.c            | 22 ++++------------------
 2 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6..083293a6d261 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -60,6 +60,32 @@ struct movable_operations {
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
+/**
+ * folio_migrate_expected_refs - Count expected references for an unmapped folio.
+ * @mapping: The address space the folio belongs to.
+ * @folio: The folio to check.
+ *
+ * Calculate the expected reference count for a folio during migration.
+ * This function is only suitable for folios that are unmapped from page tables
+ * (i.e., no references from page table mappings: !folio_mapped()).
+ *
+ * Return: The expected reference count
+ */
+static inline int folio_migration_expected_refs(struct address_space *mapping,
+		struct folio *folio)
+{
+	int refs = 1;
+
+	if (!mapping)
+		return refs;
+
+	refs += folio_nr_pages(folio);
+	if (folio_test_private(folio))
+		refs++;
+
+	return refs;
+}
+
 #ifdef CONFIG_MIGRATION
 
 void putback_movable_pages(struct list_head *l);
diff --git a/mm/migrate.c b/mm/migrate.c
index 6e2488e5dbe4..6c785abce90e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,20 +445,6 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
-		struct folio *folio)
-{
-	int refs = 1;
-	if (!mapping)
-		return refs;
-
-	refs += folio_nr_pages(folio);
-	if (folio_test_private(folio))
-		refs++;
-
-	return refs;
-}
-
 /*
  * Replace the folio in the mapping.
  *
@@ -601,7 +587,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
 int folio_migrate_mapping(struct address_space *mapping,
 		struct folio *newfolio, struct folio *folio, int extra_count)
 {
-	int expected_count = folio_expected_refs(mapping, folio) + extra_count;
+	int expected_count = folio_migration_expected_refs(mapping, folio) + extra_count;
 
 	if (folio_ref_count(folio) != expected_count)
 		return -EAGAIN;
@@ -618,7 +604,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 				   struct folio *dst, struct folio *src)
 {
 	XA_STATE(xas, &mapping->i_pages, folio_index(src));
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_migration_expected_refs(mapping, src);
 
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
@@ -749,7 +735,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 			   struct folio *src, void *src_private,
 			   enum migrate_mode mode)
 {
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_migration_expected_refs(mapping, src);
 
 	/* Check whether src does not have extra refs before we do more work */
 	if (folio_ref_count(src) != expected_count)
@@ -837,7 +823,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		return migrate_folio(mapping, dst, src, mode);
 
 	/* Check whether page does not have extra refs before we do more work */
-	expected_count = folio_expected_refs(mapping, src);
+	expected_count = folio_migration_expected_refs(mapping, src);
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 
-- 
2.34.1