mm: Convert all PageMovable users to movable_operations

These drivers are rather uncomfortably hammered into the
address_space_operations hole.  They aren't filesystems and don't behave
like filesystems.  They just need their own movable_operations structure,
which we can point to directly from page->mapping.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

1 files changed, 51 insertions, 5 deletions

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 069a89e847f3..82c735ba6109 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -19,6 +19,43 @@ struct migration_target_control;
  */
 #define MIGRATEPAGE_SUCCESS		0
 
+/**
+ * struct movable_operations - Driver page migration
+ * @isolate_page:
+ * The VM calls this function to prepare the page to be moved.  The page
+ * is locked and the driver should not unlock it.  The driver should
+ * return ``true`` if the page is movable and ``false`` if it is not
+ * currently movable.  After this function returns, the VM uses the
+ * page->lru field, so the driver must preserve any information which
+ * is usually stored here.
+ *
+ * @migrate_page:
+ * After isolation, the VM calls this function with the isolated
+ * @src page.  The driver should copy the contents of the
+ * @src page to the @dst page and set up the fields of @dst page.
+ * Both pages are locked.
+ * If page migration is successful, the driver should call
+ * __ClearPageMovable(@src) and return MIGRATEPAGE_SUCCESS.
+ * If the driver cannot migrate the page at the moment, it can return
+ * -EAGAIN.  The VM interprets this as a temporary migration failure and
+ * will retry it later.  Any other error value is a permanent migration
+ * failure and migration will not be retried.
+ * The driver shouldn't touch the @src->lru field while in the
+ * migrate_page() function.  It may write to @dst->lru.
+ *
+ * @putback_page:
+ * If migration fails on the isolated page, the VM informs the driver
+ * that the page is no longer a candidate for migration by calling
+ * this function.  The driver should put the isolated page back into
+ * its own data structure.
+ */
+struct movable_operations {
+	bool (*isolate_page)(struct page *, isolate_mode_t);
+	int (*migrate_page)(struct page *dst, struct page *src,
+			enum migrate_mode);
+	void (*putback_page)(struct page *);
+};
+
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
@@ -91,13 +128,13 @@ static inline int next_demotion_node(int node)
 #endif
 
 #ifdef CONFIG_COMPACTION
-extern int PageMovable(struct page *page);
-extern void __SetPageMovable(struct page *page, struct address_space *mapping);
-extern void __ClearPageMovable(struct page *page);
+bool PageMovable(struct page *page);
+void __SetPageMovable(struct page *page, const struct movable_operations *ops);
+void __ClearPageMovable(struct page *page);
 #else
-static inline int PageMovable(struct page *page) { return 0; }
+static inline bool PageMovable(struct page *page) { return false; }
 static inline void __SetPageMovable(struct page *page,
-				struct address_space *mapping)
+		const struct movable_operations *ops)
 {
 }
 static inline void __ClearPageMovable(struct page *page)
@@ -110,6 +147,15 @@ static inline bool folio_test_movable(struct folio *folio)
 	return PageMovable(&folio->page);
 }
 
+static inline
+const struct movable_operations *page_movable_ops(struct page *page)
+{
+	VM_BUG_ON(!__PageMovable(page));
+
+	return (const struct movable_operations *)
+		((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE);
+}
+
 #ifdef CONFIG_NUMA_BALANCING
 extern int migrate_misplaced_page(struct page *page,
 				  struct vm_area_struct *vma, int node);