mm/balloon_compaction: make balloon page compaction callbacks static

Since commit b1123ea6 ("mm: balloon: use general non-lru movable page
feature"), these functions are called via balloon_aops callbacks. They're
not called directly outside this file. So make them static and clean up
the relevant code.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Link: https://lore.kernel.org/r/20220125132221.2220-1-linmiaohe@huawei.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>

include/linux/balloon_compaction.h

@@ -80,12 +80,6 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
 
 #ifdef CONFIG_BALLOON_COMPACTION
 extern const struct address_space_operations balloon_aops;
-extern bool balloon_page_isolate(struct page *page,
-				isolate_mode_t mode);
-extern void balloon_page_putback(struct page *page);
-extern int balloon_page_migrate(struct address_space *mapping,
-				struct page *newpage,
-				struct page *page, enum migrate_mode mode);
 
 /*
  * balloon_page_insert - insert a page into the balloon's page list and make
@@ -155,22 +149,6 @@ static inline void balloon_page_delete(struct page *page)
 	list_del(&page->lru);
 }
 
-static inline bool balloon_page_isolate(struct page *page)
-{
-	return false;
-}
-
-static inline void balloon_page_putback(struct page *page)
-{
-	return;
-}
-
-static inline int balloon_page_migrate(struct page *newpage,
-				struct page *page, enum migrate_mode mode)
-{
-	return 0;
-}
-
 static inline gfp_t balloon_mapping_gfp_mask(void)
 {
 	return GFP_HIGHUSER;

mm/balloon_compaction.c

@@ -203,7 +203,7 @@ EXPORT_SYMBOL_GPL(balloon_page_dequeue);
 
 #ifdef CONFIG_BALLOON_COMPACTION
 
-bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
+static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
 
 {
 	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
@@ -217,7 +217,7 @@ bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
 	return true;
 }
 
-void balloon_page_putback(struct page *page)
+static void balloon_page_putback(struct page *page)
 {
 	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 	unsigned long flags;
@@ -230,7 +230,7 @@ void balloon_page_putback(struct page *page)
 
 
 /* move_to_new_page() counterpart for a ballooned page */
-int balloon_page_migrate(struct address_space *mapping,
+static int balloon_page_migrate(struct address_space *mapping,
 		struct page *newpage, struct page *page,
 		enum migrate_mode mode)
 {