mm/migrate: remove MIGRATEPAGE_UNMAP

[ Upstream commit 95c2908f1a4fd608b1cdbb5acef3572e5d769e1c ]

migrate_folio_unmap() is the only user of MIGRATEPAGE_UNMAP.  We want to
remove MIGRATEPAGE_* completely.

It's rather weird to have a generic MIGRATEPAGE_UNMAP, documented to be
returned from address-space callbacks, when it's only used for an internal
helper.

Let's start by having only a single "success" return value for
migrate_folio_unmap() -- 0 -- by moving the "folio was already freed"
check into the single caller.

There is a remaining comment for PG_isolated, which we renamed to
PG_movable_ops_isolated recently and forgot to update.

While we might still run into that case with zsmalloc, it's something we
want to get rid of soon.  So let's just focus that optimization on real
folios only for now by excluding movable_ops pages.  Note that concurrent
freeing can happen at any time and this "already freed" check is not
relevant for correctness.

[[email protected]: no need to pass "reason" to migrate_folio_unmap(), per Lance]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Lance Yang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Benjamin LaHaise <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Dave Kleikamp <[email protected]>
Cc: David Sterba <[email protected]>
Cc: Eugenio Pé rez <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Jerrin Shaji George <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mathew Brost <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Cc: Dave Kleikamp <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Stable-dep-of: 4ba5a8a7faa6 ("vmw_balloon: indicate success when effectively deflating during migration")
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: davidhildenbrand

include/linux/migrate.h

@@ -18,7 +18,6 @@ struct migration_target_control;
  * - zero on page migration success;
  */
 #define MIGRATEPAGE_SUCCESS		0
-#define MIGRATEPAGE_UNMAP		1
 
 /**
  * struct movable_operations - Driver page migration

mm/migrate.c

@@ -1189,7 +1189,7 @@ static void migrate_folio_done(struct folio *src,
 static int migrate_folio_unmap(new_folio_t get_new_folio,
 		free_folio_t put_new_folio, unsigned long private,
 		struct folio *src, struct folio **dstp, enum migrate_mode mode,
-		enum migrate_reason reason, struct list_head *ret)
+		struct list_head *ret)
 {
 	struct folio *dst;
 	int rc = -EAGAIN;
@@ -1198,16 +1198,6 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 	bool locked = false;
 	bool dst_locked = false;
 
-	if (folio_ref_count(src) == 1) {
-		/* Folio was freed from under us. So we are done. */
-		folio_clear_active(src);
-		folio_clear_unevictable(src);
-		/* free_pages_prepare() will clear PG_isolated. */
-		list_del(&src->lru);
-		migrate_folio_done(src, reason);
-		return MIGRATEPAGE_SUCCESS;
-	}
-
 	dst = get_new_folio(src, private);
 	if (!dst)
 		return -ENOMEM;
@@ -1297,7 +1287,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 
 	if (unlikely(page_has_movable_ops(&src->page))) {
 		__migrate_folio_record(dst, old_page_state, anon_vma);
-		return MIGRATEPAGE_UNMAP;
+		return 0;
 	}
 
 	/*
@@ -1327,7 +1317,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
 
 	if (!folio_mapped(src)) {
 		__migrate_folio_record(dst, old_page_state, anon_vma);
-		return MIGRATEPAGE_UNMAP;
+		return 0;
 	}
 
 out:
@@ -1870,14 +1860,27 @@ static int migrate_pages_batch(struct list_head *from,
 				continue;
 			}
 
+			/*
+			 * If we are holding the last folio reference, the folio
+			 * was freed from under us, so just drop our reference.
+			 */
+			if (likely(!page_has_movable_ops(&folio->page)) &&
+			    folio_ref_count(folio) == 1) {
+				folio_clear_active(folio);
+				folio_clear_unevictable(folio);
+				list_del(&folio->lru);
+				migrate_folio_done(folio, reason);
+				stats->nr_succeeded += nr_pages;
+				stats->nr_thp_succeeded += is_thp;
+				continue;
+			}
+
 			rc = migrate_folio_unmap(get_new_folio, put_new_folio,
-					private, folio, &dst, mode, reason,
-					ret_folios);
+					private, folio, &dst, mode, ret_folios);
 			/*
 			 * The rules are:
-			 *	Success: folio will be freed
-			 *	Unmap: folio will be put on unmap_folios list,
-			 *	       dst folio put on dst_folios list
+			 *	0: folio will be put on unmap_folios list,
+			 *	   dst folio put on dst_folios list
 			 *	-EAGAIN: stay on the from list
 			 *	-ENOMEM: stay on the from list
 			 *	Other errno: put on ret_folios list
@@ -1927,11 +1930,7 @@ static int migrate_pages_batch(struct list_head *from,
 				thp_retry += is_thp;
 				nr_retry_pages += nr_pages;
 				break;
-			case MIGRATEPAGE_SUCCESS:
-				stats->nr_succeeded += nr_pages;
-				stats->nr_thp_succeeded += is_thp;
-				break;
-			case MIGRATEPAGE_UNMAP:
+			case 0:
 				list_move_tail(&folio->lru, &unmap_folios);
 				list_add_tail(&dst->lru, &dst_folios);
 				break;