[PATCH RFC 07/29] mm/migrate: rename isolate_movable_page() to isolate_movable_ops_page()

[David Hildenbrand]

... and start moving back to per-page things that will absolutely not be
folio things in the future. Add documentation and a comment that the
remaining folio stuff (lock, refcount) will have to be reworked as well.

While at it, convert the VM_BUG_ON() into a WARN_ON_ONCE() and handle
it gracefully (relevant with further changes), and convert a
WARN_ON_ONCE() into a VM_WARN_ON_ONCE_PAGE().

Signed-off-by: David Hildenbrand <david at redhat.com>
---
 include/linux/migrate.h |  4 ++--
 mm/compaction.c         |  2 +-
 mm/migrate.c            | 39 +++++++++++++++++++++++++++++----------
 3 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6d..c0ec7422837bd 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -69,7 +69,7 @@ int migrate_pages(struct list_head *l, new_folio_t new, free_folio_t free,
 		  unsigned long private, enum migrate_mode mode, int reason,
 		  unsigned int *ret_succeeded);
 struct folio *alloc_migration_target(struct folio *src, unsigned long private);
-bool isolate_movable_page(struct page *page, isolate_mode_t mode);
+bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode);
 bool isolate_folio_to_list(struct folio *folio, struct list_head *list);
 
 int migrate_huge_page_move_mapping(struct address_space *mapping,
@@ -90,7 +90,7 @@ static inline int migrate_pages(struct list_head *l, new_folio_t new,
 static inline struct folio *alloc_migration_target(struct folio *src,
 		unsigned long private)
 	{ return NULL; }
-static inline bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+static inline bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
 	{ return false; }
 static inline bool isolate_folio_to_list(struct folio *folio, struct list_head *list)
 	{ return false; }
diff --git a/mm/compaction.c b/mm/compaction.c
index 3925cb61dbb8f..17455c5a4be05 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1093,7 +1093,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 					locked = NULL;
 				}
 
-				if (isolate_movable_page(page, mode)) {
+				if (isolate_movable_ops_page(page, mode)) {
 					folio = page_folio(page);
 					goto isolate_success;
 				}
diff --git a/mm/migrate.c b/mm/migrate.c
index ea8c74d996592..6bbb455f8b593 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -51,8 +51,26 @@
 #include "internal.h"
 #include "swap.h"
 
-bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+/**
+ * isolate_movable_ops_page - isolate a movable_ops page for migration
+ * @page: The page.
+ * @mode: The isolation mode.
+ *
+ * Try to isolate a movable_ops page for migration. Will fail if the page is
+ * not a movable_ops page, if the page is already isolated for migration
+ * or if the page was just was released by its owner.
+ *
+ * Once isolated, the page cannot get freed until it is either putback
+ * or migrated.
+ *
+ * Returns true if isolation succeeded, otherwise false.
+ */
+bool isolate_movable_ops_page(struct page *page, isolate_mode_t mode)
 {
+	/*
+	 * TODO: these pages will not be folios in the future. All
+	 * folio dependencies will have to be removed.
+	 */
 	struct folio *folio = folio_get_nontail_page(page);
 	const struct movable_operations *mops;
 
@@ -73,7 +91,7 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	 * we use non-atomic bitops on newly allocated page flags so
 	 * unconditionally grabbing the lock ruins page's owner side.
 	 */
-	if (unlikely(!__folio_test_movable(folio)))
+	if (unlikely(!__PageMovable(page)))
 		goto out_putfolio;
 
 	/*
@@ -90,18 +108,19 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	if (unlikely(!folio_trylock(folio)))
 		goto out_putfolio;
 
-	if (!folio_test_movable(folio) || folio_test_isolated(folio))
+	if (!PageMovable(page) || PageIsolated(page))
 		goto out_no_isolated;
 
-	mops = folio_movable_ops(folio);
-	VM_BUG_ON_FOLIO(!mops, folio);
+	mops = page_movable_ops(page);
+	if (WARN_ON_ONCE(!mops))
+		goto out_no_isolated;
 
-	if (!mops->isolate_page(&folio->page, mode))
+	if (!mops->isolate_page(page, mode))
 		goto out_no_isolated;
 
 	/* Driver shouldn't use the isolated flag */
-	WARN_ON_ONCE(folio_test_isolated(folio));
-	folio_set_isolated(folio);
+	VM_WARN_ON_ONCE_PAGE(PageIsolated(page), page);
+	SetPageIsolated(page);
 	folio_unlock(folio);
 
 	return true;
@@ -175,8 +194,8 @@ bool isolate_folio_to_list(struct folio *folio, struct list_head *list)
 	if (lru)
 		isolated = folio_isolate_lru(folio);
 	else
-		isolated = isolate_movable_page(&folio->page,
-						ISOLATE_UNEVICTABLE);
+		isolated = isolate_movable_ops_page(&folio->page,
+						    ISOLATE_UNEVICTABLE);
 
 	if (!isolated)
 		return false;
-- 
2.49.0