[PATCH v2 2/5] mm: migrate: add folio_isolate_movable()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

Like isolate_lru_page(), make isolate_movable_page() as a wrapper
around folio_isolate_movable(), since isolate_movable_page() always
fails on a tail page, return immediately for a tail page in the
warpper, and the wrapper will be removed once all callers are
converted to folio_isolate_movable().

Note all isolate_movable_page() users increased page reference, so
replace redundant folio_get_nontail_page() with folio_get() and add
a reference count check into folio_isolate_movable().

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 include/linux/migrate.h |  4 +++
 mm/migrate.c            | 54 +++++++++++++++++++++++------------------
 2 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 002e49b2ebd9..0a33f751596c 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -70,6 +70,7 @@ int migrate_pages(struct list_head *l, new_folio_t new, free_folio_t free,
 		  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 folio_isolate_movable(struct folio *folio, 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,
@@ -92,6 +93,9 @@ static inline struct folio *alloc_migration_target(struct folio *src,
 	{ return NULL; }
 static inline bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	{ return false; }
+static inline bool folio_isolate_movable(struct folio *folio,
+					 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/migrate.c b/mm/migrate.c
index 6f9c62c746be..704102cc3951 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -58,31 +58,30 @@
 
 #include "internal.h"
 
-bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+/**
+ * folio_isolate_movable() - Try to isolate a non-lru movable folio.
+ * @folio: Folio to isolate.
+ *
+ * Must be called with an elevated refcount on the folio.
+ *
+ * Return: true if the folio was isolated, false otherwise
+ */
+bool folio_isolate_movable(struct folio *folio, isolate_mode_t mode)
 {
-	struct folio *folio = folio_get_nontail_page(page);
 	const struct movable_operations *mops;
 
-	/*
-	 * Avoid burning cycles with pages that are yet under __free_pages(),
-	 * or just got freed under us.
-	 *
-	 * In case we 'win' a race for a movable page being freed under us and
-	 * raise its refcount preventing __free_pages() from doing its job
-	 * the put_page() at the end of this block will take care of
-	 * release this page, thus avoiding a nasty leakage.
-	 */
-	if (!folio)
-		goto out;
+	VM_BUG_ON_FOLIO(!folio_ref_count(folio), folio);
+
+	folio_get(folio);
 
 	if (unlikely(folio_test_slab(folio)))
 		goto out_putfolio;
 	/* Pairs with smp_wmb() in slab freeing, e.g. SLUB's __free_slab() */
 	smp_rmb();
 	/*
-	 * Check movable flag before taking the page lock because
-	 * we use non-atomic bitops on newly allocated page flags so
-	 * unconditionally grabbing the lock ruins page's owner side.
+	 * Check movable flag before taking the folio lock because
+	 * we use non-atomic bitops on newly allocated folio flags so
+	 * unconditionally grabbing the lock ruins folio's owner side.
 	 */
 	if (unlikely(!__folio_test_movable(folio)))
 		goto out_putfolio;
@@ -92,15 +91,15 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 		goto out_putfolio;
 
 	/*
-	 * As movable pages are not isolated from LRU lists, concurrent
-	 * compaction threads can race against page migration functions
-	 * as well as race against the releasing a page.
+	 * As movable folios are not isolated from LRU lists, concurrent
+	 * compaction threads can race against folio migration functions
+	 * as well as race against the releasing a folio.
 	 *
-	 * In order to avoid having an already isolated movable page
+	 * In order to avoid having an already isolated movable folio
 	 * being (wrongly) re-isolated while it is under migration,
-	 * or to avoid attempting to isolate pages being released,
-	 * lets be sure we have the page lock
-	 * before proceeding with the movable page isolation steps.
+	 * or to avoid attempting to isolate folios being released,
+	 * lets be sure we have the folio lock
+	 * before proceeding with the movable folio isolation steps.
 	 */
 	if (unlikely(!folio_trylock(folio)))
 		goto out_putfolio;
@@ -125,10 +124,17 @@ bool isolate_movable_page(struct page *page, isolate_mode_t mode)
 	folio_unlock(folio);
 out_putfolio:
 	folio_put(folio);
-out:
 	return false;
 }
 
+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+	if (PageTail(page))
+		return false;
+
+	return folio_isolate_movable((struct folio *)page, mode);
+}
+
 static void putback_movable_folio(struct folio *folio)
 {
 	const struct movable_operations *mops = folio_movable_ops(folio);
-- 
2.27.0