[PATCHv2] mm: migrate LRU_REFS_MASK bits in folio_migrate_flags

["zhaoyang.huang" <zhaoyang.huang@unisoc.com>]

From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>

Bits of LRU_REFS_MASK are not inherited during migration which lead to
new folio start from tier0 when MGLRU enabled. Try to bring as much bits
of folio->flags as possible since compaction and alloc_contig_range
which introduce migration do happen at times.

Suggested-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
---
v2: modification as Yu Zhao suggested
---
---
 include/linux/mm_inline.h | 10 ++++++++++
 mm/migrate.c              |  1 +
 2 files changed, 11 insertions(+)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index f4fe593c1400..6f801c7b36e2 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -291,6 +291,12 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 	return true;
 }
 
+static inline void folio_migrate_refs(struct folio *new, struct folio *old)
+{
+	unsigned long refs = READ_ONCE(old->flags) & LRU_REFS_MASK;
+
+	set_mask_bits(&new->flags, LRU_REFS_MASK, refs);
+}
 #else /* !CONFIG_LRU_GEN */
 
 static inline bool lru_gen_enabled(void)
@@ -313,6 +319,10 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 	return false;
 }
 
+static inline void folio_migrate_refs(struct folio *new, struct folio *old)
+{
+
+}
 #endif /* CONFIG_LRU_GEN */
 
 static __always_inline
diff --git a/mm/migrate.c b/mm/migrate.c
index 923ea80ba744..60c97e235ae7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -618,6 +618,7 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
 	if (folio_test_idle(folio))
 		folio_set_idle(newfolio);
 
+	folio_migrate_refs(newfolio, folio);
 	/*
 	 * Copy NUMA information to the new page, to prevent over-eager
 	 * future migrations of this same page.
-- 
2.25.1