[PATCH 1/1] mm/thp: clear deferred split shrinker bits when queues drain

[Lance Yang <lance.yang@linux.dev>]

From: Lance Yang <lance.yang@linux.dev>

deferred_split_count() returns the raw list_lru count. When the per-memcg,
per-node list is empty, that count is 0.

That skips scanning, but it does not tell memcg reclaim that the shrinker
is empty. shrink_slab_memcg() only clears the memcg shrinker bit when the
count callback reports SHRINK_EMPTY.

Return SHRINK_EMPTY for an empty deferred split list, so the bit can be
cleared once the queue has drained.

Signed-off-by: Lance Yang <lance.yang@linux.dev>
---
 mm/huge_memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 72f6caf0fec6..62d598290c3b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4397,7 +4397,10 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 static unsigned long deferred_split_count(struct shrinker *shrink,
 		struct shrink_control *sc)
 {
-	return list_lru_shrink_count(&deferred_split_lru, sc);
+	unsigned long count;
+
+	count = list_lru_shrink_count(&deferred_split_lru, sc);
+	return count ?: SHRINK_EMPTY;
 }
 
 static bool thp_underused(struct folio *folio)
-- 
2.49.0