[RFC PATCH v4 11/16] mm/mglru: skip gentle reclaim at DEF_PRIORITY for extreme swappiness

For extreme swappiness (<= MIN_SWAPPINESS + 1 or >= MAX_SWAPPINESS),
skip gentle reclaim.
Falling back too easily, even at DEF_PRIORITY, undermines the effect
of extreme swappiness.

This matches the logic in get_type_to_scan(), where we have:
        if (swappiness <= MIN_SWAPPINESS + 1)
                return LRU_GEN_FILE;

        if (swappiness >= MAX_SWAPPINESS)
                return LRU_GEN_ANON;

Signed-off-by: Barry Song (Xiaomi) <[email protected]>
---
 mm/vmscan.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index b6c17ece3b3f..48a068b50678 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -281,6 +281,13 @@ static inline bool is_exec_file_folio(const struct folio *folio,
 	return vma_flags_test(vma_flags, VMA_EXEC_BIT) && folio_is_file_lru(folio);
 }
 
+/* See get_type_to_scan(): these values always select FILE or ANON */
+static inline bool is_extreme_swappiness(int swappiness)
+{
+	return swappiness <= MIN_SWAPPINESS + 1 ||
+	       swappiness >= MAX_SWAPPINESS;
+}
+
 static void set_task_reclaim_state(struct task_struct *task,
 				   struct reclaim_state *rs)
 {
@@ -5094,8 +5101,11 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq,
 	if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS > max_seq)
 		return true;
 
-	/* try to avoid aging, do gentle reclaim at the default priority */
-	if (sc->priority == DEF_PRIORITY)
+	/*
+	 * Try to avoid aging by doing gentle reclaim at the default
+	 * priority. Skip gentle reclaim for extreme swappiness.
+	 */
+	if (sc->priority == DEF_PRIORITY && !is_extreme_swappiness(swappiness))
 		return false;
 
 	/* better to run aging even though eviction is still possible */
-- 
2.34.1