[RFC PATCH v5 13/14] mm/mglru: Make swappiness=1 file reclaim more aggressive

["Barry Song (Xiaomi)" <baohua@kernel.org>]

In MGLRU, swappiness=200 favors anon reclaim, while swappiness=1
favors file reclaim. Swappiness=0 allows only file reclaim, while
swappiness=201 allows only anon reclaim. Thus, swappiness=1 and
swappiness=200 are counterparts for file and anon reclaim,
respectively.

Before this patchset, get_type_to_scan() always returned
LRU_GEN_ANON for swappiness=200 and LRU_GEN_FILE for swappiness=1.

For swappiness=200, file_factor is set to 0 at higher reclaim
priorities. Similarly, anon_factor is set to 0 for swappiness=1
at higher reclaim priorities, making the two settings behave
similarly, although the thresholds are slightly different.

This allows file pages to be reclaimed more aggressively and
benefits workloads that prioritize file reclaim by using
swappiness=1.

Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/vmscan.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 81e81d69e67e..6d5a823667e0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -5113,7 +5113,11 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
 	anon_weight = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE] / size_bias;
 	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
 
-	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
+	if (swappiness == MIN_SWAPPINESS + 1)
+		anon_factor = sc->priority <= DEF_PRIORITY / 2 ?
+			      refault_rate[LRU_GEN_FILE] * anon_weight : 0;
+	else
+		anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
 	if (swappiness == MAX_SWAPPINESS)
 		file_factor = sc->priority < DEF_PRIORITY / 2 ?
 			      refault_rate[LRU_GEN_ANON] * file_weight : 0;
-- 
2.34.1