mm/mglru: use a smaller batch for reclaim

With a fixed number to reclaim calculated at the beginning, making each
following step smaller should reduce the lock contention and avoid
over-aggressive reclaim of folios, as it will abort earlier when the
number of folios to be reclaimed is reached.

Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Chen Ridong <chenridong@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Kairui Song <kasong@tencent.com>

Author: ryncsn

mm/vmscan.c

@@ -4880,7 +4880,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 			break;
 		}
 
-		nr_batch = min(nr_to_scan, MAX_LRU_BATCH);
+		nr_batch = min(nr_to_scan, MIN_LRU_BATCH);
 		delta = evict_folios(nr_batch, lruvec, sc, swappiness);
 		if (!delta)
 			break;