mm: vmscan: correct nr_requested tracing in scan_folios

When enabling vmscan tracing, it is observed that nr_requested is always
4096, which is confusing.

mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...
mm_vmscan_lru_isolate: classzone=3 order=0 nr_requested=4096 ...

This is because it prints MAX_LRU_BATCH, which is meaningless as it's a
constant. To fix this, modify it to print capped valued.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 8c2214fc9a47 ("mm: multi-gen LRU: reuse some legacy trace events")
Signed-off-by: Chen Ridong <[e-mail]>
Acked-by: David Hildenbrand (Red Hat) <[e-mail]>
Reviewed-by: Lance Yang <[e-mail]>
Cc: Axel Rasmussen <[e-mail]>
Cc: Jaewon Kim <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Cc: Lu Jialin <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Qi Zheng <[e-mail]>
Cc: Shakeel Butt <[e-mail]>
Cc: Wei Xu <[e-mail]>
Cc: Yuanchu Xie <[e-mail]>
Cc: Yu Zhao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/vmscan.c

···
 	int scanned = 0;
 	int isolated = 0;
 	int skipped = 0;
-	int remaining = min(nr_to_scan, MAX_LRU_BATCH);
+	int scan_batch = min(nr_to_scan, MAX_LRU_BATCH);
+	int remaining = scan_batch;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
 
···
 	count_memcg_events(memcg, item, isolated);
 	count_memcg_events(memcg, PGREFILL, sorted);
 	__count_vm_events(PGSCAN_ANON + type, isolated);
-	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, MAX_LRU_BATCH,
+	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, scan_batch,
 				scanned, skipped, isolated,
 				type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
 	if (type == LRU_GEN_FILE)