linux-kernel - [PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan

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Message-Id: <20251204122355.1822919-1-chenridong@huaweicloud.com>
Date: Thu,  4 Dec 2025 12:23:55 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: akpm@...ux-foundation.org,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	hannes@...xchg.org,
	david@...nel.org,
	mhocko@...nel.org,
	zhengqi.arch@...edance.com,
	shakeel.butt@...ux.dev,
	lorenzo.stoakes@...cle.com,
	yuzhao@...gle.com,
	jaewon31.kim@...sung.com,
	ioworker0@...il.com
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...wei.com
Subject: [PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan_folios

From: Chen Ridong <chenridong@...wei.com>

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.

Fixes: 8c2214fc9a47 ("mm: multi-gen LRU: reuse some legacy trace events")
Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 mm/vmscan.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 584f41eb4c14..a0a74cac947b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4404,7 +4404,8 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	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);
 
@@ -4464,7 +4465,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *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)
-- 
2.34.1