[PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan_folios

[PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan_folios

[Chen Ridong]

From: Chen Ridong <chenridong@huawei.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@huawei.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

Re: [PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan_folios

[David Hildenbrand (Red Hat)]

On 12/4/25 13:23, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.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@huawei.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)

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David

Re: [PATCH -next v2] mm: vmscan: correct nr_requested tracing in scan_folios

[Lance Yang]

On 2025/12/4 20:23, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.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@huawei.com>
> ---

LGTM, feel free to add:

Reviewed-by: Lance Yang <lance.yang@linux.dev>