Re: [PATCH v5 5/6] mm/mglru: add tracepoint for scan_folios()

[Baoquan He]

On 10/31/26 at 05:00pm, Ridong Chen wrote:
> From: Ridong Chen <chenridong@xxxxxxxxxx>
> 
> MGLRU's scan_folios() emits the classic-LRU tracepoint
> trace_mm_vmscan_lru_isolate(), which predates MGLRU. It reports the
> scan/isolate counts and the LRU type, but carries no generation or
> memcg context, so a trace of an MGLRU run cannot tell which memcg a
> given scan belongs to, nor how far reclaim has progressed through the
> generations.
> 
> Add mm_mglru_scan_folios next to it, reporting the same counters plus
> nr_sorted (folios moved to a younger generation by sort_folio()) and
> the context the classic tracepoint lacks: the node id and memcg id of
> the lruvec, and the max_seq, tier and min_seq of the type being
> scanned.
> 
> Now that struct scan_control is visible to the trace header, pass sc,
> lruvec, type and tier straight in and derive everything else in
> TP_fast_assign(), so nothing is computed at the call site when the
> event is disabled. The int fields are grouped at the end of the entry
> to avoid padding on 64-bit.
> 
> scan_folios() is the MGLRU-specific layer where folios are actually
> scanned, so it has no classic-LRU counterpart. The existing tracepoint
> is left unchanged.
> 
> Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
> ---
>  mm/trace_vmscan.h | 66 +++++++++++++++++++++++++++++++++++++++++++++++
>  mm/vmscan.c       |  2 ++
>  2 files changed, 68 insertions(+)
> 
> diff --git a/mm/trace_vmscan.h b/mm/trace_vmscan.h
> index b2ad83e5f25e..8148b8224422 100644
> --- a/mm/trace_vmscan.h
> +++ b/mm/trace_vmscan.h
> @@ -392,6 +392,72 @@ TRACE_EVENT(mm_vmscan_lru_isolate,
>  		__print_symbolic(__entry->lru, LRU_NAMES))
>  );
>  
> +#ifdef CONFIG_LRU_GEN
> +TRACE_EVENT(mm_mglru_scan_folios,
> +
> +	TP_PROTO(struct lruvec *lruvec,
> +		 struct scan_control *sc,
> +		 unsigned long nr_requested,
> +		 unsigned long nr_scanned,
> +		 unsigned long nr_sorted,
> +		 unsigned long nr_skipped,
> +		 unsigned long nr_taken,
> +		 int type,
> +		 int tier),
> +
> +	TP_ARGS(lruvec, sc, nr_requested, nr_scanned, nr_sorted, nr_skipped,
> +		nr_taken, type, tier),
> +
> +	TP_STRUCT__entry(
> +		__field(u64, memcg_id)
> +		__field(unsigned long, nr_requested)
> +		__field(unsigned long, nr_scanned)
> +		__field(unsigned long, nr_sorted)
> +		__field(unsigned long, nr_skipped)
> +		__field(unsigned long, nr_taken)
> +		__field(unsigned long, max_seq)
> +		__field(unsigned long, min_seq)
> +		__field(int, nid)

Now it has nid printed out, it's cool. 

This patch looks good to me, thanks.

Reviewed-by: Baoquan He <baoquan.he@xxxxxxxxx>


> +		__field(int, highest_zoneidx)
> +		__field(int, order)
> +		__field(int, lru)
> +		__field(int, tier)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec));
> +		__entry->nr_requested = nr_requested;
> +		__entry->nr_scanned = nr_scanned;
> +		__entry->nr_sorted = nr_sorted;
> +		__entry->nr_skipped = nr_skipped;
> +		__entry->nr_taken = nr_taken;
> +		__entry->max_seq = lruvec->lrugen.max_seq;
> +		__entry->min_seq = lruvec->lrugen.min_seq[type];
> +		__entry->nid = lruvec_pgdat(lruvec)->node_id;
> +		__entry->highest_zoneidx = sc->reclaim_idx;
> +		__entry->order = sc->order;
> +		__entry->lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> +		__entry->tier = tier;
> +	),
> +
> +	TP_printk("nid=%d memcg_id=%llu classzone=%d order=%d nr_requested=%lu nr_scanned=%lu nr_sorted=%lu nr_skipped=%lu nr_taken=%lu lru=%s max_seq=%lu tier=%d min_seq=%lu",
> +		__entry->nid,
> +		__entry->memcg_id,
> +		__entry->highest_zoneidx,
> +		__entry->order,
> +		__entry->nr_requested,
> +		__entry->nr_scanned,
> +		__entry->nr_sorted,
> +		__entry->nr_skipped,
> +		__entry->nr_taken,
> +		__print_symbolic(__entry->lru, LRU_NAMES),
> +		__entry->max_seq,
> +		__entry->tier,
> +		__entry->min_seq)
> +);
> +
> +#endif /* CONFIG_LRU_GEN */
> +
>  TRACE_EVENT(mm_vmscan_write_folio,
>  
>  	TP_PROTO(struct folio *folio),
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 15e9184a580a..ff51fee872f8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4852,6 +4852,8 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
>  	trace_mm_vmscan_lru_isolate(sc, nr_to_scan,
>  				    scanned, skipped, isolated,
>  				    type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
> +	trace_mm_mglru_scan_folios(lruvec, sc, nr_to_scan, scanned, sorted,
> +				   skipped, isolated, type, tier);
>  
>  	*isolatedp = isolated;
>  	return scanned;
> -- 
> 2.43.0
>