Re: [PATCH v2 2/3] mm/mglru: add tracepoint for scan_folios()

[Baoquan He <baoquan.he@linux.dev>]

On 09/15/26 at 08:17pm, Ridong Chen wrote:
> 
> 
> On 9/15/2026 7:14 PM, Baoquan He wrote:
> > On 09/11/26 at 06:29pm, Ridong Chen wrote:
> > > From: Ridong Chen <chenridong@xiaomi.com>
> > ...snip...
> > > ---
> > >   include/trace/events/vmscan.h | 63 +++++++++++++++++++++++++++++++++++
> > >   mm/vmscan.c                   |  6 ++++
> > >   2 files changed, 69 insertions(+)
> > > 
> > > diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> > > index 8a872990b4be..5defa8f6719c 100644
> > > --- a/include/trace/events/vmscan.h
> > > +++ b/include/trace/events/vmscan.h
> > > @@ -392,6 +392,69 @@ TRACE_EVENT(mm_vmscan_lru_isolate,
> > >   		__print_symbolic(__entry->lru, LRU_NAMES))
> > >   );
> > > +TRACE_EVENT(mm_mglru_scan_folios,
> > > +
> > > +	TP_PROTO(struct lruvec *lruvec,
> > > +		int highest_zoneidx,
> > > +		int order,
> > > +		unsigned long nr_requested,
> > > +		unsigned long nr_scanned,
> > > +		unsigned long nr_sorted,
> > > +		unsigned long nr_skipped,
> > > +		unsigned long nr_taken,
> > > +		int lru,
> > > +		unsigned long max_seq,
> > > +		int tier,
> > > +		unsigned long min_seq),
> > 
> 
> Thank you for your review.
> 
> > Do we need show nid? Guess phone vendor doesn't care about multi-NUMA
> > system.
> > 
> 
> Eh, nid is not an mglru-specific key. Since there are 12 elements here, it
> can't be added here.

Hmm, we print memcg_id but not nid, it may not be so clear. How do you
differentiate several lruvec-s on one memcg? I am not very familiar with
trace mechanism, do we have a element number limit?

Imagine I only want to trace this function, now I can see memcg_id,
zone_idex, while don't know node/lruvec, that's a little pitty. Just my
personal opinion, I could miss anything.

> 
> 
> > And I checked v1 thread, seems Steven suggested to move the two int to
> > avoid extra padding.
> > 
> 
> Yeah, I will update it. I updated v2 to fix Sashiko's issue, before Steven
> had any comment.
> 
> 
> > > +
> > > +	TP_ARGS(lruvec, highest_zoneidx, order, nr_requested, nr_scanned,
> > > +		nr_sorted, nr_skipped, nr_taken, lru, max_seq, tier, min_seq),
> > > +
> > > +	TP_STRUCT__entry(
> > > +		__field(u64, memcg_id)
> > > +		__field(int, highest_zoneidx)
> > > +		__field(int, order)
> > > +		__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(int, lru)
> > > +		__field(unsigned long, max_seq)
> > > +		__field(int, tier)
> > > +		__field(unsigned long, min_seq)
> > > +	),
> > > +
> > > +	TP_fast_assign(
> > > +		__entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec));
> > > +		__entry->highest_zoneidx = highest_zoneidx;
> > > +		__entry->order = order;
> > > +		__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->lru = lru;
> > > +		__entry->max_seq = max_seq;
> > > +		__entry->tier = tier;
> > > +		__entry->min_seq = min_seq;
> > > +	),
> > > +
> > > +	TP_printk("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->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)
> > > +);
> > > +
> > >   TRACE_EVENT(mm_vmscan_write_folio,
> > >   	TP_PROTO(struct folio *folio),
> > > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > > index 2554a6513aa8..67f59aa73fb9 100644
> > > --- a/mm/vmscan.c
> > > +++ b/mm/vmscan.c
> > > @@ -4876,6 +4876,12 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
> > >   	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
> > >   				scanned, skipped, isolated,
> > >   				type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
> > > +	trace_mm_mglru_scan_folios(lruvec,
> > > +				   sc->reclaim_idx, sc->order, nr_to_scan,
> > > +				   scanned, sorted, skipped, isolated,
> > > +				   type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON,
> > > +				   lrugen->max_seq, tier,
> > > +				   lrugen->min_seq[type]);
> > 
> > And seems Steven also suggested to calculate lru, max_seq, min_seq in
> > TP_fast_assign() in v1 which could be missed.
> > 
> 
> Thanks, I will update it following Steven's suggestions.
> 
> 
> >          TP_fast_assign(
> >                  __entry->memcg_id = mem_cgroup_id(lruvec_memcg(lruvec));
> >                  __entry->highest_zoneidx = sc->reclaim_idx;
> >                  __entry->order = sc->order;
> >                  __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->lru = type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON;
> >                  __entry->max_seq = lrugen->max_seq;
> >                  __entry->tier = tier;
> >                  __entry->min_seq = lrugen->min_seq;
> >          ),
> > 
> 
> However, 'sc' is an internal structure, so sc->order cannot be accessed in
> TP_fast_assign(), and I don't think it is worth making scan_control an
> external structure just for this.

Agree.

> 
> > 
> > >   	*isolatedp = isolated;
> > >   	return scanned;
> > > -- 
> > > 2.34.1
> > > 
> 
> -- 
> Best regards
> Ridong
>