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

[Ridong Chen <ridong.chen@linux.dev>]

On 9/11/2026 10:11 PM, Steven Rostedt wrote:
> On Fri, 11 Sep 2026 15:28:47 +0800
> Ridong Chen <ridong.chen@linux.dev> wrote:
> 
>> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
>> index 8a872990b4be..c39dfacef033 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(u64 memcg_id,
>> +		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),
>> +
>> +	TP_ARGS(memcg_id, 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)
> 

Thank you very much for your review.

> Please keep "int"s together. This creates a structure that is used to write
> into the ring buffer. On 64bit machines, the above would add 4 bytes of
> padding after each int, whereas:
> 
> 		__field(unsigned long, max_seq)
> 		__field(unsigned long, min_seq)
> 		__field(int, lru)
> 		__field(int, tier)
> 
> 
> would not.
> 

Will upate.

>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->memcg_id = memcg_id;
>> +		__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..bd1b9ecf2e84 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(mem_cgroup_id(lruvec_memcg(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]);
> 
> Can't this information be processed in the tracepoint? That is:
> 
> 	TP_PROTO(struct lruvec *lruvec,
> 		 struct scan_control *sc,
> 		 struct lru_gen_folio *lrugen,
> 		 unsigned long nr_requested,
> 		 unsigned long nr_scanned,
> 		 unsigned long nr_sorted,
> 		 unsigned long nr_skipped,
> 		 unsigned long nr_taken,
> 		 int type),
> 
> 	TP_ARGS(lruvec, sc, lrugen, nr_requested, nr_scanned,
> 		nr_sorted, nr_skipped, nr_taken, type),
> 
> 	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(unsigned long, max_seq)
> 		__field(unsigned long, min_seq)
> 		__field(int, lru)
> 		__field(int, tier)
> 	),
> 
> 	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;
> 	),
> 
> 
> This moves the code to generate the parameters into the TP_fast_assign()
> which is in a separate text section. It remove code from the work flow
> improving instruction cache.
> 
> Same can be done for that trace_mm_vmscan_lru_isolate() trace event.
> 

Sashiko has reported the same issue, so I updated my series [1] when I received 
Sashiko's report. Thank you again for pointing this out.

[1] https://lore.kernel.org/linux-mm/20260911102939.2485750-3-ridong.chen@linux.dev/

> 
>>   
>>   	*isolatedp = isolated;
>>   	return scanned;
>> -- 

-- 
Best regards
Ridong