Re: [RFC PATCH v2 18/28] mm/damon: trace probe_hits

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 12 May 2026 07:36:33 -0700
SeongJae Park <sj@kernel.org> wrote:

> Introduce a new tracepoint for exposing the per-region per-probe
> positive sample count via tracefs.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  include/trace/events/damon.h | 36 ++++++++++++++++++++++++++++++++++++
>  mm/damon/core.c              |  7 +++++++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
> index 7e25f4469b81b..d7b94c7640217 100644
> --- a/include/trace/events/damon.h
> +++ b/include/trace/events/damon.h
> @@ -130,6 +130,42 @@ TRACE_EVENT(damon_monitor_intervals_tune,
>  	TP_printk("sample_us=%lu", __entry->sample_us)
>  );
>  
> +TRACE_EVENT(damon_aggregated_v2,
> +
> +	TP_PROTO(unsigned int target_id, struct damon_region *r,
> +		unsigned int nr_regions, unsigned int nr_probes),
> +
> +	TP_ARGS(target_id, r, nr_regions, nr_probes),
> +
> +	TP_STRUCT__entry(
> +		__field(unsigned long, target_id)
> +		__field(unsigned long, start)
> +		__field(unsigned long, end)
> +		__field(unsigned int, nr_regions)
> +		__field(unsigned int, nr_accesses)
> +		__field(unsigned int, age)
> +		__dynamic_array(unsigned char, probe_hits, nr_probes)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->target_id = target_id;
> +		__entry->start = r->ar.start;
> +		__entry->end = r->ar.end;
> +		__entry->nr_regions = nr_regions;
> +		__entry->nr_accesses = r->nr_accesses;
> +		__entry->age = r->age;
> +		memcpy(__get_dynamic_array(probe_hits), r->probe_hits,
> +			sizeof(*r->probe_hits) * nr_probes);
> +	),
> +
> +	TP_printk("target_id=%lu nr_regions=%u %lu-%lu: %u %u probe_hits=%s",
> +			__entry->target_id, __entry->nr_regions,
> +			__entry->start, __entry->end,
> +			__entry->nr_accesses, __entry->age,
> +			__print_hex(__get_dynamic_array(probe_hits),
> +				__get_dynamic_array_len(probe_hits)))
> +);
> +
>  TRACE_EVENT(damon_aggregated,
>  
>  	TP_PROTO(unsigned int target_id, struct damon_region *r,
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index fe6c789f2cecb..14b15c9876516 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -1905,6 +1905,11 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
>  {
>  	struct damon_target *t;
>  	unsigned int ti = 0;	/* target's index */
> +	unsigned int nr_probes = 0;
> +	struct damon_probe *probe;
> +
> +	damon_for_each_probe(probe, c)
> +		nr_probes++;

Is the above logic needed when the tracepoint isn't enabled? If not, then you could add:

	if (trace_damon_aggregated_v2_enabled()) {
		damon_for_each_probe(probe, c)
			nr_probes++;
	}

And change the tracepoint to be a conditional tracepoint:

TRACE_EVENT_CONDITION(damon_aggregated_v2,

	TP_PROTO(..),

	TP_ARGS(..),

	TP_CONDITION(nr_probes > 0),

	[..]

And then the tracepoint is only triggered if nr_probes is greater than zero
(to handle races between the tracepoint being enabled in between the above
check and where it triggers).

-- Steve

>  
>  	damon_for_each_target(t, c) {
>  		struct damon_region *r;
> @@ -1913,6 +1918,8 @@ static void kdamond_reset_aggregated(struct damon_ctx *c)
>  			int i;
>  
>  			trace_damon_aggregated(ti, r, damon_nr_regions(t));
> +			trace_damon_aggregated_v2(ti, r, damon_nr_regions(t),
> +					nr_probes);
>  			damon_warn_fix_nr_accesses_corruption(r);
>  			r->last_nr_accesses = r->nr_accesses;
>  			r->nr_accesses = 0;