[PATCH RESEND v2 0/2] mm/damon: add a tracepoint for damos apply target regions

[PATCH RESEND v2 0/2] mm/damon: add a tracepoint for damos apply target regions

[SeongJae Park]

Changlog
--------

From original v2 post
(https://lore.kernel.org/damon/20230912183559.4733-1-sj@kernel.org/)
- Fix header
- Rebase on latest mm-unstable

From v1
(https://lore.kernel.org/damon/20230911045908.97649-1-sj@kernel.org/)
- Get scheme/target indices only when the trace is enabled (Steven Rostedt)

From RFC
(https://lore.kernel.org/damon/20230827004045.49516-1-sj@kernel.org/)
- Fix the 4 byte hole (Steven Rostedt)
- Add documentation

Description
-----------

DAMON provides damon_aggregated tracepoint to let users record full monitoring
results.  Sometimes, users need to record monitoring results of specific
pattern.  DAMOS tried regions directory of DAMON sysfs interface allows it, but
the interface is mainly designed for snapshots and therefore would be
inefficient for such recording.  Implement yet another tracepoint for efficient
support of the usecase.


SeongJae Park (2):
  mm/damon/core: add a tracepoint for damos apply target regions
  Docs/admin-guide/mm/damon/usage: document damos_before_apply
    tracepoint

 Documentation/admin-guide/mm/damon/usage.rst | 37 +++++++++++++++----
 include/trace/events/damon.h                 | 39 ++++++++++++++++++++
 mm/damon/core.c                              | 32 +++++++++++++++-
 3 files changed, 100 insertions(+), 8 deletions(-)


base-commit: 8abeac23845e94681a163299a52d802b82475761
-- 
2.25.1

[PATCH RESEND v2 1/2] mm/damon/core: add a tracepoint for damos apply target regions

[SeongJae Park]

DAMON provides damon_aggregated tracepoint, which exposes details of
each region and its access monitoring results.  It is useful for
getting whole monitoring results, e.g., for recording purposes.

For investigations of DAMOS, DAMON Sysfs interface provides DAMOS
statistics and tried_regions directory.  But, those provides only
statistics and snapshots.  If the scheme is frequently applied and if
the user needs to know every detail of DAMOS behavior, the
snapshot-based interface could be insufficient and expensive.

As a last resort, userspace users need to record the all monitoring
results via damon_aggregated tracepoint and simulate how DAMOS would
worked.  It is unnecessarily complicated.  DAMON kernel API users,
meanwhile, can do that easily via before_damos_apply() callback field of
'struct damon_callback', though.

Add a tracepoint that will be called just after before_damos_apply()
callback for more convenient investigations of DAMOS.  The tracepoint
exposes all details about each regions, similar to damon_aggregated
tracepoint.

Please note that DAMOS is currently not only for memory management but
also for query-like efficient monitoring results retrievals (when 'stat'
action is used).  Until now, only statistics or snapshots were
supported.  Addition of this tracepoint allows efficient full recording
of DAMOS-based filtered monitoring results.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/trace/events/damon.h | 39 ++++++++++++++++++++++++++++++++++++
 mm/damon/core.c              | 32 ++++++++++++++++++++++++++++-
 2 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 0b8d13bde17a..19930bb7af9a 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h
@@ -9,6 +9,45 @@
 #include <linux/types.h>
 #include <linux/tracepoint.h>
 
+TRACE_EVENT_CONDITION(damos_before_apply,
+
+	TP_PROTO(unsigned int context_idx, unsigned int scheme_idx,
+		unsigned int target_idx, struct damon_region *r,
+		unsigned int nr_regions, bool do_trace),
+
+	TP_ARGS(context_idx, target_idx, scheme_idx, r, nr_regions, do_trace),
+
+	TP_CONDITION(do_trace),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, context_idx)
+		__field(unsigned int, scheme_idx)
+		__field(unsigned long, target_idx)
+		__field(unsigned long, start)
+		__field(unsigned long, end)
+		__field(unsigned int, nr_accesses)
+		__field(unsigned int, age)
+		__field(unsigned int, nr_regions)
+	),
+
+	TP_fast_assign(
+		__entry->context_idx = context_idx;
+		__entry->scheme_idx = scheme_idx;
+		__entry->target_idx = target_idx;
+		__entry->start = r->ar.start;
+		__entry->end = r->ar.end;
+		__entry->nr_accesses = r->nr_accesses;
+		__entry->age = r->age;
+		__entry->nr_regions = nr_regions;
+	),
+
+	TP_printk("ctx_idx=%u scheme_idx=%u target_idx=%lu nr_regions=%u %lu-%lu: %u %u",
+			__entry->context_idx, __entry->scheme_idx,
+			__entry->target_idx, __entry->nr_regions,
+			__entry->start, __entry->end,
+			__entry->nr_accesses, __entry->age)
+);
+
 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 ca631dd88b33..3ca34a252a3c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -950,6 +950,33 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 	struct timespec64 begin, end;
 	unsigned long sz_applied = 0;
 	int err = 0;
+	/*
+	 * We plan to support multiple context per kdamond, as DAMON sysfs
+	 * implies with 'nr_contexts' file.  Nevertheless, only single context
+	 * per kdamond is supported for now.  So, we can simply use '0' context
+	 * index here.
+	 */
+	unsigned int cidx = 0;
+	struct damos *siter;		/* schemes iterator */
+	unsigned int sidx = 0;
+	struct damon_target *titer;	/* targets iterator */
+	unsigned int tidx = 0;
+	bool do_trace = false;
+
+	/* get indices for trace_damos_before_apply() */
+	if (trace_damos_before_apply_enabled()) {
+		damon_for_each_scheme(siter, c) {
+			if (siter == s)
+				break;
+			sidx++;
+		}
+		damon_for_each_target(titer, c) {
+			if (titer == t)
+				break;
+			tidx++;
+		}
+		do_trace = true;
+	}
 
 	if (c->ops.apply_scheme) {
 		if (quota->esz && quota->charged_sz + sz > quota->esz) {
@@ -964,8 +991,11 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 		ktime_get_coarse_ts64(&begin);
 		if (c->callback.before_damos_apply)
 			err = c->callback.before_damos_apply(c, t, r, s);
-		if (!err)
+		if (!err) {
+			trace_damos_before_apply(cidx, sidx, tidx, r,
+					damon_nr_regions(t), do_trace);
 			sz_applied = c->ops.apply_scheme(c, t, r, s);
+		}
 		ktime_get_coarse_ts64(&end);
 		quota->total_charged_ns += timespec64_to_ns(&end) -
 			timespec64_to_ns(&begin);
-- 
2.25.1

Re: [PATCH RESEND v2 1/2] mm/damon/core: add a tracepoint for damos apply target regions

[Steven Rostedt]

On Wed, 13 Sep 2023 02:20:49 +0000
SeongJae Park <sj@kernel.org> wrote:

> DAMON provides damon_aggregated tracepoint, which exposes details of
> each region and its access monitoring results.  It is useful for
> getting whole monitoring results, e.g., for recording purposes.
> 
> For investigations of DAMOS, DAMON Sysfs interface provides DAMOS
> statistics and tried_regions directory.  But, those provides only
> statistics and snapshots.  If the scheme is frequently applied and if
> the user needs to know every detail of DAMOS behavior, the
> snapshot-based interface could be insufficient and expensive.
> 
> As a last resort, userspace users need to record the all monitoring
> results via damon_aggregated tracepoint and simulate how DAMOS would
> worked.  It is unnecessarily complicated.  DAMON kernel API users,
> meanwhile, can do that easily via before_damos_apply() callback field of
> 'struct damon_callback', though.
> 
> Add a tracepoint that will be called just after before_damos_apply()
> callback for more convenient investigations of DAMOS.  The tracepoint
> exposes all details about each regions, similar to damon_aggregated
> tracepoint.
> 
> Please note that DAMOS is currently not only for memory management but
> also for query-like efficient monitoring results retrievals (when 'stat'
> action is used).  Until now, only statistics or snapshots were
> supported.  Addition of this tracepoint allows efficient full recording
> of DAMOS-based filtered monitoring results.
> 

From a tracing point of view.

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve