Re: [PATCH 2/2] mm/damon: add trace event for effective size quota

Hi Steven,

On Wed, 9 Jul 2025 12:21:23 -0400 Steven Rostedt [off-list ref] wrote:

On Fri,  4 Jul 2025 15:14:08 -0700
SeongJae Park [off-list ref] wrote:

quoted

Aim-oriented DAMOS quota auto-tuning is an important and recommended
feature for DAMOS users.  Add a trace event for the observability of the
tuned quota and tuning itself.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/trace/events/damon.h | 26 ++++++++++++++++++++++++++
 mm/damon/core.c              | 20 +++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 32c611076023..36b2cdf47dce 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h

@@ -9,6 +9,32 @@
 #include <linux/types.h>
 #include <linux/tracepoint.h>
 
+TRACE_EVENT_CONDITION(damos_esz,
+
+	TP_PROTO(unsigned int context_idx, unsigned int scheme_idx,
+		unsigned long esz, bool do_trace),
+
+	TP_ARGS(context_idx, scheme_idx, esz, do_trace),
+
+	TP_CONDITION(do_trace),

Please explain to me why you are using a conditional here?

There is no reason to make this conditional.  Maybe I was out of my mind.

[...]

quoted

--- a/mm/damon/core.c
+++ b/mm/damon/core.c

@@ -2011,12 +2011,26 @@ static void damos_set_effective_quota(struct damos_quota *quota)
 	quota->esz = esz;
 }
 
+static void damos_trace_esz(struct damon_ctx *c, struct damos *s,
+		struct damos_quota *quota)
+{
+	unsigned int cidx = 0, sidx;
+	struct damos *siter;
+
+	damon_for_each_scheme(siter, c) {
+		if (siter == s)
+			break;
+		sidx++;
+	}
+	trace_damos_esz(cidx, sidx, quota->esz, true);

It's set to true, so it's not even a conditional anymore. The compiler
will likely optimize it out!

You're right.

Andrew, could you please add below fixup patch?


Thanks,
SJ

=================== >8 ======================
From 13975534cad603410837c5eca299f0a24ad802a1 Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Wed, 9 Jul 2025 11:22:39 -0700
Subject: [PATCH] mm/damon: make damos_esz unconditional trace event

It has no reason to be conditional.  Make it unconditional trace event.

Fixes: 9a365a71b830 ("mm/damon: add trace event for effective size quota") # mm-unstable
Closes: https://lore.kernel.org/20250709122123.779c874f@batman.local.home (local)
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/trace/events/damon.h | 8 +++-----
 mm/damon/core.c              | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 2e4d7d281fa7..fc2c61ccc887 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h

@@ -9,14 +9,12 @@
 #include <linux/types.h>
 #include <linux/tracepoint.h>
 
-TRACE_EVENT_CONDITION(damos_esz,
+TRACE_EVENT(damos_esz,
 
 	TP_PROTO(unsigned int context_idx, unsigned int scheme_idx,
-		unsigned long esz, bool do_trace),
+		unsigned long esz),
 
-	TP_ARGS(context_idx, scheme_idx, esz, do_trace),
-
-	TP_CONDITION(do_trace),
+	TP_ARGS(context_idx, scheme_idx, esz),
 
 	TP_STRUCT__entry(
 		__field(unsigned int, context_idx)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 0f7d8b37c91d..775e097b6538 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c

@@ -2223,7 +2223,7 @@ static void damos_trace_esz(struct damon_ctx *c, struct damos *s,
 			break;
 		sidx++;
 	}
-	trace_damos_esz(cidx, sidx, quota->esz, true);
+	trace_damos_esz(cidx, sidx, quota->esz);
 }
 
 static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)

-- 
2.39.5