linux-kernel - [RFC PATCH 01/12] mm/damon/core: introduce nr

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Message-ID: <20251123184329.85287-2-sj@kernel.org>
Date: Sun, 23 Nov 2025 10:43:15 -0800
From: SeongJae Park <sj@...nel.org>
To: 
Cc: SeongJae Park <sj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	damon@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH 01/12] mm/damon/core: introduce nr_snapshots damos stat

DAMON generates monitoring results snapshots for every sampling
interval.  DAMOS applies given schemes on the regions of the snapshots,
for every apply interval of the scheme.

DAMOS stat informs a given scheme has tried to how many memory entities
and applied, in the region and byte level.  In some use cases including
user-space oriented tuning and investigations, it is useful to know that
in the DAMON-snapshot level.  Introduce a new stat, namely nr_snapshots
for DAMON core API callers.

Signed-off-by: SeongJae Park <sj@...nel.org>
---
 include/linux/damon.h |  3 +++
 mm/damon/core.c       | 13 ++++++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 3813373a9200..1d8a1515e75a 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -330,6 +330,8 @@ struct damos_watermarks {
  * @sz_ops_filter_passed:
  *		Total bytes that passed ops layer-handled DAMOS filters.
  * @qt_exceeds: Total number of times the quota of the scheme has exceeded.
+ * @nr_snapshots:
+ *		Total number of DAMON snapshots that the scheme has tried.
  *
  * "Tried an action to a region" in this context means the DAMOS core logic
  * determined the region as eligible to apply the action.  The access pattern
@@ -355,6 +357,7 @@ struct damos_stat {
 	unsigned long sz_applied;
 	unsigned long sz_ops_filter_passed;
 	unsigned long qt_exceeds;
+	unsigned long nr_snapshots;
 };
 
 /**
diff --git a/mm/damon/core.c b/mm/damon/core.c
index f9fc0375890a..af922d5e500c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -157,6 +157,12 @@ void damon_destroy_region(struct damon_region *r, struct damon_target *t)
 	damon_free_region(r);
 }
 
+static bool damon_is_last_region(struct damon_region *r,
+		struct damon_target *t)
+{
+	return list_is_last(&t->regions_list, &r->list);
+}
+
 /*
  * Check whether a region is intersecting an address range
  *
@@ -1949,10 +1955,11 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		if (damos_skip_charged_region(t, &r, s, c->min_sz_region))
 			continue;
 
-		if (!damos_valid_target(c, t, r, s))
-			continue;
+		if (damos_valid_target(c, t, r, s))
+			damos_apply_scheme(c, t, r, s);
 
-		damos_apply_scheme(c, t, r, s);
+		if (damon_is_last_region(r, t))
+			s->stat.nr_snapshots++;
 	}
 }
 
-- 
2.47.3