linux-kernel - [PATCH 5/5] mm/damon: hide kdamond and kdamond_lock of damon

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Message-ID: <20260115152047.68415-6-sj@kernel.org>
Date: Thu, 15 Jan 2026 07:20:45 -0800
From: SeongJae Park <sj@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: SeongJae Park <sj@...nel.org>,
	damon@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH 5/5] mm/damon: hide kdamond and kdamond_lock of damon_ctx

There is no DAMON API caller that directly access 'kdamond' and
'kdamond_lock' fields of 'struct damon_ctx'.  Keeping those exposed
could only encourage creative but error-prone usages.  Hide them from
DAMON API callers by marking those as private fields.

Signed-off-by: SeongJae Park <sj@...nel.org>
---
 include/linux/damon.h | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 5b7ea7082134..e6930d8574d3 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -759,23 +759,20 @@ struct damon_attrs {
  * of the monitoring.
  *
  * @attrs:		Monitoring attributes for accuracy/overhead control.
- * @kdamond:		Kernel thread who does the monitoring.
- * @kdamond_lock:	Mutex for the synchronizations with @kdamond.
  *
- * For each monitoring context, one kernel thread for the monitoring is
- * created.  The pointer to the thread is stored in @kdamond.
+ * For each monitoring context, one kernel thread for the monitoring, namely
+ * kdamond, is created.  The pid of kdamond can be retrieved using
+ * damon_kdamond_pid().
  *
- * Once started, the monitoring thread runs until explicitly required to be
- * terminated or every monitoring target is invalid.  The validity of the
- * targets is checked via the &damon_operations.target_valid of @ops.  The
- * termination can also be explicitly requested by calling damon_stop().
- * The thread sets @kdamond to NULL when it terminates. Therefore, users can
- * know whether the monitoring is ongoing or terminated by reading @kdamond.
- * Reads and writes to @kdamond from outside of the monitoring thread must
- * be protected by @kdamond_lock.
+ * Once started, kdamond runs until explicitly required to be terminated or
+ * every monitoring target is invalid.  The validity of the targets is checked
+ * via the &damon_operations.target_valid of @ops.  The termination can also be
+ * explicitly requested by calling damon_stop().  To know if a kdamond is
+ * running, damon_is_running() can be used.
  *
- * Note that the monitoring thread protects only @kdamond via @kdamond_lock.
- * Accesses to other fields must be protected by themselves.
+ * While the kdamond is running, all accesses to &struct damon_ctx from a
+ * thread other than the kdamond should be made using safe DAMON APIs,
+ * including damon_call() and damos_walk().
  *
  * @ops:	Set of monitoring operations for given use cases.
  * @addr_unit:	Scale factor for core to ops address conversion.
@@ -816,10 +813,12 @@ struct damon_ctx {
 	struct damos_walk_control *walk_control;
 	struct mutex walk_control_lock;
 
-/* public: */
+	/* Working thread of the given DAMON context */
 	struct task_struct *kdamond;
+	/* Protects @kdamond field access */
 	struct mutex kdamond_lock;
 
+/* public: */
 	struct damon_operations ops;
 	unsigned long addr_unit;
 	unsigned long min_sz_region;
-- 
2.47.3