mm/damon/core: introduce damon_call()

Introduce a new DAMON core API function, damon_call().  It aims to replace
some damon_callback usages that access damon_ctx of ongoing kdamond with
additional synchronizations.  It receives a function pointer, let the
parallel kdamond invokes the function, and returns after the invocation is
finished, or canceled due to some races.

kdamond invokes the function inside the main loop after sampling is done. 
If it is deactivated by DAMOS watermarks or already out of the main loop,
mark the request as canceled so that damon_call() can wakeup and return.

Link: https://lkml.kernel.org/r/20250103174400.54890-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index a67f2c4940e9..ac2d42a50751 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -552,6 +552,27 @@ struct damon_callback {
 	void (*before_terminate)(struct damon_ctx *context);
 };
 
+/*
+ * struct damon_call_control - Control damon_call().
+ *
+ * @fn:			Function to be called back.
+ * @data:		Data that will be passed to @fn.
+ * @return_code:	Return code from @fn invocation.
+ *
+ * Control damon_call(), which requests specific kdamond to invoke a given
+ * function.  Refer to damon_call() for more details.
+ */
+struct damon_call_control {
+	int (*fn)(void *data);
+	void *data;
+	int return_code;
+/* private: internal use only */
+	/* informs if the kdamond finished handling of the request */
+	struct completion completion;
+	/* informs if the kdamond canceled @fn infocation */
+	bool canceled;
+};
+
 /**
  * struct damon_attrs - Monitoring attributes for accuracy/overhead control.
  *
@@ -632,6 +653,9 @@ struct damon_ctx {
 	/* for scheme quotas prioritization */
 	unsigned long *regions_score_histogram;
 
+	struct damon_call_control *call_control;
+	struct mutex call_control_lock;
+
 /* public: */
 	struct task_struct *kdamond;
 	struct mutex kdamond_lock;
@@ -779,6 +803,8 @@ static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs
 int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive);
 int damon_stop(struct damon_ctx **ctxs, int nr_ctxs);
 
+int damon_call(struct damon_ctx *ctx, struct damon_call_control *control);
+
 int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end);