mm/damon/core: implement damos_walk()

Introduce a new core layer interface, damos_walk().  It aims to replace
some damon_callback usages that access DAMOS schemes applied regions of
ongoing kdamond with additional synchronizations.  It receives a function
pointer and asks kdamond to invoke it for any region that it tried to
apply any DAMOS action within one scheme apply interval for every scheme
of it.  The function further waits until the kdamond finishes the
invocations for every scheme, or cancels the request, and returns.

The kdamond invokes the function as requested within the main loop.  If it
is deactivated by DAMOS watermarks or going out of the main loop, it marks
the request as canceled, so that damos_walk() can wakeup and return.

Link: https://lkml.kernel.org/r/20250103174400.54890-8-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, 31 insertions, 2 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index ac2d42a50751..2889de3526c3 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -352,6 +352,31 @@ struct damos_filter {
 	struct list_head list;
 };
 
+struct damon_ctx;
+struct damos;
+
+/**
+ * struct damos_walk_control - Control damos_walk().
+ *
+ * @walk_fn:	Function to be called back for each region.
+ * @data:	Data that will be passed to walk functions.
+ *
+ * Control damos_walk(), which requests specific kdamond to invoke the given
+ * function to each region that eligible to apply actions of the kdamond's
+ * schemes.  Refer to damos_walk() for more details.
+ */
+struct damos_walk_control {
+	void (*walk_fn)(void *data, struct damon_ctx *ctx,
+			struct damon_target *t, struct damon_region *r,
+			struct damos *s);
+	void *data;
+/* private: internal use only */
+	/* informs if the kdamond finished handling of the walk request */
+	struct completion completion;
+	/* informs if the walk is canceled. */
+	bool canceled;
+};
+
 /**
  * struct damos_access_pattern - Target access pattern of the given scheme.
  * @min_sz_region:	Minimum size of target regions.
@@ -415,6 +440,8 @@ struct damos {
 	 * @action
 	 */
 	unsigned long next_apply_sis;
+	/* informs if ongoing DAMOS walk for this scheme is finished */
+	bool walk_completed;
 /* public: */
 	struct damos_quota quota;
 	struct damos_watermarks wmarks;
@@ -442,8 +469,6 @@ enum damon_ops_id {
 	NR_DAMON_OPS,
 };
 
-struct damon_ctx;
-
 /**
  * struct damon_operations - Monitoring operations for given use cases.
  *
@@ -656,6 +681,9 @@ struct damon_ctx {
 	struct damon_call_control *call_control;
 	struct mutex call_control_lock;
 
+	struct damos_walk_control *walk_control;
+	struct mutex walk_control_lock;
+
 /* public: */
 	struct task_struct *kdamond;
 	struct mutex kdamond_lock;
@@ -804,6 +832,7 @@ 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 damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
 
 int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 				unsigned long *start, unsigned long *end);