[RFC PATCH 06/18] mm/damon/core: add a DAMON callback for scheme target regions check

[SeongJae Park <sj@kernel.org>]

For deep level investigation of DAMON, knowing exactly to what regions
each DAMON-based operation scheme is applied is helpful.  It can also be
very helpful for efficient monitoring results passing when the user has
interest in regions of specific access patterns.  Add a new DAMON
callback that will be called before each scheme is applied to each
region, to provide the functionality to the kernel API users.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 5 +++++
 mm/damon/core.c       | 6 +++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 620ada094c3b..35630634d790 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -357,6 +357,7 @@ struct damon_operations {
  * @after_wmarks_check:	Called after each schemes' watermarks check.
  * @after_sampling:	Called after each sampling.
  * @after_aggregation:	Called after each aggregation.
+ * @before_damos_apply:	Called before applying DAMOS action.
  * @before_terminate:	Called before terminating the monitoring.
  * @private:		User private data.
  *
@@ -385,6 +386,10 @@ struct damon_callback {
 	int (*after_wmarks_check)(struct damon_ctx *context);
 	int (*after_sampling)(struct damon_ctx *context);
 	int (*after_aggregation)(struct damon_ctx *context);
+	int (*before_damos_apply)(struct damon_ctx *context,
+			struct damon_target *target,
+			struct damon_region *region,
+			struct damos *scheme);
 	void (*before_terminate)(struct damon_ctx *context);
 };
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 9ee9f752f6fc..f196feed78c7 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -765,6 +765,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 	unsigned long sz = damon_sz_region(r);
 	struct timespec64 begin, end;
 	unsigned long sz_applied = 0;
+	int err = 0;
 
 	if (c->ops.apply_scheme) {
 		if (quota->esz && quota->charged_sz + sz > quota->esz) {
@@ -775,7 +776,10 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 			damon_split_region_at(t, r, sz);
 		}
 		ktime_get_coarse_ts64(&begin);
-		sz_applied = c->ops.apply_scheme(c, t, r, s);
+		if (c->callback.before_damos_apply)
+			err = c->callback.before_damos_apply(c, t, r, s);
+		if (!err)
+			sz_applied = c->ops.apply_scheme(c, t, r, s);
 		ktime_get_coarse_ts64(&end);
 		quota->total_charged_ns += timespec64_to_ns(&end) -
 			timespec64_to_ns(&begin);
-- 
2.25.1