[PATCH 1/8] mm/damon/core: add a callback for scheme target regions check

[SeongJae Park <sj@kernel.org>]

Getting DAMON monitoring results of only specific access pattern (e.g.,
getting address ranges of memory that not accessed at all for two
minutes) can be useful for efficient monitoring of the system.  The
information can also be helpful for deep level investigation of
DAMON-based operation schemes.

For that, users need to record (in case of the user space users) or
iterate (in case of the kernel space users) full monitoring results and
filter it out for the specific access pattern.  In case of the DAMOS
investigation, users will even need to simulate DAMOS' quota and
prioritization mechanisms.  It's inefficient and complex.

Add a new DAMON callback that will be called before each scheme is
applied to each region.  DAMON kernel API users will be able to do the
query-like monitoring results collection, or DAMOS investigation in an
efficient and simple way using it.

Commits for providing the capability to the user space users will
follow.

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 80d5937fe337..ceec75b88ef9 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -772,6 +772,7 @@ 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) {
@@ -782,7 +783,10 @@ 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