[PATCH] mm/damon/core: iterate the regions list from current point in damon_set_regions()

[xiakaixu1987]

From: Kaixu Xia <kaixuxia@xxxxxxxxxxx>

We iterate the whole regions list every time to get the first/last regions
intersecting with the specific range in damon_set_regions(), in order to
add new region or resize existing regions to fit in the specific range.
Actually, it is unnecessary to iterate the new added regions and the
front regions that have been checked. Just iterate the regions list from
the current point using list_for_each_entry_from() every time to improve
performance.
The kunit tests passed:
 [PASSED] damon_test_apply_three_regions1
 [PASSED] damon_test_apply_three_regions2
 [PASSED] damon_test_apply_three_regions3
 [PASSED] damon_test_apply_three_regions4

Signed-off-by: Kaixu Xia <kaixuxia@xxxxxxxxxxx>
---
 include/linux/damon.h | 8 ++++++++
 mm/damon/core.c       | 3 ++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 7b1f4a488230..d54acec048d6 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -463,9 +463,17 @@ static inline struct damon_region *damon_last_region(struct damon_target *t)
 	return list_last_entry(&t->regions_list, struct damon_region, list);
 }
 
+static inline struct damon_region *damon_first_region(struct damon_target *t)
+{
+	return list_first_entry(&t->regions_list, struct damon_region, list);
+}
+
 #define damon_for_each_region(r, t) \
 	list_for_each_entry(r, &t->regions_list, list)
 
+#define damon_for_each_region_from(r, t) \
+	list_for_each_entry_from(r, &t->regions_list, list)
+
 #define damon_for_each_region_safe(r, next, t) \
 	list_for_each_entry_safe(r, next, &t->regions_list, list)
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 7d25dc582fe3..702e1b7e975b 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -195,6 +195,7 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 			damon_destroy_region(r, t);
 	}
 
+	r = damon_first_region(t);
 	/* Add new regions or resize existing regions to fit in the ranges */
 	for (i = 0; i < nr_ranges; i++) {
 		struct damon_region *first = NULL, *last, *newr;
@@ -202,7 +203,7 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 
 		range = &ranges[i];
 		/* Get the first/last regions intersecting with the range */
-		damon_for_each_region(r, t) {
+		damon_for_each_region_from(r, t) {
 			if (damon_intersect(r, range)) {
 				if (!first)
 					first = r;
-- 
2.27.0