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

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

Link: https://lkml.kernel.org/r/1662477527-13003-1-git-send-email-kaixuxia@tencent.comSigned-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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)
 

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;