[PATCH v2 2/2] mm/damon/vaddr: Add 'nr_piece == 1' check in damon_va_evenly_split_region()

[Zheng Yejian <zhengyejian@huaweicloud.com>]

As discussed in [1], damon_va_evenly_split_region() is called to
size-evenly split a region into 'nr_pieces' small regions,
when nr_pieces == 1, no actual split is required. Check that case
for better code readability and add a simple kunit testcase.

[1] https://lore.kernel.org/all/20241021163316.12443-1-sj@kernel.org/

Signed-off-by: Zheng Yejian <zhengyejian@huaweicloud.com>
---
 mm/damon/tests/vaddr-kunit.h | 1 +
 mm/damon/vaddr.c             | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
index a149e354bb26..b9a03e4e29e5 100644
--- a/mm/damon/tests/vaddr-kunit.h
+++ b/mm/damon/tests/vaddr-kunit.h
@@ -300,6 +300,7 @@ static void damon_test_split_evenly(struct kunit *test)
 	damon_test_split_evenly_fail(test, 0, 100, 0);
 	damon_test_split_evenly_succ(test, 0, 100, 10);
 	damon_test_split_evenly_succ(test, 5, 59, 5);
+	damon_test_split_evenly_succ(test, 4, 6, 1);
 	damon_test_split_evenly_succ(test, 0, 3, 2);
 	damon_test_split_evenly_fail(test, 5, 6, 2);
 }
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index dba3b2f4d758..25db0a582c27 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -72,6 +72,9 @@ static int damon_va_evenly_split_region(struct damon_target *t,
 	if (!r || !nr_pieces)
 		return -EINVAL;
 
+	if (nr_pieces == 1)
+		return 0;
+
 	orig_end = r->ar.end;
 	sz_orig = damon_sz_region(r);
 	sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
-- 
2.25.1