[PATCH v5 0/2] mm/damon: fix the temporal goal tuner's size quota conversion

[SJ Park]

From: Donggeun Yoo <donggeuny...@gmail.com>

damos_goal_tune_esz_bp_temporal() hands the size quota to
damos_set_effective_quota() through quota->esz_bp in basis points, and
the multiply that gets it there is unchecked. On 32-bit it wraps above
429496 bytes, and a wrapped product below 10000 divides to a zero
effective quota. damos_quota_is_full() is then true on the first test
of every charge window, so the scheme makes no progress for as long as
the goal is unachieved.

Patch 1 bounds the conversion. Patch 2 pins the boundary in the core
kunit suite, where the new test would fail without patch 1 on any word
size.

Changes in v5
- v4: https://lore.kernel.org/20260923002600.182544...@gmail.com
- Collec R-b: from SJ for patch 1.
- Rebase to the latest mm-new.
Changes in v4, from SJ Park's review of v2; the code is unchanged:
- patch 1: drop the 256 MiB mention
- patch 1: say what the user sees before saying the setup is unlikely
- patch 1: cut the closing paragraph to "Bound the multiply."
- patch 2: unchanged, and carries the Reviewed-by
v3: https://lore.kernel.org/damon/20260920122411.610213...@gmail.com/
v2: https://lore.kernel.org/damon/20260920023111.246626...@gmail.com/

v3 was posted before the discussion on v2 had finished. My mistake;
this version was held until the thread settled.

DAMON kunit on x86_64: 39 tests, all passing with both patches; 38
passing and damos_test_esz_goal_temporal failing with patch 2 alone.

Donggeun Yoo (2):
mm/damon/core: prevent size quota overflow in the temporal goal tuner
mm/damon/tests/core-kunit: test the temporal tuner's size quota
conversion

mm/damon/core.c | 2 +-
mm/damon/tests/core-kunit.h | 48 +++++++++++++++++++++++++++++++++++++
2 files changed, 49 insertions(+), 1 deletion(-)


base-commit: 2fbc36fcb37d79b22b904066065952050a7ea307
--
2.47.3

[SJ Park]

From: Donggeun Yoo <donggeuny...@gmail.com>

damos_goal_tune_esz_bp_temporal() encodes the size quota in basis
points, so the conversion is exact only up to ULONG_MAX / 10000. Pin
the three sizes around that boundary: the largest one that fits, the
first one that does not, and ULONG_MAX.

Signed-off-by: Donggeun Yoo <donggeuny...@gmail.com>
Reviewed-by: SJ Park <s...@kernel.org>
Signed-off-by: SJ Park <s...@kernel.org>
---
mm/damon/tests/core-kunit.h | 48 +++++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index ef4b8b85d67b..caf582882f5f 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -2284,6 +2284,53 @@ static void damon_test_rand(struct kunit *test)
}
}

+static void damos_test_esz_goal_temporal(struct kunit *test)
+{
+ struct damos_access_pattern pattern = {};
+ struct damos_watermarks wmarks = {};
+ struct damos_quota quota = {
+ .goal_tuner = DAMOS_QUOTA_GOAL_TUNER_TEMPORAL,
+ };
+ struct damos_quota_goal *goal;
+ struct damon_ctx *ctx;
+ struct damos *s;
+
+ ctx = damon_new_ctx();
+ KUNIT_ASSERT_NOT_NULL(test, ctx);
+
+ s = damon_new_scheme(&pattern, DAMOS_STAT, 0, &quota, &wmarks,
+ NUMA_NO_NODE);
+ if (!s) {
+ damon_destroy_ctx(ctx);
+ kunit_skip(test, "scheme alloc fail");
+ }
+ damon_add_scheme(ctx, s);
+
+ goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, 10000);
+ if (!goal) {
+ damon_destroy_ctx(ctx);
+ kunit_skip(test, "quota goal alloc fail");
+ }
+ goal->current_value = 0;
+ damos_add_quota_goal(&s->quota, goal);
+
+ /* The largest size quota the basis-point conversion can hold. */
+ s->quota.sz = ULONG_MAX / 10000;
+ damos_set_effective_quota(ctx, s);
+ KUNIT_EXPECT_EQ(test, s->quota.esz, ULONG_MAX / 10000);
+
+ /* Any larger one saturates instead of wrapping. */
+ s->quota.sz = ULONG_MAX / 10000 + 1;
+ damos_set_effective_quota(ctx, s);
+ KUNIT_EXPECT_EQ(test, s->quota.esz, ULONG_MAX / 10000);
+
+ s->quota.sz = ULONG_MAX;
+ damos_set_effective_quota(ctx, s);
+ KUNIT_EXPECT_EQ(test, s->quota.esz, ULONG_MAX / 10000);
+
+ damon_destroy_ctx(ctx);
+}
+
static struct kunit_case damon_test_cases[] = {
KUNIT_CASE(damon_test_target),
KUNIT_CASE(damon_test_regions),
@@ -2324,6 +2371,7 @@ static struct kunit_case damon_test_cases[] = {
KUNIT_CASE(damon_test_is_last_region),
KUNIT_CASE(damon_test_walk_control_obsolete),
KUNIT_CASE(damon_test_rand),
+ KUNIT_CASE(damos_test_esz_goal_temporal),
{},
};

--
2.47.3