mm/damon: fix the temporal goal tuner's size quota conversion

From: Donggeun Yoo <[email protected]>

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/[email protected]
- 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/[email protected]/
v2: https://lore.kernel.org/damon/[email protected]/

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