[PATCH v4 0/2] mm/damon: fix the temporal goal tuner's size quota conversion

[Donggeun Yoo <donggeunyoo.kernel@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.

v2: https://lore.kernel.org/damon/20260920023111.2466265-1-donggeunyoo.kernel@gmail.com/
v3: https://lore.kernel.org/damon/20260920122411.610213-1-donggeunyoo.kernel@gmail.com/

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

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

Rebased onto mm-new 8d29b5365d52.

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(-)

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2.53.0