damon_new_scheme() initializes the caller's quota in place before copying
it. When damon_commit_ctx() clones the running context for validation,
the quota pointer belongs to a running scheme. Constructing the temporary
scheme therefore clears the running scheme's quota state, even if the
proposed update is later rejected with -EINVAL.

Initialize the new scheme's copy instead, and add KUnit tests for the
constructor and for accepted and rejected context updates.

In a live test with damo, a scheme with a plain 64 KiB size quota and a
60-second reset interval uses its quota, and a full "damo tune" with
unchanged parameters then lets it try another 64 KiB within the same
window. With the fix, sz_tried stays at 64 KiB.

With only patch 2 applied, the two new tests fail on x86-64 and i386.
With the fix, all 43 DAMON KUnit tests pass on both, and the DAMON
selftests show no new failures (QEMU TCG guest; the wss_estimation test
misses its accuracy bounds with and without the fix).

Karl Mehltretter (2):
  mm/damon/core: preserve the caller's quota in damon_new_scheme()
  mm/damon/tests/core-kunit: test preservation of caller quota state

 mm/damon/core.c             |   6 +-
 mm/damon/tests/core-kunit.h | 107 ++++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+), 3 deletions(-)


base-commit: 185111f116aabf202d12ce440c0f6e9bae073514
-- 
2.53.0