mm/damon/core: preserve quota state when constructing schemes

From: Karl Mehltretter <[email protected]>

damon_commit_ctx() first commits the running context's parameters to a temporary context for validating proposed updates. Constructing the temporary schemes clears the running schemes' quota state because damon_new_scheme() initializes the quota passed as a parameter before copying it to the new scheme. Even an update later rejected with -EINVAL loses the running quota state.

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

Note: below are test results and changelogs that could be removed from the final commit log.

In the v1 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.

KUnit was rerun after the rebase on x86-64 and i386. With only patch 2 applied, the two new tests fail. With the fix, all 46 DAMON KUnit tests pass on both architectures.

The v1 DAMON selftests showed no new failures (QEMU TCG guest; the wss_estimation test missed its accuracy bounds with and without the fix).

Changes from v2
- v2: https://lore.kernel.org/[email protected]
- Collect R-b: from SJ for patch 1.
- Rebase to latest mm-new.
- Add a note for starting point of test results and changelogs.
- Fix typos in patch 1: s/detault/default/ s/occationally/occasionally/.
- Update series subject prefix.
Changes from v1
- v1: https://lore.kernel.org/r/[email protected]/
- Collect SJ's Reviewed-by for patch 2.
- Explain the running-context validation in the opening paragraph.
- Clarify which quota is passed as a parameter and use "commit" for the context operation.
- Point Fixes to commit 60bd24f272d0 ("mm/damon/sysfs: test commit input against realistic destination"). Drop the redundant stable version comment.
- Rebase onto mm-new. No changes to the fix or test logic.

Karl Mehltretter (2):
mm/damon/core: preserve the quota passed to damon_new_scheme() mm/damon/tests/core-kunit: test preservation of quota state

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

base-commit: 0fa0454423ab5bbe40db5783aab8ae29b40adf89

2.47.3