[PATCH v6 0/3] cgroup: dmem: add selftest helper and coverage

[Albert Esteve <aesteve@redhat.com>]

Hi all,

This small series adds practical test coverage for the dmem
cgroup controller.

The motivation came from following the recent dmem API discussion in
thread [1]. That discussion considered changing the dmem API and
adding a new knob. Currently there are no dedicated tests covering
dmem behaviour, which makes such changes riskier.

Adding selftests has an additional challenge: dmem charging paths
are driver-driven today, so regression testing is harder unless a
suitable driver is present in the test environment.

This series addresses that by adding:
- an out-of-tree dmem_selftest helper with alloc/free module parameters,
- KB() definition next to existing MB()/GB() helpers
- test_dmem for dmem.max enforcement and byte-accurate dmem.current

The goal is to make dmem behavior easier to validate when evolving the API
and implementation, while keeping tests deterministic and driver-independent.

Thanks.

[1] - https://lore.kernel.org/all/aZoHfloupKvF2oSu@fedora/

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
Changes in v6:
- Drop virtme-ng wrappers
- Build the helper out of tree, drop CONFIG_DMEM_SELFTEST
- Rename charge/uncharge to alloc/free
- Add KB() in cgroup_util.h
- Use cg_read_key_long(), ARRAY_SIZE(), and KB()/MB() size literals
- Drop test_dmem_min/low
- Check dmem.current for exact equality
- stat() the helper once in main() instead of per-subtest
- Link to v5: https://lore.kernel.org/r/20260706-kunit_cgroups-v5-0-6c42c8753468@redhat.com

Changes in v5:
- Change parse_first_region() by find_selftest_region to scan
  dmem.capacity lines
- Use exact equality for limit readback, not values_close()
- Write VM tempfile to $SCRIPT_DIR
- Fix KTAP by dropping outer framing in test_dmem
- Use array for optional vng args to handle paths with spaces
- Respect O=/KBUILD_OUTPUT= when building, per bpf/vmtest.sh convention
- Link to v4: https://lore.kernel.org/r/20260519-kunit_cgroups-v4-0-f6c2f498fae4@redhat.com

Changes in v4:
- Fix charged_pool leak in dmem_selftest_init()
- Replace ssh-based VM approach in vmtest-dmem.sh with vng --exec
- Add main() wrapper to vmtest-dmem.sh
- Other small fixes suggested by Sashiko
- Link to v3: https://lore.kernel.org/r/20260504-kunit_cgroups-v3-0-4eac90b76f91@redhat.com

Changes in v3:
- Set charged flag on unexpected over-limit charge success.
- Add CONFIG_DMEM_SELFTEST=m to selftest config.
- Simplify -v to a boolean; single -v was a no-op.
- Unquote kernel_opt to avoid empty-string arg to vng.
- Document -b in usage() output.
- Link to v2: https://lore.kernel.org/r/20260421-kunit_cgroups-v2-0-bb6675d8249c@redhat.com

Changes in v2:
- Fix debugfs_create_dir() error check
- Fix module teardown race: call dmem_selftest_remove() before
  uncharging so debugfs files are torn down
- Use IS_ERR_OR_NULL() in selftest() sanity check
- Add CONFIG_CGROUP_DMEM=y to the cgroup selftest config
- Replace config-file parsing in check_guest_requirements() with
  a direct check of /sys/fs/cgroup/cgroup.controllers
- Add new patch 4 (from Eric Chanudet): vmtest-dmem.sh -b flag
  to configure and build a local kernel tree
- Link to v1: https://lore.kernel.org/r/20260327-kunit_cgroups-v1-0-971b3c739a00@redhat.com

---
Albert Esteve (3):
      selftests: cgroup: Add dmem_selftest helper module
      selftests: cgroup: Add KB() helper
      selftests: cgroup: Add dmem selftest coverage

 tools/testing/selftests/cgroup/.gitignore          |   1 +
 tools/testing/selftests/cgroup/Makefile            |   3 +
 tools/testing/selftests/cgroup/config              |   1 +
 .../selftests/cgroup/lib/include/cgroup_util.h     |   1 +
 tools/testing/selftests/cgroup/test_dmem.c         | 314 +++++++++++++++++++++
 .../testing/selftests/cgroup/test_modules/Makefile |  17 ++
 .../selftests/cgroup/test_modules/dmem_selftest.c  | 146 ++++++++++
 7 files changed, 483 insertions(+)
---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20260318-kunit_cgroups-7fb0b9e64017

Best regards,
-- 
Albert Esteve <aesteve@redhat.com>