[PATCH 0/2] cgroup/dmem: add per-region event counters

[Hongfu Li]

This patch series adds event counters to the device memory (dmem) cgroup
controller.

The dmem controller exposes per-region limits and current usage, but
not how often those limits are hit.  It is hard to tell whether failures
come from this cgroup, a parent limit, or pressure elsewhere in the
hierarchy.

To provide that visibility, this series introduces:
  - dmem.events:       reports hierarchical low/max counts per region.
  - dmem.events.local: reports per-region low/max counts for this cgroup only.

Patch overview:

Patch 1/2:
  - Add dmem.events with hierarchical low/max counters per region.
  - Record dmem.max allocation failures and dmem.low protection events.
  - Document the interface in cgroup-v2.rst.

Patch 2/2:
  - Add dmem.events.local for local-only per-region counts.
  - Share the events show logic between both files.
  - Update cgroup-v2.rst accordingly.

Example output (dmem.events):

  drm/0000:03:00.0/vram0 low 0 max 3
  drm/0000:03:00.0/stolen low 0 max 0

  low  - reclaim/eviction considered the cgroup below its effective
         dmem.low protection
  max  - allocation failed because the cgroup or an ancestor hit dmem.max

Both files exist for all non-root cgroups, like dmem.max and dmem.current.

These patches have been tested locally.

Hongfu Li (2):
  cgroup/dmem: add per-region event counters
  cgroup/dmem: introduce dmem.events.local for local counts

 Documentation/admin-guide/cgroup-v2.rst | 17 +++++
 kernel/cgroup/dmem.c                    | 85 ++++++++++++++++++++++++-
 2 files changed, 101 insertions(+), 1 deletion(-)

-- 
2.25.1