Claude review: cgroup/dmem: introduce a peak file

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Overall Series Review

Subject: cgroup/dmem: introduce a peak file
Author: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Patches: 6
Reviewed: 2026-05-07T13:37:55.340313

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This 2-patch series adds a `dmem.peak` cgroup file, mirroring the existing `memory.peak` functionality for the DRM device-memory cgroup controller. Patch 1 extracts the peak-reset logic from memcontrol into a shared helper; Patch 2 uses it to implement per-region peak tracking in dmem.

**The overall approach is sound and the core logic is correct.** The reference counting is carefully handled, concurrent read/write races are safe due to appropriate use of `READ_ONCE`/`WRITE_ONCE` and fallback to global watermark, and the per-fd peak semantics correctly mirror the existing memory.peak behavior.

There are a few design concerns worth discussing, mainly around the addition of a dmem-specific `pool` pointer into the generic `cgroup_of_peak` struct, and the unused `seq_file *` parameter added to four getter functions. Neither is a correctness issue, but both are layering concerns that reviewers from the cgroup/mm side may push back on.

No bugs found. The series is in good shape for a v1.

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