Claude review: cgroup/dmem: implement dmem.high soft limit via prioritized eviction

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Overall Series Review

Subject: cgroup/dmem: implement dmem.high soft limit via prioritized eviction
Author: Qiliang Yuan <realwujing@gmail.com>
Patches: 1
Reviewed: 2026-06-04T15:52:23.141901

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This is a single-patch series (v4) adding a `dmem.high` soft limit to the dmem cgroup v2 controller. The concept is sound: when eviction is triggered (e.g., by a `max` limit hit), BOs from cgroups exceeding their `dmem.high` soft limit are evicted first, providing a prioritized reclaim mechanism rather than the rejected sleep-on-allocation approach from v1.

The cgroupfs plumbing (control file, get/set, initialization) follows existing patterns well. However, the TTM eviction changes have two significant bugs: Pass 2 runs with blocking lock instead of trylock (the `trylock_only` flag is never restored after Pass 1), and the `try_high` path in `dmem_cgroup_state_evict_valuable()` skips the hierarchy check between `limit_pool` and `test_pool`, meaning BOs from completely unrelated cgroups can be evicted if any of their ancestors happens to exceed its high limit.

**Verdict: Needs revision** — the trylock regression and the missing hierarchy check need to be fixed before this can be merged.

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