Claude review: cgroup/dmem: allow double-charging dmem allocations to memcg

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Overall Series Review

Subject: cgroup/dmem: allow double-charging dmem allocations to memcg
Author: Eric Chanudet <echanude@redhat.com>
Patches: 8
Reviewed: 2026-05-25T22:42:50.439377

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This is a v2 2-patch series by Eric Chanudet that adds optional "double-charging" of dmem (device memory) cgroup allocations to the memory controller (memcg). The motivation is to let administrators account device memory allocations against both the dmem controller and the standard memory controller simultaneously.

**Architecture:** Patch 1 adds `mem_cgroup_dmem_charge()`/`mem_cgroup_dmem_uncharge()` helpers in mm/memcontrol.c. Patch 2 wires them into kernel/cgroup/dmem.c with a root-only `dmem.memcg` control file and a 4-state lock machine.

**Overall assessment:** The design is reasonable — the lock-on-first-charge approach prevents mid-life accounting inconsistencies, and keeping the control at root-only is appropriate. However, there are several correctness issues around charging/uncharging symmetry, the stat output units, error-path behavior in the write handler, and a potential silent failure mode in the charge path that need attention.

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