Claude review: cgroup/dmem: introduce a peak file

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: cgroup/dmem: introduce a peak file
Author: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Patches: 1
Reviewed: 2026-05-16T10:32:53.178730

---

This is a single-patch series (v3) that adds a read-only `dmem.peak` file to the dmem cgroup controller, mirroring the existing `memory.peak` concept. The implementation is clean and minimal — it reuses the existing `page_counter` watermark infrastructure and the `dmemcg_limit_show` callback pattern already established for `dmem.current`.

The patch is **correct and safe to merge** with minor nits. The watermark is already maintained hierarchically by `page_counter_try_charge()` / `page_counter_charge()`, so no additional charge-path changes are needed. The `READ_ONCE` usage is appropriate and matches how the memory controller reads the watermark.

**Issues worth noting:**

1. **Incomplete changelog**: The v3 changelog still contains `EDITME` placeholders — this should be fixed before merge, though it's metadata only.
2. **No selftest coverage**: There's no selftest for this new file, and no existing dmem selftest infrastructure was found. A basic test would strengthen the patch.
3. **Read-only vs. read-write**: The commit message says "for now, make it read-only." The memory controller's `memory.peak` is read-write (writing resets the peak per-FD). This is fine as stated — reset support can come later — but the documentation should probably mention this difference more explicitly or note that reset support is planned.

---

---
Generated by Claude Code Patch Reviewer